Add sources for API 35
Downloaded from https://dl.google.com/android/repository/source-35_r01.zip
using SdkManager in Studio
Test: None
Change-Id: I83f78aa820b66edfdc9f8594d17bc7b6cacccec1
diff --git a/android-35/java/lang/invoke/MethodHandles.java b/android-35/java/lang/invoke/MethodHandles.java
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+/*
+ * Copyright (c) 2008, 2017, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation. Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package java.lang.invoke;
+
+import sun.invoke.util.VerifyAccess;
+import sun.invoke.util.Wrapper;
+import sun.reflect.Reflection;
+
+import java.lang.reflect.*;
+import java.nio.ByteOrder;
+import java.util.List;
+import java.util.Arrays;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+import java.util.Objects;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import static java.lang.invoke.MethodHandleStatics.*;
+import static java.lang.invoke.MethodHandleStatics.newIllegalArgumentException;
+import static java.lang.invoke.MethodType.methodType;
+
+/**
+ * This class consists exclusively of static methods that operate on or return
+ * method handles. They fall into several categories:
+ * <ul>
+ * <li>Lookup methods which help create method handles for methods and fields.
+ * <li>Combinator methods, which combine or transform pre-existing method handles into new ones.
+ * <li>Other factory methods to create method handles that emulate other common JVM operations or control flow patterns.
+ * </ul>
+ * <p>
+ * @author John Rose, JSR 292 EG
+ * @since 1.7
+ */
+public class MethodHandles {
+
+ private MethodHandles() { } // do not instantiate
+
+ // Android-changed: We do not use MemberName / MethodHandleImpl.
+ //
+ // private static final MemberName.Factory IMPL_NAMES = MemberName.getFactory();
+ // static { MethodHandleImpl.initStatics(); }
+ // See IMPL_LOOKUP below.
+
+ //// Method handle creation from ordinary methods.
+
+ /**
+ * Returns a {@link Lookup lookup object} with
+ * full capabilities to emulate all supported bytecode behaviors of the caller.
+ * These capabilities include <a href="MethodHandles.Lookup.html#privacc">private access</a> to the caller.
+ * Factory methods on the lookup object can create
+ * <a href="MethodHandleInfo.html#directmh">direct method handles</a>
+ * for any member that the caller has access to via bytecodes,
+ * including protected and private fields and methods.
+ * This lookup object is a <em>capability</em> which may be delegated to trusted agents.
+ * Do not store it in place where untrusted code can access it.
+ * <p>
+ * This method is caller sensitive, which means that it may return different
+ * values to different callers.
+ * <p>
+ * For any given caller class {@code C}, the lookup object returned by this call
+ * has equivalent capabilities to any lookup object
+ * supplied by the JVM to the bootstrap method of an
+ * <a href="package-summary.html#indyinsn">invokedynamic instruction</a>
+ * executing in the same caller class {@code C}.
+ * @return a lookup object for the caller of this method, with private access
+ */
+ // Android-changed: Remove caller sensitive.
+ // @CallerSensitive
+ public static Lookup lookup() {
+ return new Lookup(Reflection.getCallerClass());
+ }
+
+ /**
+ * Returns a {@link Lookup lookup object} which is trusted minimally.
+ * It can only be used to create method handles to
+ * publicly accessible fields and methods.
+ * <p>
+ * As a matter of pure convention, the {@linkplain Lookup#lookupClass lookup class}
+ * of this lookup object will be {@link java.lang.Object}.
+ *
+ * <p style="font-size:smaller;">
+ * <em>Discussion:</em>
+ * The lookup class can be changed to any other class {@code C} using an expression of the form
+ * {@link Lookup#in publicLookup().in(C.class)}.
+ * Since all classes have equal access to public names,
+ * such a change would confer no new access rights.
+ * A public lookup object is always subject to
+ * <a href="MethodHandles.Lookup.html#secmgr">security manager checks</a>.
+ * Also, it cannot access
+ * <a href="MethodHandles.Lookup.html#callsens">caller sensitive methods</a>.
+ * @return a lookup object which is trusted minimally
+ */
+ public static Lookup publicLookup() {
+ return Lookup.PUBLIC_LOOKUP;
+ }
+
+ // Android-removed: Documentation related to the security manager and module checks
+ /**
+ * Returns a {@link Lookup lookup object} with full capabilities to emulate all
+ * supported bytecode behaviors, including <a href="MethodHandles.Lookup.html#privacc">
+ * private access</a>, on a target class.
+ * @param targetClass the target class
+ * @param lookup the caller lookup object
+ * @return a lookup object for the target class, with private access
+ * @throws IllegalArgumentException if {@code targetClass} is a primitive type or array class
+ * @throws NullPointerException if {@code targetClass} or {@code caller} is {@code null}
+ * @throws IllegalAccessException is not thrown on Android
+ * @since 9
+ */
+ public static Lookup privateLookupIn(Class<?> targetClass, Lookup lookup) throws IllegalAccessException {
+ // Android-removed: SecurityManager calls
+ // SecurityManager sm = System.getSecurityManager();
+ // if (sm != null) sm.checkPermission(ACCESS_PERMISSION);
+ if (targetClass.isPrimitive())
+ throw new IllegalArgumentException(targetClass + " is a primitive class");
+ if (targetClass.isArray())
+ throw new IllegalArgumentException(targetClass + " is an array class");
+ // BEGIN Android-removed: There is no module information on Android
+ /**
+ * Module targetModule = targetClass.getModule();
+ * Module callerModule = lookup.lookupClass().getModule();
+ * if (!callerModule.canRead(targetModule))
+ * throw new IllegalAccessException(callerModule + " does not read " + targetModule);
+ * if (targetModule.isNamed()) {
+ * String pn = targetClass.getPackageName();
+ * assert pn.length() > 0 : "unnamed package cannot be in named module";
+ * if (!targetModule.isOpen(pn, callerModule))
+ * throw new IllegalAccessException(targetModule + " does not open " + pn + " to " + callerModule);
+ * }
+ * if ((lookup.lookupModes() & Lookup.MODULE) == 0)
+ * throw new IllegalAccessException("lookup does not have MODULE lookup mode");
+ * if (!callerModule.isNamed() && targetModule.isNamed()) {
+ * IllegalAccessLogger logger = IllegalAccessLogger.illegalAccessLogger();
+ * if (logger != null) {
+ * logger.logIfOpenedForIllegalAccess(lookup, targetClass);
+ * }
+ * }
+ */
+ // END Android-removed: There is no module information on Android
+ return new Lookup(targetClass);
+ }
+
+
+ /**
+ * Performs an unchecked "crack" of a
+ * <a href="MethodHandleInfo.html#directmh">direct method handle</a>.
+ * The result is as if the user had obtained a lookup object capable enough
+ * to crack the target method handle, called
+ * {@link java.lang.invoke.MethodHandles.Lookup#revealDirect Lookup.revealDirect}
+ * on the target to obtain its symbolic reference, and then called
+ * {@link java.lang.invoke.MethodHandleInfo#reflectAs MethodHandleInfo.reflectAs}
+ * to resolve the symbolic reference to a member.
+ * <p>
+ * If there is a security manager, its {@code checkPermission} method
+ * is called with a {@code ReflectPermission("suppressAccessChecks")} permission.
+ * @param <T> the desired type of the result, either {@link Member} or a subtype
+ * @param target a direct method handle to crack into symbolic reference components
+ * @param expected a class object representing the desired result type {@code T}
+ * @return a reference to the method, constructor, or field object
+ * @exception SecurityException if the caller is not privileged to call {@code setAccessible}
+ * @exception NullPointerException if either argument is {@code null}
+ * @exception IllegalArgumentException if the target is not a direct method handle
+ * @exception ClassCastException if the member is not of the expected type
+ * @since 1.8
+ */
+ public static <T extends Member> T
+ reflectAs(Class<T> expected, MethodHandle target) {
+ MethodHandleImpl directTarget = getMethodHandleImpl(target);
+ // Given that this is specified to be an "unchecked" crack, we can directly allocate
+ // a member from the underlying ArtField / Method and bypass all associated access checks.
+ return expected.cast(directTarget.getMemberInternal());
+ }
+
+ /**
+ * A <em>lookup object</em> is a factory for creating method handles,
+ * when the creation requires access checking.
+ * Method handles do not perform
+ * access checks when they are called, but rather when they are created.
+ * Therefore, method handle access
+ * restrictions must be enforced when a method handle is created.
+ * The caller class against which those restrictions are enforced
+ * is known as the {@linkplain #lookupClass lookup class}.
+ * <p>
+ * A lookup class which needs to create method handles will call
+ * {@link #lookup MethodHandles.lookup} to create a factory for itself.
+ * When the {@code Lookup} factory object is created, the identity of the lookup class is
+ * determined, and securely stored in the {@code Lookup} object.
+ * The lookup class (or its delegates) may then use factory methods
+ * on the {@code Lookup} object to create method handles for access-checked members.
+ * This includes all methods, constructors, and fields which are allowed to the lookup class,
+ * even private ones.
+ *
+ * <h1><a name="lookups"></a>Lookup Factory Methods</h1>
+ * The factory methods on a {@code Lookup} object correspond to all major
+ * use cases for methods, constructors, and fields.
+ * Each method handle created by a factory method is the functional
+ * equivalent of a particular <em>bytecode behavior</em>.
+ * (Bytecode behaviors are described in section 5.4.3.5 of the Java Virtual Machine Specification.)
+ * Here is a summary of the correspondence between these factory methods and
+ * the behavior the resulting method handles:
+ * <table border=1 cellpadding=5 summary="lookup method behaviors">
+ * <tr>
+ * <th><a name="equiv"></a>lookup expression</th>
+ * <th>member</th>
+ * <th>bytecode behavior</th>
+ * </tr>
+ * <tr>
+ * <td>{@link java.lang.invoke.MethodHandles.Lookup#findGetter lookup.findGetter(C.class,"f",FT.class)}</td>
+ * <td>{@code FT f;}</td><td>{@code (T) this.f;}</td>
+ * </tr>
+ * <tr>
+ * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticGetter lookup.findStaticGetter(C.class,"f",FT.class)}</td>
+ * <td>{@code static}<br>{@code FT f;}</td><td>{@code (T) C.f;}</td>
+ * </tr>
+ * <tr>
+ * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSetter lookup.findSetter(C.class,"f",FT.class)}</td>
+ * <td>{@code FT f;}</td><td>{@code this.f = x;}</td>
+ * </tr>
+ * <tr>
+ * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStaticSetter lookup.findStaticSetter(C.class,"f",FT.class)}</td>
+ * <td>{@code static}<br>{@code FT f;}</td><td>{@code C.f = arg;}</td>
+ * </tr>
+ * <tr>
+ * <td>{@link java.lang.invoke.MethodHandles.Lookup#findVirtual lookup.findVirtual(C.class,"m",MT)}</td>
+ * <td>{@code T m(A*);}</td><td>{@code (T) this.m(arg*);}</td>
+ * </tr>
+ * <tr>
+ * <td>{@link java.lang.invoke.MethodHandles.Lookup#findStatic lookup.findStatic(C.class,"m",MT)}</td>
+ * <td>{@code static}<br>{@code T m(A*);}</td><td>{@code (T) C.m(arg*);}</td>
+ * </tr>
+ * <tr>
+ * <td>{@link java.lang.invoke.MethodHandles.Lookup#findSpecial lookup.findSpecial(C.class,"m",MT,this.class)}</td>
+ * <td>{@code T m(A*);}</td><td>{@code (T) super.m(arg*);}</td>
+ * </tr>
+ * <tr>
+ * <td>{@link java.lang.invoke.MethodHandles.Lookup#findConstructor lookup.findConstructor(C.class,MT)}</td>
+ * <td>{@code C(A*);}</td><td>{@code new C(arg*);}</td>
+ * </tr>
+ * <tr>
+ * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectGetter lookup.unreflectGetter(aField)}</td>
+ * <td>({@code static})?<br>{@code FT f;}</td><td>{@code (FT) aField.get(thisOrNull);}</td>
+ * </tr>
+ * <tr>
+ * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectSetter lookup.unreflectSetter(aField)}</td>
+ * <td>({@code static})?<br>{@code FT f;}</td><td>{@code aField.set(thisOrNull, arg);}</td>
+ * </tr>
+ * <tr>
+ * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
+ * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
+ * </tr>
+ * <tr>
+ * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflectConstructor lookup.unreflectConstructor(aConstructor)}</td>
+ * <td>{@code C(A*);}</td><td>{@code (C) aConstructor.newInstance(arg*);}</td>
+ * </tr>
+ * <tr>
+ * <td>{@link java.lang.invoke.MethodHandles.Lookup#unreflect lookup.unreflect(aMethod)}</td>
+ * <td>({@code static})?<br>{@code T m(A*);}</td><td>{@code (T) aMethod.invoke(thisOrNull, arg*);}</td>
+ * </tr>
+ * </table>
+ *
+ * Here, the type {@code C} is the class or interface being searched for a member,
+ * documented as a parameter named {@code refc} in the lookup methods.
+ * The method type {@code MT} is composed from the return type {@code T}
+ * and the sequence of argument types {@code A*}.
+ * The constructor also has a sequence of argument types {@code A*} and
+ * is deemed to return the newly-created object of type {@code C}.
+ * Both {@code MT} and the field type {@code FT} are documented as a parameter named {@code type}.
+ * The formal parameter {@code this} stands for the self-reference of type {@code C};
+ * if it is present, it is always the leading argument to the method handle invocation.
+ * (In the case of some {@code protected} members, {@code this} may be
+ * restricted in type to the lookup class; see below.)
+ * The name {@code arg} stands for all the other method handle arguments.
+ * In the code examples for the Core Reflection API, the name {@code thisOrNull}
+ * stands for a null reference if the accessed method or field is static,
+ * and {@code this} otherwise.
+ * The names {@code aMethod}, {@code aField}, and {@code aConstructor} stand
+ * for reflective objects corresponding to the given members.
+ * <p>
+ * In cases where the given member is of variable arity (i.e., a method or constructor)
+ * the returned method handle will also be of {@linkplain MethodHandle#asVarargsCollector variable arity}.
+ * In all other cases, the returned method handle will be of fixed arity.
+ * <p style="font-size:smaller;">
+ * <em>Discussion:</em>
+ * The equivalence between looked-up method handles and underlying
+ * class members and bytecode behaviors
+ * can break down in a few ways:
+ * <ul style="font-size:smaller;">
+ * <li>If {@code C} is not symbolically accessible from the lookup class's loader,
+ * the lookup can still succeed, even when there is no equivalent
+ * Java expression or bytecoded constant.
+ * <li>Likewise, if {@code T} or {@code MT}
+ * is not symbolically accessible from the lookup class's loader,
+ * the lookup can still succeed.
+ * For example, lookups for {@code MethodHandle.invokeExact} and
+ * {@code MethodHandle.invoke} will always succeed, regardless of requested type.
+ * <li>If there is a security manager installed, it can forbid the lookup
+ * on various grounds (<a href="MethodHandles.Lookup.html#secmgr">see below</a>).
+ * By contrast, the {@code ldc} instruction on a {@code CONSTANT_MethodHandle}
+ * constant is not subject to security manager checks.
+ * <li>If the looked-up method has a
+ * <a href="MethodHandle.html#maxarity">very large arity</a>,
+ * the method handle creation may fail, due to the method handle
+ * type having too many parameters.
+ * </ul>
+ *
+ * <h1><a name="access"></a>Access checking</h1>
+ * Access checks are applied in the factory methods of {@code Lookup},
+ * when a method handle is created.
+ * This is a key difference from the Core Reflection API, since
+ * {@link java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
+ * performs access checking against every caller, on every call.
+ * <p>
+ * All access checks start from a {@code Lookup} object, which
+ * compares its recorded lookup class against all requests to
+ * create method handles.
+ * A single {@code Lookup} object can be used to create any number
+ * of access-checked method handles, all checked against a single
+ * lookup class.
+ * <p>
+ * A {@code Lookup} object can be shared with other trusted code,
+ * such as a metaobject protocol.
+ * A shared {@code Lookup} object delegates the capability
+ * to create method handles on private members of the lookup class.
+ * Even if privileged code uses the {@code Lookup} object,
+ * the access checking is confined to the privileges of the
+ * original lookup class.
+ * <p>
+ * A lookup can fail, because
+ * the containing class is not accessible to the lookup class, or
+ * because the desired class member is missing, or because the
+ * desired class member is not accessible to the lookup class, or
+ * because the lookup object is not trusted enough to access the member.
+ * In any of these cases, a {@code ReflectiveOperationException} will be
+ * thrown from the attempted lookup. The exact class will be one of
+ * the following:
+ * <ul>
+ * <li>NoSuchMethodException — if a method is requested but does not exist
+ * <li>NoSuchFieldException — if a field is requested but does not exist
+ * <li>IllegalAccessException — if the member exists but an access check fails
+ * </ul>
+ * <p>
+ * In general, the conditions under which a method handle may be
+ * looked up for a method {@code M} are no more restrictive than the conditions
+ * under which the lookup class could have compiled, verified, and resolved a call to {@code M}.
+ * Where the JVM would raise exceptions like {@code NoSuchMethodError},
+ * a method handle lookup will generally raise a corresponding
+ * checked exception, such as {@code NoSuchMethodException}.
+ * And the effect of invoking the method handle resulting from the lookup
+ * is <a href="MethodHandles.Lookup.html#equiv">exactly equivalent</a>
+ * to executing the compiled, verified, and resolved call to {@code M}.
+ * The same point is true of fields and constructors.
+ * <p style="font-size:smaller;">
+ * <em>Discussion:</em>
+ * Access checks only apply to named and reflected methods,
+ * constructors, and fields.
+ * Other method handle creation methods, such as
+ * {@link MethodHandle#asType MethodHandle.asType},
+ * do not require any access checks, and are used
+ * independently of any {@code Lookup} object.
+ * <p>
+ * If the desired member is {@code protected}, the usual JVM rules apply,
+ * including the requirement that the lookup class must be either be in the
+ * same package as the desired member, or must inherit that member.
+ * (See the Java Virtual Machine Specification, sections 4.9.2, 5.4.3.5, and 6.4.)
+ * In addition, if the desired member is a non-static field or method
+ * in a different package, the resulting method handle may only be applied
+ * to objects of the lookup class or one of its subclasses.
+ * This requirement is enforced by narrowing the type of the leading
+ * {@code this} parameter from {@code C}
+ * (which will necessarily be a superclass of the lookup class)
+ * to the lookup class itself.
+ * <p>
+ * The JVM imposes a similar requirement on {@code invokespecial} instruction,
+ * that the receiver argument must match both the resolved method <em>and</em>
+ * the current class. Again, this requirement is enforced by narrowing the
+ * type of the leading parameter to the resulting method handle.
+ * (See the Java Virtual Machine Specification, section 4.10.1.9.)
+ * <p>
+ * The JVM represents constructors and static initializer blocks as internal methods
+ * with special names ({@code "<init>"} and {@code "<clinit>"}).
+ * The internal syntax of invocation instructions allows them to refer to such internal
+ * methods as if they were normal methods, but the JVM bytecode verifier rejects them.
+ * A lookup of such an internal method will produce a {@code NoSuchMethodException}.
+ * <p>
+ * In some cases, access between nested classes is obtained by the Java compiler by creating
+ * an wrapper method to access a private method of another class
+ * in the same top-level declaration.
+ * For example, a nested class {@code C.D}
+ * can access private members within other related classes such as
+ * {@code C}, {@code C.D.E}, or {@code C.B},
+ * but the Java compiler may need to generate wrapper methods in
+ * those related classes. In such cases, a {@code Lookup} object on
+ * {@code C.E} would be unable to those private members.
+ * A workaround for this limitation is the {@link Lookup#in Lookup.in} method,
+ * which can transform a lookup on {@code C.E} into one on any of those other
+ * classes, without special elevation of privilege.
+ * <p>
+ * The accesses permitted to a given lookup object may be limited,
+ * according to its set of {@link #lookupModes lookupModes},
+ * to a subset of members normally accessible to the lookup class.
+ * For example, the {@link #publicLookup publicLookup}
+ * method produces a lookup object which is only allowed to access
+ * public members in public classes.
+ * The caller sensitive method {@link #lookup lookup}
+ * produces a lookup object with full capabilities relative to
+ * its caller class, to emulate all supported bytecode behaviors.
+ * Also, the {@link Lookup#in Lookup.in} method may produce a lookup object
+ * with fewer access modes than the original lookup object.
+ *
+ * <p style="font-size:smaller;">
+ * <a name="privacc"></a>
+ * <em>Discussion of private access:</em>
+ * We say that a lookup has <em>private access</em>
+ * if its {@linkplain #lookupModes lookup modes}
+ * include the possibility of accessing {@code private} members.
+ * As documented in the relevant methods elsewhere,
+ * only lookups with private access possess the following capabilities:
+ * <ul style="font-size:smaller;">
+ * <li>access private fields, methods, and constructors of the lookup class
+ * <li>create method handles which invoke <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a> methods,
+ * such as {@code Class.forName}
+ * <li>create method handles which {@link Lookup#findSpecial emulate invokespecial} instructions
+ * <li>avoid <a href="MethodHandles.Lookup.html#secmgr">package access checks</a>
+ * for classes accessible to the lookup class
+ * <li>create {@link Lookup#in delegated lookup objects} which have private access to other classes
+ * within the same package member
+ * </ul>
+ * <p style="font-size:smaller;">
+ * Each of these permissions is a consequence of the fact that a lookup object
+ * with private access can be securely traced back to an originating class,
+ * whose <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> and Java language access permissions
+ * can be reliably determined and emulated by method handles.
+ *
+ * <h1><a name="secmgr"></a>Security manager interactions</h1>
+ * Although bytecode instructions can only refer to classes in
+ * a related class loader, this API can search for methods in any
+ * class, as long as a reference to its {@code Class} object is
+ * available. Such cross-loader references are also possible with the
+ * Core Reflection API, and are impossible to bytecode instructions
+ * such as {@code invokestatic} or {@code getfield}.
+ * There is a {@linkplain java.lang.SecurityManager security manager API}
+ * to allow applications to check such cross-loader references.
+ * These checks apply to both the {@code MethodHandles.Lookup} API
+ * and the Core Reflection API
+ * (as found on {@link java.lang.Class Class}).
+ * <p>
+ * If a security manager is present, member lookups are subject to
+ * additional checks.
+ * From one to three calls are made to the security manager.
+ * Any of these calls can refuse access by throwing a
+ * {@link java.lang.SecurityException SecurityException}.
+ * Define {@code smgr} as the security manager,
+ * {@code lookc} as the lookup class of the current lookup object,
+ * {@code refc} as the containing class in which the member
+ * is being sought, and {@code defc} as the class in which the
+ * member is actually defined.
+ * The value {@code lookc} is defined as <em>not present</em>
+ * if the current lookup object does not have
+ * <a href="MethodHandles.Lookup.html#privacc">private access</a>.
+ * The calls are made according to the following rules:
+ * <ul>
+ * <li><b>Step 1:</b>
+ * If {@code lookc} is not present, or if its class loader is not
+ * the same as or an ancestor of the class loader of {@code refc},
+ * then {@link SecurityManager#checkPackageAccess
+ * smgr.checkPackageAccess(refcPkg)} is called,
+ * where {@code refcPkg} is the package of {@code refc}.
+ * <li><b>Step 2:</b>
+ * If the retrieved member is not public and
+ * {@code lookc} is not present, then
+ * {@link SecurityManager#checkPermission smgr.checkPermission}
+ * with {@code RuntimePermission("accessDeclaredMembers")} is called.
+ * <li><b>Step 3:</b>
+ * If the retrieved member is not public,
+ * and if {@code lookc} is not present,
+ * and if {@code defc} and {@code refc} are different,
+ * then {@link SecurityManager#checkPackageAccess
+ * smgr.checkPackageAccess(defcPkg)} is called,
+ * where {@code defcPkg} is the package of {@code defc}.
+ * </ul>
+ * Security checks are performed after other access checks have passed.
+ * Therefore, the above rules presuppose a member that is public,
+ * or else that is being accessed from a lookup class that has
+ * rights to access the member.
+ *
+ * <h1><a name="callsens"></a>Caller sensitive methods</h1>
+ * A small number of Java methods have a special property called caller sensitivity.
+ * A <em>caller-sensitive</em> method can behave differently depending on the
+ * identity of its immediate caller.
+ * <p>
+ * If a method handle for a caller-sensitive method is requested,
+ * the general rules for <a href="MethodHandles.Lookup.html#equiv">bytecode behaviors</a> apply,
+ * but they take account of the lookup class in a special way.
+ * The resulting method handle behaves as if it were called
+ * from an instruction contained in the lookup class,
+ * so that the caller-sensitive method detects the lookup class.
+ * (By contrast, the invoker of the method handle is disregarded.)
+ * Thus, in the case of caller-sensitive methods,
+ * different lookup classes may give rise to
+ * differently behaving method handles.
+ * <p>
+ * In cases where the lookup object is
+ * {@link #publicLookup publicLookup()},
+ * or some other lookup object without
+ * <a href="MethodHandles.Lookup.html#privacc">private access</a>,
+ * the lookup class is disregarded.
+ * In such cases, no caller-sensitive method handle can be created,
+ * access is forbidden, and the lookup fails with an
+ * {@code IllegalAccessException}.
+ * <p style="font-size:smaller;">
+ * <em>Discussion:</em>
+ * For example, the caller-sensitive method
+ * {@link java.lang.Class#forName(String) Class.forName(x)}
+ * can return varying classes or throw varying exceptions,
+ * depending on the class loader of the class that calls it.
+ * A public lookup of {@code Class.forName} will fail, because
+ * there is no reasonable way to determine its bytecode behavior.
+ * <p style="font-size:smaller;">
+ * If an application caches method handles for broad sharing,
+ * it should use {@code publicLookup()} to create them.
+ * If there is a lookup of {@code Class.forName}, it will fail,
+ * and the application must take appropriate action in that case.
+ * It may be that a later lookup, perhaps during the invocation of a
+ * bootstrap method, can incorporate the specific identity
+ * of the caller, making the method accessible.
+ * <p style="font-size:smaller;">
+ * The function {@code MethodHandles.lookup} is caller sensitive
+ * so that there can be a secure foundation for lookups.
+ * Nearly all other methods in the JSR 292 API rely on lookup
+ * objects to check access requests.
+ */
+ // Android-changed: Change link targets from MethodHandles#[public]Lookup to
+ // #[public]Lookup to work around complaints from javadoc.
+ public static final
+ class Lookup {
+ /** The class on behalf of whom the lookup is being performed. */
+ /* @NonNull */ private final Class<?> lookupClass;
+
+ /** The allowed sorts of members which may be looked up (PUBLIC, etc.). */
+ private final int allowedModes;
+
+ /** A single-bit mask representing {@code public} access,
+ * which may contribute to the result of {@link #lookupModes lookupModes}.
+ * The value, {@code 0x01}, happens to be the same as the value of the
+ * {@code public} {@linkplain java.lang.reflect.Modifier#PUBLIC modifier bit}.
+ */
+ public static final int PUBLIC = Modifier.PUBLIC;
+
+ /** A single-bit mask representing {@code private} access,
+ * which may contribute to the result of {@link #lookupModes lookupModes}.
+ * The value, {@code 0x02}, happens to be the same as the value of the
+ * {@code private} {@linkplain java.lang.reflect.Modifier#PRIVATE modifier bit}.
+ */
+ public static final int PRIVATE = Modifier.PRIVATE;
+
+ /** A single-bit mask representing {@code protected} access,
+ * which may contribute to the result of {@link #lookupModes lookupModes}.
+ * The value, {@code 0x04}, happens to be the same as the value of the
+ * {@code protected} {@linkplain java.lang.reflect.Modifier#PROTECTED modifier bit}.
+ */
+ public static final int PROTECTED = Modifier.PROTECTED;
+
+ /** A single-bit mask representing {@code package} access (default access),
+ * which may contribute to the result of {@link #lookupModes lookupModes}.
+ * The value is {@code 0x08}, which does not correspond meaningfully to
+ * any particular {@linkplain java.lang.reflect.Modifier modifier bit}.
+ */
+ public static final int PACKAGE = Modifier.STATIC;
+
+ private static final int ALL_MODES = (PUBLIC | PRIVATE | PROTECTED | PACKAGE);
+
+ // Android-note: Android has no notion of a trusted lookup. If required, such lookups
+ // are performed by the runtime. As a result, we always use lookupClass, which will always
+ // be non-null in our implementation.
+ //
+ // private static final int TRUSTED = -1;
+
+ private static int fixmods(int mods) {
+ mods &= (ALL_MODES - PACKAGE);
+ return (mods != 0) ? mods : PACKAGE;
+ }
+
+ /** Tells which class is performing the lookup. It is this class against
+ * which checks are performed for visibility and access permissions.
+ * <p>
+ * The class implies a maximum level of access permission,
+ * but the permissions may be additionally limited by the bitmask
+ * {@link #lookupModes lookupModes}, which controls whether non-public members
+ * can be accessed.
+ * @return the lookup class, on behalf of which this lookup object finds members
+ */
+ public Class<?> lookupClass() {
+ return lookupClass;
+ }
+
+ /** Tells which access-protection classes of members this lookup object can produce.
+ * The result is a bit-mask of the bits
+ * {@linkplain #PUBLIC PUBLIC (0x01)},
+ * {@linkplain #PRIVATE PRIVATE (0x02)},
+ * {@linkplain #PROTECTED PROTECTED (0x04)},
+ * and {@linkplain #PACKAGE PACKAGE (0x08)}.
+ * <p>
+ * A freshly-created lookup object
+ * on the {@linkplain java.lang.invoke.MethodHandles#lookup() caller's class}
+ * has all possible bits set, since the caller class can access all its own members.
+ * A lookup object on a new lookup class
+ * {@linkplain java.lang.invoke.MethodHandles.Lookup#in created from a previous lookup object}
+ * may have some mode bits set to zero.
+ * The purpose of this is to restrict access via the new lookup object,
+ * so that it can access only names which can be reached by the original
+ * lookup object, and also by the new lookup class.
+ * @return the lookup modes, which limit the kinds of access performed by this lookup object
+ */
+ public int lookupModes() {
+ return allowedModes & ALL_MODES;
+ }
+
+ /** Embody the current class (the lookupClass) as a lookup class
+ * for method handle creation.
+ * Must be called by from a method in this package,
+ * which in turn is called by a method not in this package.
+ */
+ Lookup(Class<?> lookupClass) {
+ this(lookupClass, ALL_MODES);
+ // make sure we haven't accidentally picked up a privileged class:
+ checkUnprivilegedlookupClass(lookupClass, ALL_MODES);
+ }
+
+ private Lookup(Class<?> lookupClass, int allowedModes) {
+ this.lookupClass = lookupClass;
+ this.allowedModes = allowedModes;
+ }
+
+ /**
+ * Creates a lookup on the specified new lookup class.
+ * The resulting object will report the specified
+ * class as its own {@link #lookupClass lookupClass}.
+ * <p>
+ * However, the resulting {@code Lookup} object is guaranteed
+ * to have no more access capabilities than the original.
+ * In particular, access capabilities can be lost as follows:<ul>
+ * <li>If the new lookup class differs from the old one,
+ * protected members will not be accessible by virtue of inheritance.
+ * (Protected members may continue to be accessible because of package sharing.)
+ * <li>If the new lookup class is in a different package
+ * than the old one, protected and default (package) members will not be accessible.
+ * <li>If the new lookup class is not within the same package member
+ * as the old one, private members will not be accessible.
+ * <li>If the new lookup class is not accessible to the old lookup class,
+ * then no members, not even public members, will be accessible.
+ * (In all other cases, public members will continue to be accessible.)
+ * </ul>
+ *
+ * @param requestedLookupClass the desired lookup class for the new lookup object
+ * @return a lookup object which reports the desired lookup class
+ * @throws NullPointerException if the argument is null
+ */
+ public Lookup in(Class<?> requestedLookupClass) {
+ requestedLookupClass.getClass(); // null check
+ // Android-changed: There's no notion of a trusted lookup.
+ // if (allowedModes == TRUSTED) // IMPL_LOOKUP can make any lookup at all
+ // return new Lookup(requestedLookupClass, ALL_MODES);
+
+ if (requestedLookupClass == this.lookupClass)
+ return this; // keep same capabilities
+ int newModes = (allowedModes & (ALL_MODES & ~PROTECTED));
+ if ((newModes & PACKAGE) != 0
+ && !VerifyAccess.isSamePackage(this.lookupClass, requestedLookupClass)) {
+ newModes &= ~(PACKAGE|PRIVATE);
+ }
+ // Allow nestmate lookups to be created without special privilege:
+ if ((newModes & PRIVATE) != 0
+ && !VerifyAccess.isSamePackageMember(this.lookupClass, requestedLookupClass)) {
+ newModes &= ~PRIVATE;
+ }
+ if ((newModes & PUBLIC) != 0
+ && !VerifyAccess.isClassAccessible(requestedLookupClass, this.lookupClass, allowedModes)) {
+ // The requested class it not accessible from the lookup class.
+ // No permissions.
+ newModes = 0;
+ }
+ checkUnprivilegedlookupClass(requestedLookupClass, newModes);
+ return new Lookup(requestedLookupClass, newModes);
+ }
+
+ // Make sure outer class is initialized first.
+ //
+ // Android-changed: Removed unnecessary reference to IMPL_NAMES.
+ // static { IMPL_NAMES.getClass(); }
+
+ /** Version of lookup which is trusted minimally.
+ * It can only be used to create method handles to
+ * publicly accessible members.
+ */
+ static final Lookup PUBLIC_LOOKUP = new Lookup(Object.class, PUBLIC);
+
+ /** Package-private version of lookup which is trusted. */
+ static final Lookup IMPL_LOOKUP = new Lookup(Object.class, ALL_MODES);
+
+ private static void checkUnprivilegedlookupClass(Class<?> lookupClass, int allowedModes) {
+ String name = lookupClass.getName();
+ if (name.startsWith("java.lang.invoke."))
+ throw newIllegalArgumentException("illegal lookupClass: "+lookupClass);
+
+ // For caller-sensitive MethodHandles.lookup()
+ // disallow lookup more restricted packages
+ //
+ // Android-changed: The bootstrap classloader isn't null.
+ if (allowedModes == ALL_MODES &&
+ lookupClass.getClassLoader() == Object.class.getClassLoader()) {
+ if ((name.startsWith("java.")
+ && !name.startsWith("java.io.ObjectStreamClass")
+ && !name.startsWith("java.util.concurrent.")
+ && !name.equals("java.lang.Daemons$FinalizerWatchdogDaemon")
+ && !name.equals("java.lang.runtime.ObjectMethods")
+ && !name.equals("java.lang.Thread")
+ && !name.equals("java.util.HashMap")) ||
+ (name.startsWith("sun.")
+ && !name.startsWith("sun.invoke.")
+ && !name.equals("sun.reflect.ReflectionFactory"))) {
+ throw newIllegalArgumentException("illegal lookupClass: " + lookupClass);
+ }
+ }
+ }
+
+ /**
+ * Displays the name of the class from which lookups are to be made.
+ * (The name is the one reported by {@link java.lang.Class#getName() Class.getName}.)
+ * If there are restrictions on the access permitted to this lookup,
+ * this is indicated by adding a suffix to the class name, consisting
+ * of a slash and a keyword. The keyword represents the strongest
+ * allowed access, and is chosen as follows:
+ * <ul>
+ * <li>If no access is allowed, the suffix is "/noaccess".
+ * <li>If only public access is allowed, the suffix is "/public".
+ * <li>If only public and package access are allowed, the suffix is "/package".
+ * <li>If only public, package, and private access are allowed, the suffix is "/private".
+ * </ul>
+ * If none of the above cases apply, it is the case that full
+ * access (public, package, private, and protected) is allowed.
+ * In this case, no suffix is added.
+ * This is true only of an object obtained originally from
+ * {@link java.lang.invoke.MethodHandles#lookup MethodHandles.lookup}.
+ * Objects created by {@link java.lang.invoke.MethodHandles.Lookup#in Lookup.in}
+ * always have restricted access, and will display a suffix.
+ * <p>
+ * (It may seem strange that protected access should be
+ * stronger than private access. Viewed independently from
+ * package access, protected access is the first to be lost,
+ * because it requires a direct subclass relationship between
+ * caller and callee.)
+ * @see #in
+ */
+ @Override
+ public String toString() {
+ String cname = lookupClass.getName();
+ switch (allowedModes) {
+ case 0: // no privileges
+ return cname + "/noaccess";
+ case PUBLIC:
+ return cname + "/public";
+ case PUBLIC|PACKAGE:
+ return cname + "/package";
+ case ALL_MODES & ~PROTECTED:
+ return cname + "/private";
+ case ALL_MODES:
+ return cname;
+ // Android-changed: No support for TRUSTED callers.
+ // case TRUSTED:
+ // return "/trusted"; // internal only; not exported
+ default: // Should not happen, but it's a bitfield...
+ cname = cname + "/" + Integer.toHexString(allowedModes);
+ assert(false) : cname;
+ return cname;
+ }
+ }
+
+ /**
+ * Produces a method handle for a static method.
+ * The type of the method handle will be that of the method.
+ * (Since static methods do not take receivers, there is no
+ * additional receiver argument inserted into the method handle type,
+ * as there would be with {@link #findVirtual findVirtual} or {@link #findSpecial findSpecial}.)
+ * The method and all its argument types must be accessible to the lookup object.
+ * <p>
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ * <p>
+ * If the returned method handle is invoked, the method's class will
+ * be initialized, if it has not already been initialized.
+ * <p><b>Example:</b>
+ * <blockquote><pre>{@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle MH_asList = publicLookup().findStatic(Arrays.class,
+ "asList", methodType(List.class, Object[].class));
+assertEquals("[x, y]", MH_asList.invoke("x", "y").toString());
+ * }</pre></blockquote>
+ * @param refc the class from which the method is accessed
+ * @param name the name of the method
+ * @param type the type of the method
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the method does not exist
+ * @throws IllegalAccessException if access checking fails,
+ * or if the method is not {@code static},
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ */
+ public
+ MethodHandle findStatic(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
+ Method method = refc.getDeclaredMethod(name, type.ptypes());
+ final int modifiers = method.getModifiers();
+ if (!Modifier.isStatic(modifiers)) {
+ throw new IllegalAccessException("Method" + method + " is not static");
+ }
+ checkReturnType(method, type);
+ checkAccess(refc, method.getDeclaringClass(), modifiers, method.getName());
+ return createMethodHandle(method, MethodHandle.INVOKE_STATIC, type);
+ }
+
+ private MethodHandle findVirtualForMH(String name, MethodType type) {
+ // these names require special lookups because of the implicit MethodType argument
+ if ("invoke".equals(name))
+ return invoker(type);
+ if ("invokeExact".equals(name))
+ return exactInvoker(type);
+ return null;
+ }
+
+ private MethodHandle findVirtualForVH(String name, MethodType type) {
+ VarHandle.AccessMode accessMode;
+ try {
+ accessMode = VarHandle.AccessMode.valueFromMethodName(name);
+ } catch (IllegalArgumentException e) {
+ return null;
+ }
+ return varHandleInvoker(accessMode, type);
+ }
+
+ private static MethodHandle createMethodHandle(Method method, int handleKind,
+ MethodType methodType) {
+ MethodHandle mh = new MethodHandleImpl(method.getArtMethod(), handleKind, methodType);
+ if (method.isVarArgs()) {
+ return new Transformers.VarargsCollector(mh);
+ } else {
+ return mh;
+ }
+ }
+
+ /**
+ * Produces a method handle for a virtual method.
+ * The type of the method handle will be that of the method,
+ * with the receiver type (usually {@code refc}) prepended.
+ * The method and all its argument types must be accessible to the lookup object.
+ * <p>
+ * When called, the handle will treat the first argument as a receiver
+ * and dispatch on the receiver's type to determine which method
+ * implementation to enter.
+ * (The dispatching action is identical with that performed by an
+ * {@code invokevirtual} or {@code invokeinterface} instruction.)
+ * <p>
+ * The first argument will be of type {@code refc} if the lookup
+ * class has full privileges to access the member. Otherwise
+ * the member must be {@code protected} and the first argument
+ * will be restricted in type to the lookup class.
+ * <p>
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ * <p>
+ * Because of the general <a href="MethodHandles.Lookup.html#equiv">equivalence</a> between {@code invokevirtual}
+ * instructions and method handles produced by {@code findVirtual},
+ * if the class is {@code MethodHandle} and the name string is
+ * {@code invokeExact} or {@code invoke}, the resulting
+ * method handle is equivalent to one produced by
+ * {@link java.lang.invoke.MethodHandles#exactInvoker MethodHandles.exactInvoker} or
+ * {@link java.lang.invoke.MethodHandles#invoker MethodHandles.invoker}
+ * with the same {@code type} argument.
+ *
+ * <b>Example:</b>
+ * <blockquote><pre>{@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle MH_concat = publicLookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+MethodHandle MH_hashCode = publicLookup().findVirtual(Object.class,
+ "hashCode", methodType(int.class));
+MethodHandle MH_hashCode_String = publicLookup().findVirtual(String.class,
+ "hashCode", methodType(int.class));
+assertEquals("xy", (String) MH_concat.invokeExact("x", "y"));
+assertEquals("xy".hashCode(), (int) MH_hashCode.invokeExact((Object)"xy"));
+assertEquals("xy".hashCode(), (int) MH_hashCode_String.invokeExact("xy"));
+// interface method:
+MethodHandle MH_subSequence = publicLookup().findVirtual(CharSequence.class,
+ "subSequence", methodType(CharSequence.class, int.class, int.class));
+assertEquals("def", MH_subSequence.invoke("abcdefghi", 3, 6).toString());
+// constructor "internal method" must be accessed differently:
+MethodType MT_newString = methodType(void.class); //()V for new String()
+try { assertEquals("impossible", lookup()
+ .findVirtual(String.class, "<init>", MT_newString));
+ } catch (NoSuchMethodException ex) { } // OK
+MethodHandle MH_newString = publicLookup()
+ .findConstructor(String.class, MT_newString);
+assertEquals("", (String) MH_newString.invokeExact());
+ * }</pre></blockquote>
+ *
+ * @param refc the class or interface from which the method is accessed
+ * @param name the name of the method
+ * @param type the type of the method, with the receiver argument omitted
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the method does not exist
+ * @throws IllegalAccessException if access checking fails,
+ * or if the method is {@code static}
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findVirtual(Class<?> refc, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
+ // Special case : when we're looking up a virtual method on the MethodHandles class
+ // itself, we can return one of our specialized invokers.
+ if (refc == MethodHandle.class) {
+ MethodHandle mh = findVirtualForMH(name, type);
+ if (mh != null) {
+ return mh;
+ }
+ } else if (refc == VarHandle.class) {
+ // Returns an non-exact invoker.
+ MethodHandle mh = findVirtualForVH(name, type);
+ if (mh != null) {
+ return mh;
+ }
+ }
+
+ Method method = refc.getInstanceMethod(name, type.ptypes());
+ if (method == null) {
+ // This is pretty ugly and a consequence of the MethodHandles API. We have to throw
+ // an IAE and not an NSME if the method exists but is static (even though the RI's
+ // IAE has a message that says "no such method"). We confine the ugliness and
+ // slowness to the failure case, and allow getInstanceMethod to remain fairly
+ // general.
+ try {
+ Method m = refc.getDeclaredMethod(name, type.ptypes());
+ if (Modifier.isStatic(m.getModifiers())) {
+ throw new IllegalAccessException("Method" + m + " is static");
+ }
+ } catch (NoSuchMethodException ignored) {
+ }
+
+ throw new NoSuchMethodException(name + " " + Arrays.toString(type.ptypes()));
+ }
+ checkReturnType(method, type);
+
+ // We have a valid method, perform access checks.
+ checkAccess(refc, method.getDeclaringClass(), method.getModifiers(), method.getName());
+
+ // Insert the leading reference parameter.
+ MethodType handleType = type.insertParameterTypes(0, refc);
+ return createMethodHandle(method, MethodHandle.INVOKE_VIRTUAL, handleType);
+ }
+
+ /**
+ * Produces a method handle which creates an object and initializes it, using
+ * the constructor of the specified type.
+ * The parameter types of the method handle will be those of the constructor,
+ * while the return type will be a reference to the constructor's class.
+ * The constructor and all its argument types must be accessible to the lookup object.
+ * <p>
+ * The requested type must have a return type of {@code void}.
+ * (This is consistent with the JVM's treatment of constructor type descriptors.)
+ * <p>
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
+ * <p>
+ * If the returned method handle is invoked, the constructor's class will
+ * be initialized, if it has not already been initialized.
+ * <p><b>Example:</b>
+ * <blockquote><pre>{@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle MH_newArrayList = publicLookup().findConstructor(
+ ArrayList.class, methodType(void.class, Collection.class));
+Collection orig = Arrays.asList("x", "y");
+Collection copy = (ArrayList) MH_newArrayList.invokeExact(orig);
+assert(orig != copy);
+assertEquals(orig, copy);
+// a variable-arity constructor:
+MethodHandle MH_newProcessBuilder = publicLookup().findConstructor(
+ ProcessBuilder.class, methodType(void.class, String[].class));
+ProcessBuilder pb = (ProcessBuilder)
+ MH_newProcessBuilder.invoke("x", "y", "z");
+assertEquals("[x, y, z]", pb.command().toString());
+ * }</pre></blockquote>
+ * @param refc the class or interface from which the method is accessed
+ * @param type the type of the method, with the receiver argument omitted, and a void return type
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the constructor does not exist
+ * @throws IllegalAccessException if access checking fails
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findConstructor(Class<?> refc, MethodType type) throws NoSuchMethodException, IllegalAccessException {
+ if (refc.isArray()) {
+ throw new NoSuchMethodException("no constructor for array class: " + refc.getName());
+ }
+ // The queried |type| is (PT1,PT2,..)V
+ Constructor constructor = refc.getDeclaredConstructor(type.ptypes());
+ if (constructor == null) {
+ throw new NoSuchMethodException(
+ "No constructor for " + constructor.getDeclaringClass() + " matching " + type);
+ }
+ checkAccess(refc, constructor.getDeclaringClass(), constructor.getModifiers(),
+ constructor.getName());
+
+ return createMethodHandleForConstructor(constructor);
+ }
+
+ // BEGIN Android-added: Add findClass(String) from OpenJDK 17. http://b/270028670
+ // TODO: Unhide this method.
+ /**
+ * Looks up a class by name from the lookup context defined by this {@code Lookup} object,
+ * <a href="MethodHandles.Lookup.html#equiv">as if resolved</a> by an {@code ldc} instruction.
+ * Such a resolution, as specified in JVMS 5.4.3.1 section, attempts to locate and load the class,
+ * and then determines whether the class is accessible to this lookup object.
+ * <p>
+ * The lookup context here is determined by the {@linkplain #lookupClass() lookup class},
+ * its class loader, and the {@linkplain #lookupModes() lookup modes}.
+ *
+ * @param targetName the fully qualified name of the class to be looked up.
+ * @return the requested class.
+ * @throws SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws LinkageError if the linkage fails
+ * @throws ClassNotFoundException if the class cannot be loaded by the lookup class' loader.
+ * @throws IllegalAccessException if the class is not accessible, using the allowed access
+ * modes.
+ * @throws NullPointerException if {@code targetName} is null
+ * @since 9
+ * @jvms 5.4.3.1 Class and Interface Resolution
+ * @hide
+ */
+ public Class<?> findClass(String targetName) throws ClassNotFoundException, IllegalAccessException {
+ Class<?> targetClass = Class.forName(targetName, false, lookupClass.getClassLoader());
+ return accessClass(targetClass);
+ }
+ // END Android-added: Add findClass(String) from OpenJDK 17. http://b/270028670
+
+ private MethodHandle createMethodHandleForConstructor(Constructor constructor) {
+ Class<?> refc = constructor.getDeclaringClass();
+ MethodType constructorType =
+ MethodType.methodType(refc, constructor.getParameterTypes());
+ MethodHandle mh;
+ if (refc == String.class) {
+ // String constructors have optimized StringFactory methods
+ // that matches returned type. These factory methods combine the
+ // memory allocation and initialization calls for String objects.
+ mh = new MethodHandleImpl(constructor.getArtMethod(), MethodHandle.INVOKE_DIRECT,
+ constructorType);
+ } else {
+ // Constructors for all other classes use a Construct transformer to perform
+ // their memory allocation and call to <init>.
+ MethodType initType = initMethodType(constructorType);
+ MethodHandle initHandle = new MethodHandleImpl(
+ constructor.getArtMethod(), MethodHandle.INVOKE_DIRECT, initType);
+ mh = new Transformers.Construct(initHandle, constructorType);
+ }
+
+ if (constructor.isVarArgs()) {
+ mh = new Transformers.VarargsCollector(mh);
+ }
+ return mh;
+ }
+
+ private static MethodType initMethodType(MethodType constructorType) {
+ // Returns a MethodType appropriate for class <init>
+ // methods. Constructor MethodTypes have the form
+ // (PT1,PT2,...)C and class <init> MethodTypes have the
+ // form (C,PT1,PT2,...)V.
+ assert constructorType.rtype() != void.class;
+
+ // Insert constructorType C as the first parameter type in
+ // the MethodType for <init>.
+ Class<?> [] initPtypes = new Class<?> [constructorType.ptypes().length + 1];
+ initPtypes[0] = constructorType.rtype();
+ System.arraycopy(constructorType.ptypes(), 0, initPtypes, 1,
+ constructorType.ptypes().length);
+
+ // Set the return type for the <init> MethodType to be void.
+ return MethodType.methodType(void.class, initPtypes);
+ }
+
+ // BEGIN Android-added: Add accessClass(Class) from OpenJDK 17. http://b/270028670
+ /*
+ * Returns IllegalAccessException due to access violation to the given targetClass.
+ *
+ * This method is called by {@link Lookup#accessClass} and {@link Lookup#ensureInitialized}
+ * which verifies access to a class rather a member.
+ */
+ private IllegalAccessException makeAccessException(Class<?> targetClass) {
+ String message = "access violation: "+ targetClass;
+ if (this == MethodHandles.publicLookup()) {
+ message += ", from public Lookup";
+ } else {
+ // Android-changed: Remove unsupported module name.
+ // Module m = lookupClass().getModule();
+ // message += ", from " + lookupClass() + " (" + m + ")";
+ message += ", from " + lookupClass();
+ // Android-removed: Remove prevLookupClass until supported by Lookup in OpenJDK 17.
+ // if (prevLookupClass != null) {
+ // message += ", previous lookup " +
+ // prevLookupClass.getName() + " (" + prevLookupClass.getModule() + ")";
+ // }
+ }
+ return new IllegalAccessException(message);
+ }
+
+ // TODO: Unhide this method.
+ /**
+ * Determines if a class can be accessed from the lookup context defined by
+ * this {@code Lookup} object. The static initializer of the class is not run.
+ * If {@code targetClass} is an array class, {@code targetClass} is accessible
+ * if the element type of the array class is accessible. Otherwise,
+ * {@code targetClass} is determined as accessible as follows.
+ *
+ * <p>
+ * If {@code targetClass} is in the same module as the lookup class,
+ * the lookup class is {@code LC} in module {@code M1} and
+ * the previous lookup class is in module {@code M0} or
+ * {@code null} if not present,
+ * {@code targetClass} is accessible if and only if one of the following is true:
+ * <ul>
+ * <li>If this lookup has {@link #PRIVATE} access, {@code targetClass} is
+ * {@code LC} or other class in the same nest of {@code LC}.</li>
+ * <li>If this lookup has {@link #PACKAGE} access, {@code targetClass} is
+ * in the same runtime package of {@code LC}.</li>
+ * <li>If this lookup has {@link #MODULE} access, {@code targetClass} is
+ * a public type in {@code M1}.</li>
+ * <li>If this lookup has {@link #PUBLIC} access, {@code targetClass} is
+ * a public type in a package exported by {@code M1} to at least {@code M0}
+ * if the previous lookup class is present; otherwise, {@code targetClass}
+ * is a public type in a package exported by {@code M1} unconditionally.</li>
+ * </ul>
+ *
+ * <p>
+ * Otherwise, if this lookup has {@link #UNCONDITIONAL} access, this lookup
+ * can access public types in all modules when the type is in a package
+ * that is exported unconditionally.
+ * <p>
+ * Otherwise, {@code targetClass} is in a different module from {@code lookupClass},
+ * and if this lookup does not have {@code PUBLIC} access, {@code lookupClass}
+ * is inaccessible.
+ * <p>
+ * Otherwise, if this lookup has no {@linkplain #previousLookupClass() previous lookup class},
+ * {@code M1} is the module containing {@code lookupClass} and
+ * {@code M2} is the module containing {@code targetClass},
+ * then {@code targetClass} is accessible if and only if
+ * <ul>
+ * <li>{@code M1} reads {@code M2}, and
+ * <li>{@code targetClass} is public and in a package exported by
+ * {@code M2} at least to {@code M1}.
+ * </ul>
+ * <p>
+ * Otherwise, if this lookup has a {@linkplain #previousLookupClass() previous lookup class},
+ * {@code M1} and {@code M2} are as before, and {@code M0} is the module
+ * containing the previous lookup class, then {@code targetClass} is accessible
+ * if and only if one of the following is true:
+ * <ul>
+ * <li>{@code targetClass} is in {@code M0} and {@code M1}
+ * {@linkplain Module#reads reads} {@code M0} and the type is
+ * in a package that is exported to at least {@code M1}.
+ * <li>{@code targetClass} is in {@code M1} and {@code M0}
+ * {@linkplain Module#reads reads} {@code M1} and the type is
+ * in a package that is exported to at least {@code M0}.
+ * <li>{@code targetClass} is in a third module {@code M2} and both {@code M0}
+ * and {@code M1} reads {@code M2} and the type is in a package
+ * that is exported to at least both {@code M0} and {@code M2}.
+ * </ul>
+ * <p>
+ * Otherwise, {@code targetClass} is not accessible.
+ *
+ * @param targetClass the class to be access-checked
+ * @return the class that has been access-checked
+ * @throws IllegalAccessException if the class is not accessible from the lookup class
+ * and previous lookup class, if present, using the allowed access modes.
+ * @throws SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if {@code targetClass} is {@code null}
+ * @since 9
+ * @see <a href="#cross-module-lookup">Cross-module lookups</a>
+ * @hide
+ */
+ public Class<?> accessClass(Class<?> targetClass) throws IllegalAccessException {
+ if (!isClassAccessible(targetClass)) {
+ throw makeAccessException(targetClass);
+ }
+ // Android-removed: SecurityManager is unnecessary on Android.
+ // checkSecurityManager(targetClass);
+ return targetClass;
+ }
+
+ boolean isClassAccessible(Class<?> refc) {
+ Objects.requireNonNull(refc);
+ Class<?> caller = lookupClassOrNull();
+ Class<?> type = refc;
+ while (type.isArray()) {
+ type = type.getComponentType();
+ }
+ // Android-removed: Remove prevLookupClass until supported by Lookup in OpenJDK 17.
+ // return caller == null || VerifyAccess.isClassAccessible(type, caller, prevLookupClass, allowedModes);
+ return caller == null || VerifyAccess.isClassAccessible(type, caller, allowedModes);
+ }
+
+ // This is just for calling out to MethodHandleImpl.
+ private Class<?> lookupClassOrNull() {
+ // Android-changed: Android always returns lookupClass and has no concept of TRUSTED.
+ // return (allowedModes == TRUSTED) ? null : lookupClass;
+ return lookupClass;
+ }
+ // END Android-added: Add accessClass(Class) from OpenJDK 17. http://b/270028670
+
+ /**
+ * Produces an early-bound method handle for a virtual method.
+ * It will bypass checks for overriding methods on the receiver,
+ * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
+ * instruction from within the explicitly specified {@code specialCaller}.
+ * The type of the method handle will be that of the method,
+ * with a suitably restricted receiver type prepended.
+ * (The receiver type will be {@code specialCaller} or a subtype.)
+ * The method and all its argument types must be accessible
+ * to the lookup object.
+ * <p>
+ * Before method resolution,
+ * if the explicitly specified caller class is not identical with the
+ * lookup class, or if this lookup object does not have
+ * <a href="MethodHandles.Lookup.html#privacc">private access</a>
+ * privileges, the access fails.
+ * <p>
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ * <p style="font-size:smaller;">
+ * <em>(Note: JVM internal methods named {@code "<init>"} are not visible to this API,
+ * even though the {@code invokespecial} instruction can refer to them
+ * in special circumstances. Use {@link #findConstructor findConstructor}
+ * to access instance initialization methods in a safe manner.)</em>
+ * <p><b>Example:</b>
+ * <blockquote><pre>{@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+static class Listie extends ArrayList {
+ public String toString() { return "[wee Listie]"; }
+ static Lookup lookup() { return MethodHandles.lookup(); }
+}
+...
+// no access to constructor via invokeSpecial:
+MethodHandle MH_newListie = Listie.lookup()
+ .findConstructor(Listie.class, methodType(void.class));
+Listie l = (Listie) MH_newListie.invokeExact();
+try { assertEquals("impossible", Listie.lookup().findSpecial(
+ Listie.class, "<init>", methodType(void.class), Listie.class));
+ } catch (NoSuchMethodException ex) { } // OK
+// access to super and self methods via invokeSpecial:
+MethodHandle MH_super = Listie.lookup().findSpecial(
+ ArrayList.class, "toString" , methodType(String.class), Listie.class);
+MethodHandle MH_this = Listie.lookup().findSpecial(
+ Listie.class, "toString" , methodType(String.class), Listie.class);
+MethodHandle MH_duper = Listie.lookup().findSpecial(
+ Object.class, "toString" , methodType(String.class), Listie.class);
+assertEquals("[]", (String) MH_super.invokeExact(l));
+assertEquals(""+l, (String) MH_this.invokeExact(l));
+assertEquals("[]", (String) MH_duper.invokeExact(l)); // ArrayList method
+try { assertEquals("inaccessible", Listie.lookup().findSpecial(
+ String.class, "toString", methodType(String.class), Listie.class));
+ } catch (IllegalAccessException ex) { } // OK
+Listie subl = new Listie() { public String toString() { return "[subclass]"; } };
+assertEquals(""+l, (String) MH_this.invokeExact(subl)); // Listie method
+ * }</pre></blockquote>
+ *
+ * @param refc the class or interface from which the method is accessed
+ * @param name the name of the method (which must not be "<init>")
+ * @param type the type of the method, with the receiver argument omitted
+ * @param specialCaller the proposed calling class to perform the {@code invokespecial}
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the method does not exist
+ * @throws IllegalAccessException if access checking fails
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findSpecial(Class<?> refc, String name, MethodType type,
+ Class<?> specialCaller) throws NoSuchMethodException, IllegalAccessException {
+ if (specialCaller == null) {
+ throw new NullPointerException("specialCaller == null");
+ }
+
+ if (type == null) {
+ throw new NullPointerException("type == null");
+ }
+
+ if (name == null) {
+ throw new NullPointerException("name == null");
+ }
+
+ if (refc == null) {
+ throw new NullPointerException("ref == null");
+ }
+
+ // Make sure that the special caller is identical to the lookup class or that we have
+ // private access.
+ // Android-changed: Also allow access to any interface methods.
+ checkSpecialCaller(specialCaller, refc);
+
+ // Even though constructors are invoked using a "special" invoke, handles to them can't
+ // be created using findSpecial. Callers must use findConstructor instead. Similarly,
+ // there is no path for calling static class initializers.
+ if (name.startsWith("<")) {
+ throw new NoSuchMethodException(name + " is not a valid method name.");
+ }
+
+ Method method = refc.getDeclaredMethod(name, type.ptypes());
+ checkReturnType(method, type);
+ return findSpecial(method, type, refc, specialCaller);
+ }
+
+ private MethodHandle findSpecial(Method method, MethodType type,
+ Class<?> refc, Class<?> specialCaller)
+ throws IllegalAccessException {
+ if (Modifier.isStatic(method.getModifiers())) {
+ throw new IllegalAccessException("expected a non-static method:" + method);
+ }
+
+ if (Modifier.isPrivate(method.getModifiers())) {
+ // Since this is a private method, we'll need to also make sure that the
+ // lookup class is the same as the refering class. We've already checked that
+ // the specialCaller is the same as the special lookup class, both of these must
+ // be the same as the declaring class(*) in order to access the private method.
+ //
+ // (*) Well, this isn't true for nested classes but OpenJDK doesn't support those
+ // either.
+ if (refc != lookupClass()) {
+ throw new IllegalAccessException("no private access for invokespecial : "
+ + refc + ", from" + this);
+ }
+
+ // This is a private method, so there's nothing special to do.
+ MethodType handleType = type.insertParameterTypes(0, refc);
+ return createMethodHandle(method, MethodHandle.INVOKE_DIRECT, handleType);
+ }
+
+ // This is a public, protected or package-private method, which means we're expecting
+ // invoke-super semantics. We'll have to restrict the receiver type appropriately on the
+ // handle once we check that there really is a "super" relationship between them.
+ if (!method.getDeclaringClass().isAssignableFrom(specialCaller)) {
+ throw new IllegalAccessException(refc + "is not assignable from " + specialCaller);
+ }
+
+ // Note that we restrict the receiver to "specialCaller" instances.
+ MethodType handleType = type.insertParameterTypes(0, specialCaller);
+ return createMethodHandle(method, MethodHandle.INVOKE_SUPER, handleType);
+ }
+
+ /**
+ * Produces a method handle giving read access to a non-static field.
+ * The type of the method handle will have a return type of the field's
+ * value type.
+ * The method handle's single argument will be the instance containing
+ * the field.
+ * Access checking is performed immediately on behalf of the lookup class.
+ * @param refc the class or interface from which the method is accessed
+ * @param name the field's name
+ * @param type the field's type
+ * @return a method handle which can load values from the field
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
+ return findAccessor(refc, name, type, MethodHandle.IGET);
+ }
+
+ private MethodHandle findAccessor(Class<?> refc, String name, Class<?> type, int kind)
+ throws NoSuchFieldException, IllegalAccessException {
+ final Field field = findFieldOfType(refc, name, type);
+ return findAccessor(field, refc, type, kind, true /* performAccessChecks */);
+ }
+
+ private MethodHandle findAccessor(Field field, Class<?> refc, Class<?> type, int kind,
+ boolean performAccessChecks)
+ throws IllegalAccessException {
+ final boolean isSetterKind = kind == MethodHandle.IPUT || kind == MethodHandle.SPUT;
+ final boolean isStaticKind = kind == MethodHandle.SGET || kind == MethodHandle.SPUT;
+ commonFieldChecks(field, refc, type, isStaticKind, performAccessChecks);
+ if (performAccessChecks) {
+ final int modifiers = field.getModifiers();
+ if (isSetterKind && Modifier.isFinal(modifiers)) {
+ throw new IllegalAccessException("Field " + field + " is final");
+ }
+ }
+
+ final MethodType methodType;
+ switch (kind) {
+ case MethodHandle.SGET:
+ methodType = MethodType.methodType(type);
+ break;
+ case MethodHandle.SPUT:
+ methodType = MethodType.methodType(void.class, type);
+ break;
+ case MethodHandle.IGET:
+ methodType = MethodType.methodType(type, refc);
+ break;
+ case MethodHandle.IPUT:
+ methodType = MethodType.methodType(void.class, refc, type);
+ break;
+ default:
+ throw new IllegalArgumentException("Invalid kind " + kind);
+ }
+ return new MethodHandleImpl(field.getArtField(), kind, methodType);
+ }
+
+ /**
+ * Produces a method handle giving write access to a non-static field.
+ * The type of the method handle will have a void return type.
+ * The method handle will take two arguments, the instance containing
+ * the field, and the value to be stored.
+ * The second argument will be of the field's value type.
+ * Access checking is performed immediately on behalf of the lookup class.
+ * @param refc the class or interface from which the method is accessed
+ * @param name the field's name
+ * @param type the field's type
+ * @return a method handle which can store values into the field
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
+ return findAccessor(refc, name, type, MethodHandle.IPUT);
+ }
+
+ // BEGIN Android-changed: OpenJDK 9+181 VarHandle API factory method.
+ /**
+ * Produces a VarHandle giving access to a non-static field {@code name}
+ * of type {@code type} declared in a class of type {@code recv}.
+ * The VarHandle's variable type is {@code type} and it has one
+ * coordinate type, {@code recv}.
+ * <p>
+ * Access checking is performed immediately on behalf of the lookup
+ * class.
+ * <p>
+ * Certain access modes of the returned VarHandle are unsupported under
+ * the following conditions:
+ * <ul>
+ * <li>if the field is declared {@code final}, then the write, atomic
+ * update, numeric atomic update, and bitwise atomic update access
+ * modes are unsupported.
+ * <li>if the field type is anything other than {@code byte},
+ * {@code short}, {@code char}, {@code int}, {@code long},
+ * {@code float}, or {@code double} then numeric atomic update
+ * access modes are unsupported.
+ * <li>if the field type is anything other than {@code boolean},
+ * {@code byte}, {@code short}, {@code char}, {@code int} or
+ * {@code long} then bitwise atomic update access modes are
+ * unsupported.
+ * </ul>
+ * <p>
+ * If the field is declared {@code volatile} then the returned VarHandle
+ * will override access to the field (effectively ignore the
+ * {@code volatile} declaration) in accordance to its specified
+ * access modes.
+ * <p>
+ * If the field type is {@code float} or {@code double} then numeric
+ * and atomic update access modes compare values using their bitwise
+ * representation (see {@link Float#floatToRawIntBits} and
+ * {@link Double#doubleToRawLongBits}, respectively).
+ * @apiNote
+ * Bitwise comparison of {@code float} values or {@code double} values,
+ * as performed by the numeric and atomic update access modes, differ
+ * from the primitive {@code ==} operator and the {@link Float#equals}
+ * and {@link Double#equals} methods, specifically with respect to
+ * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
+ * Care should be taken when performing a compare and set or a compare
+ * and exchange operation with such values since the operation may
+ * unexpectedly fail.
+ * There are many possible NaN values that are considered to be
+ * {@code NaN} in Java, although no IEEE 754 floating-point operation
+ * provided by Java can distinguish between them. Operation failure can
+ * occur if the expected or witness value is a NaN value and it is
+ * transformed (perhaps in a platform specific manner) into another NaN
+ * value, and thus has a different bitwise representation (see
+ * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
+ * details).
+ * The values {@code -0.0} and {@code +0.0} have different bitwise
+ * representations but are considered equal when using the primitive
+ * {@code ==} operator. Operation failure can occur if, for example, a
+ * numeric algorithm computes an expected value to be say {@code -0.0}
+ * and previously computed the witness value to be say {@code +0.0}.
+ * @param recv the receiver class, of type {@code R}, that declares the
+ * non-static field
+ * @param name the field's name
+ * @param type the field's type, of type {@code T}
+ * @return a VarHandle giving access to non-static fields.
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ * @since 9
+ */
+ public VarHandle findVarHandle(Class<?> recv, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
+ final Field field = findFieldOfType(recv, name, type);
+ final boolean isStatic = false;
+ final boolean performAccessChecks = true;
+ commonFieldChecks(field, recv, type, isStatic, performAccessChecks);
+ return FieldVarHandle.create(field);
+ }
+ // END Android-changed: OpenJDK 9+181 VarHandle API factory method.
+
+ // BEGIN Android-added: Common field resolution and access check methods.
+ private Field findFieldOfType(final Class<?> refc, String name, Class<?> type)
+ throws NoSuchFieldException {
+ Field field = null;
+
+ // Search refc and super classes for the field.
+ for (Class<?> cls = refc; cls != null; cls = cls.getSuperclass()) {
+ try {
+ field = cls.getDeclaredField(name);
+ break;
+ } catch (NoSuchFieldException e) {
+ }
+ }
+
+ if (field == null) {
+ // Force failure citing refc.
+ field = refc.getDeclaredField(name);
+ }
+
+ final Class<?> fieldType = field.getType();
+ if (fieldType != type) {
+ throw new NoSuchFieldException(name);
+ }
+ return field;
+ }
+
+ private void commonFieldChecks(Field field, Class<?> refc, Class<?> type,
+ boolean isStatic, boolean performAccessChecks)
+ throws IllegalAccessException {
+ final int modifiers = field.getModifiers();
+ if (performAccessChecks) {
+ checkAccess(refc, field.getDeclaringClass(), modifiers, field.getName());
+ }
+ if (Modifier.isStatic(modifiers) != isStatic) {
+ String reason = "Field " + field + " is " +
+ (isStatic ? "not " : "") + "static";
+ throw new IllegalAccessException(reason);
+ }
+ }
+ // END Android-added: Common field resolution and access check methods.
+
+ /**
+ * Produces a method handle giving read access to a static field.
+ * The type of the method handle will have a return type of the field's
+ * value type.
+ * The method handle will take no arguments.
+ * Access checking is performed immediately on behalf of the lookup class.
+ * <p>
+ * If the returned method handle is invoked, the field's class will
+ * be initialized, if it has not already been initialized.
+ * @param refc the class or interface from which the method is accessed
+ * @param name the field's name
+ * @param type the field's type
+ * @return a method handle which can load values from the field
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findStaticGetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
+ return findAccessor(refc, name, type, MethodHandle.SGET);
+ }
+
+ /**
+ * Produces a method handle giving write access to a static field.
+ * The type of the method handle will have a void return type.
+ * The method handle will take a single
+ * argument, of the field's value type, the value to be stored.
+ * Access checking is performed immediately on behalf of the lookup class.
+ * <p>
+ * If the returned method handle is invoked, the field's class will
+ * be initialized, if it has not already been initialized.
+ * @param refc the class or interface from which the method is accessed
+ * @param name the field's name
+ * @param type the field's type
+ * @return a method handle which can store values into the field
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle findStaticSetter(Class<?> refc, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
+ return findAccessor(refc, name, type, MethodHandle.SPUT);
+ }
+
+ // BEGIN Android-changed: OpenJDK 9+181 VarHandle API factory method.
+ /**
+ * Produces a VarHandle giving access to a static field {@code name} of
+ * type {@code type} declared in a class of type {@code decl}.
+ * The VarHandle's variable type is {@code type} and it has no
+ * coordinate types.
+ * <p>
+ * Access checking is performed immediately on behalf of the lookup
+ * class.
+ * <p>
+ * If the returned VarHandle is operated on, the declaring class will be
+ * initialized, if it has not already been initialized.
+ * <p>
+ * Certain access modes of the returned VarHandle are unsupported under
+ * the following conditions:
+ * <ul>
+ * <li>if the field is declared {@code final}, then the write, atomic
+ * update, numeric atomic update, and bitwise atomic update access
+ * modes are unsupported.
+ * <li>if the field type is anything other than {@code byte},
+ * {@code short}, {@code char}, {@code int}, {@code long},
+ * {@code float}, or {@code double}, then numeric atomic update
+ * access modes are unsupported.
+ * <li>if the field type is anything other than {@code boolean},
+ * {@code byte}, {@code short}, {@code char}, {@code int} or
+ * {@code long} then bitwise atomic update access modes are
+ * unsupported.
+ * </ul>
+ * <p>
+ * If the field is declared {@code volatile} then the returned VarHandle
+ * will override access to the field (effectively ignore the
+ * {@code volatile} declaration) in accordance to its specified
+ * access modes.
+ * <p>
+ * If the field type is {@code float} or {@code double} then numeric
+ * and atomic update access modes compare values using their bitwise
+ * representation (see {@link Float#floatToRawIntBits} and
+ * {@link Double#doubleToRawLongBits}, respectively).
+ * @apiNote
+ * Bitwise comparison of {@code float} values or {@code double} values,
+ * as performed by the numeric and atomic update access modes, differ
+ * from the primitive {@code ==} operator and the {@link Float#equals}
+ * and {@link Double#equals} methods, specifically with respect to
+ * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
+ * Care should be taken when performing a compare and set or a compare
+ * and exchange operation with such values since the operation may
+ * unexpectedly fail.
+ * There are many possible NaN values that are considered to be
+ * {@code NaN} in Java, although no IEEE 754 floating-point operation
+ * provided by Java can distinguish between them. Operation failure can
+ * occur if the expected or witness value is a NaN value and it is
+ * transformed (perhaps in a platform specific manner) into another NaN
+ * value, and thus has a different bitwise representation (see
+ * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
+ * details).
+ * The values {@code -0.0} and {@code +0.0} have different bitwise
+ * representations but are considered equal when using the primitive
+ * {@code ==} operator. Operation failure can occur if, for example, a
+ * numeric algorithm computes an expected value to be say {@code -0.0}
+ * and previously computed the witness value to be say {@code +0.0}.
+ * @param decl the class that declares the static field
+ * @param name the field's name
+ * @param type the field's type, of type {@code T}
+ * @return a VarHandle giving access to a static field
+ * @throws NoSuchFieldException if the field does not exist
+ * @throws IllegalAccessException if access checking fails, or if the field is not {@code static}
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ * @since 9
+ */
+ public VarHandle findStaticVarHandle(Class<?> decl, String name, Class<?> type) throws NoSuchFieldException, IllegalAccessException {
+ final Field field = findFieldOfType(decl, name, type);
+ final boolean isStatic = true;
+ final boolean performAccessChecks = true;
+ commonFieldChecks(field, decl, type, isStatic, performAccessChecks);
+ return StaticFieldVarHandle.create(field);
+ }
+ // END Android-changed: OpenJDK 9+181 VarHandle API factory method.
+
+ /**
+ * Produces an early-bound method handle for a non-static method.
+ * The receiver must have a supertype {@code defc} in which a method
+ * of the given name and type is accessible to the lookup class.
+ * The method and all its argument types must be accessible to the lookup object.
+ * The type of the method handle will be that of the method,
+ * without any insertion of an additional receiver parameter.
+ * The given receiver will be bound into the method handle,
+ * so that every call to the method handle will invoke the
+ * requested method on the given receiver.
+ * <p>
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set
+ * <em>and</em> the trailing array argument is not the only argument.
+ * (If the trailing array argument is the only argument,
+ * the given receiver value will be bound to it.)
+ * <p>
+ * This is equivalent to the following code:
+ * <blockquote><pre>{@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle mh0 = lookup().findVirtual(defc, name, type);
+MethodHandle mh1 = mh0.bindTo(receiver);
+MethodType mt1 = mh1.type();
+if (mh0.isVarargsCollector())
+ mh1 = mh1.asVarargsCollector(mt1.parameterType(mt1.parameterCount()-1));
+return mh1;
+ * }</pre></blockquote>
+ * where {@code defc} is either {@code receiver.getClass()} or a super
+ * type of that class, in which the requested method is accessible
+ * to the lookup class.
+ * (Note that {@code bindTo} does not preserve variable arity.)
+ * @param receiver the object from which the method is accessed
+ * @param name the name of the method
+ * @param type the type of the method, with the receiver argument omitted
+ * @return the desired method handle
+ * @throws NoSuchMethodException if the method does not exist
+ * @throws IllegalAccessException if access checking fails
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws NullPointerException if any argument is null
+ * @see MethodHandle#bindTo
+ * @see #findVirtual
+ */
+ public MethodHandle bind(Object receiver, String name, MethodType type) throws NoSuchMethodException, IllegalAccessException {
+ MethodHandle handle = findVirtual(receiver.getClass(), name, type);
+ MethodHandle adapter = handle.bindTo(receiver);
+ MethodType adapterType = adapter.type();
+ if (handle.isVarargsCollector()) {
+ adapter = adapter.asVarargsCollector(
+ adapterType.parameterType(adapterType.parameterCount() - 1));
+ }
+
+ return adapter;
+ }
+
+ /**
+ * Makes a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
+ * to <i>m</i>, if the lookup class has permission.
+ * If <i>m</i> is non-static, the receiver argument is treated as an initial argument.
+ * If <i>m</i> is virtual, overriding is respected on every call.
+ * Unlike the Core Reflection API, exceptions are <em>not</em> wrapped.
+ * The type of the method handle will be that of the method,
+ * with the receiver type prepended (but only if it is non-static).
+ * If the method's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class.
+ * If <i>m</i> is not public, do not share the resulting handle with untrusted parties.
+ * <p>
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ * <p>
+ * If <i>m</i> is static, and
+ * if the returned method handle is invoked, the method's class will
+ * be initialized, if it has not already been initialized.
+ * @param m the reflected method
+ * @return a method handle which can invoke the reflected method
+ * @throws IllegalAccessException if access checking fails
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @throws NullPointerException if the argument is null
+ */
+ public MethodHandle unreflect(Method m) throws IllegalAccessException {
+ if (m == null) {
+ throw new NullPointerException("m == null");
+ }
+
+ MethodType methodType = MethodType.methodType(m.getReturnType(),
+ m.getParameterTypes());
+
+ // We should only perform access checks if setAccessible hasn't been called yet.
+ if (!m.isAccessible()) {
+ checkAccess(m.getDeclaringClass(), m.getDeclaringClass(), m.getModifiers(),
+ m.getName());
+ }
+
+ if (Modifier.isStatic(m.getModifiers())) {
+ return createMethodHandle(m, MethodHandle.INVOKE_STATIC, methodType);
+ } else {
+ methodType = methodType.insertParameterTypes(0, m.getDeclaringClass());
+ return createMethodHandle(m, MethodHandle.INVOKE_VIRTUAL, methodType);
+ }
+ }
+
+ /**
+ * Produces a method handle for a reflected method.
+ * It will bypass checks for overriding methods on the receiver,
+ * <a href="MethodHandles.Lookup.html#equiv">as if called</a> from an {@code invokespecial}
+ * instruction from within the explicitly specified {@code specialCaller}.
+ * The type of the method handle will be that of the method,
+ * with a suitably restricted receiver type prepended.
+ * (The receiver type will be {@code specialCaller} or a subtype.)
+ * If the method's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class,
+ * as if {@code invokespecial} instruction were being linked.
+ * <p>
+ * Before method resolution,
+ * if the explicitly specified caller class is not identical with the
+ * lookup class, or if this lookup object does not have
+ * <a href="MethodHandles.Lookup.html#privacc">private access</a>
+ * privileges, the access fails.
+ * <p>
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the method's variable arity modifier bit ({@code 0x0080}) is set.
+ * @param m the reflected method
+ * @param specialCaller the class nominally calling the method
+ * @return a method handle which can invoke the reflected method
+ * @throws IllegalAccessException if access checking fails
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @throws NullPointerException if any argument is null
+ */
+ public MethodHandle unreflectSpecial(Method m, Class<?> specialCaller) throws IllegalAccessException {
+ if (m == null) {
+ throw new NullPointerException("m == null");
+ }
+
+ if (specialCaller == null) {
+ throw new NullPointerException("specialCaller == null");
+ }
+
+ if (!m.isAccessible()) {
+ // Android-changed: Match Java language 9 behavior where unreflectSpecial continues
+ // to require exact caller lookupClass match.
+ checkSpecialCaller(specialCaller, null);
+ }
+
+ final MethodType methodType = MethodType.methodType(m.getReturnType(),
+ m.getParameterTypes());
+ return findSpecial(m, methodType, m.getDeclaringClass() /* refc */, specialCaller);
+ }
+
+ /**
+ * Produces a method handle for a reflected constructor.
+ * The type of the method handle will be that of the constructor,
+ * with the return type changed to the declaring class.
+ * The method handle will perform a {@code newInstance} operation,
+ * creating a new instance of the constructor's class on the
+ * arguments passed to the method handle.
+ * <p>
+ * If the constructor's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class.
+ * <p>
+ * The returned method handle will have
+ * {@linkplain MethodHandle#asVarargsCollector variable arity} if and only if
+ * the constructor's variable arity modifier bit ({@code 0x0080}) is set.
+ * <p>
+ * If the returned method handle is invoked, the constructor's class will
+ * be initialized, if it has not already been initialized.
+ * @param c the reflected constructor
+ * @return a method handle which can invoke the reflected constructor
+ * @throws IllegalAccessException if access checking fails
+ * or if the method's variable arity modifier bit
+ * is set and {@code asVarargsCollector} fails
+ * @throws NullPointerException if the argument is null
+ */
+ public MethodHandle unreflectConstructor(Constructor<?> c) throws IllegalAccessException {
+ if (c == null) {
+ throw new NullPointerException("c == null");
+ }
+
+ if (!c.isAccessible()) {
+ checkAccess(c.getDeclaringClass(), c.getDeclaringClass(), c.getModifiers(),
+ c.getName());
+ }
+
+ return createMethodHandleForConstructor(c);
+ }
+
+ /**
+ * Produces a method handle giving read access to a reflected field.
+ * The type of the method handle will have a return type of the field's
+ * value type.
+ * If the field is static, the method handle will take no arguments.
+ * Otherwise, its single argument will be the instance containing
+ * the field.
+ * If the field's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class.
+ * <p>
+ * If the field is static, and
+ * if the returned method handle is invoked, the field's class will
+ * be initialized, if it has not already been initialized.
+ * @param f the reflected field
+ * @return a method handle which can load values from the reflected field
+ * @throws IllegalAccessException if access checking fails
+ * @throws NullPointerException if the argument is null
+ */
+ public MethodHandle unreflectGetter(Field f) throws IllegalAccessException {
+ return findAccessor(f, f.getDeclaringClass(), f.getType(),
+ Modifier.isStatic(f.getModifiers()) ? MethodHandle.SGET : MethodHandle.IGET,
+ !f.isAccessible() /* performAccessChecks */);
+ }
+
+ /**
+ * Produces a method handle giving write access to a reflected field.
+ * The type of the method handle will have a void return type.
+ * If the field is static, the method handle will take a single
+ * argument, of the field's value type, the value to be stored.
+ * Otherwise, the two arguments will be the instance containing
+ * the field, and the value to be stored.
+ * If the field's {@code accessible} flag is not set,
+ * access checking is performed immediately on behalf of the lookup class.
+ * <p>
+ * If the field is static, and
+ * if the returned method handle is invoked, the field's class will
+ * be initialized, if it has not already been initialized.
+ * @param f the reflected field
+ * @return a method handle which can store values into the reflected field
+ * @throws IllegalAccessException if access checking fails
+ * @throws NullPointerException if the argument is null
+ */
+ public MethodHandle unreflectSetter(Field f) throws IllegalAccessException {
+ return findAccessor(f, f.getDeclaringClass(), f.getType(),
+ Modifier.isStatic(f.getModifiers()) ? MethodHandle.SPUT : MethodHandle.IPUT,
+ !f.isAccessible() /* performAccessChecks */);
+ }
+
+ // BEGIN Android-changed: OpenJDK 9+181 VarHandle API factory method.
+ /**
+ * Produces a VarHandle giving access to a reflected field {@code f}
+ * of type {@code T} declared in a class of type {@code R}.
+ * The VarHandle's variable type is {@code T}.
+ * If the field is non-static the VarHandle has one coordinate type,
+ * {@code R}. Otherwise, the field is static, and the VarHandle has no
+ * coordinate types.
+ * <p>
+ * Access checking is performed immediately on behalf of the lookup
+ * class, regardless of the value of the field's {@code accessible}
+ * flag.
+ * <p>
+ * If the field is static, and if the returned VarHandle is operated
+ * on, the field's declaring class will be initialized, if it has not
+ * already been initialized.
+ * <p>
+ * Certain access modes of the returned VarHandle are unsupported under
+ * the following conditions:
+ * <ul>
+ * <li>if the field is declared {@code final}, then the write, atomic
+ * update, numeric atomic update, and bitwise atomic update access
+ * modes are unsupported.
+ * <li>if the field type is anything other than {@code byte},
+ * {@code short}, {@code char}, {@code int}, {@code long},
+ * {@code float}, or {@code double} then numeric atomic update
+ * access modes are unsupported.
+ * <li>if the field type is anything other than {@code boolean},
+ * {@code byte}, {@code short}, {@code char}, {@code int} or
+ * {@code long} then bitwise atomic update access modes are
+ * unsupported.
+ * </ul>
+ * <p>
+ * If the field is declared {@code volatile} then the returned VarHandle
+ * will override access to the field (effectively ignore the
+ * {@code volatile} declaration) in accordance to its specified
+ * access modes.
+ * <p>
+ * If the field type is {@code float} or {@code double} then numeric
+ * and atomic update access modes compare values using their bitwise
+ * representation (see {@link Float#floatToRawIntBits} and
+ * {@link Double#doubleToRawLongBits}, respectively).
+ * @apiNote
+ * Bitwise comparison of {@code float} values or {@code double} values,
+ * as performed by the numeric and atomic update access modes, differ
+ * from the primitive {@code ==} operator and the {@link Float#equals}
+ * and {@link Double#equals} methods, specifically with respect to
+ * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
+ * Care should be taken when performing a compare and set or a compare
+ * and exchange operation with such values since the operation may
+ * unexpectedly fail.
+ * There are many possible NaN values that are considered to be
+ * {@code NaN} in Java, although no IEEE 754 floating-point operation
+ * provided by Java can distinguish between them. Operation failure can
+ * occur if the expected or witness value is a NaN value and it is
+ * transformed (perhaps in a platform specific manner) into another NaN
+ * value, and thus has a different bitwise representation (see
+ * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
+ * details).
+ * The values {@code -0.0} and {@code +0.0} have different bitwise
+ * representations but are considered equal when using the primitive
+ * {@code ==} operator. Operation failure can occur if, for example, a
+ * numeric algorithm computes an expected value to be say {@code -0.0}
+ * and previously computed the witness value to be say {@code +0.0}.
+ * @param f the reflected field, with a field of type {@code T}, and
+ * a declaring class of type {@code R}
+ * @return a VarHandle giving access to non-static fields or a static
+ * field
+ * @throws IllegalAccessException if access checking fails
+ * @throws NullPointerException if the argument is null
+ * @since 9
+ */
+ public VarHandle unreflectVarHandle(Field f) throws IllegalAccessException {
+ final boolean isStatic = Modifier.isStatic(f.getModifiers());
+ final boolean performAccessChecks = true;
+ commonFieldChecks(f, f.getDeclaringClass(), f.getType(), isStatic, performAccessChecks);
+ return isStatic ? StaticFieldVarHandle.create(f) : FieldVarHandle.create(f);
+ }
+ // END Android-changed: OpenJDK 9+181 VarHandle API factory method.
+
+ /**
+ * Cracks a <a href="MethodHandleInfo.html#directmh">direct method handle</a>
+ * created by this lookup object or a similar one.
+ * Security and access checks are performed to ensure that this lookup object
+ * is capable of reproducing the target method handle.
+ * This means that the cracking may fail if target is a direct method handle
+ * but was created by an unrelated lookup object.
+ * This can happen if the method handle is <a href="MethodHandles.Lookup.html#callsens">caller sensitive</a>
+ * and was created by a lookup object for a different class.
+ * @param target a direct method handle to crack into symbolic reference components
+ * @return a symbolic reference which can be used to reconstruct this method handle from this lookup object
+ * @exception SecurityException if a security manager is present and it
+ * <a href="MethodHandles.Lookup.html#secmgr">refuses access</a>
+ * @throws IllegalArgumentException if the target is not a direct method handle or if access checking fails
+ * @exception NullPointerException if the target is {@code null}
+ * @see MethodHandleInfo
+ * @since 1.8
+ */
+ public MethodHandleInfo revealDirect(MethodHandle target) {
+ MethodHandleImpl directTarget = getMethodHandleImpl(target);
+ MethodHandleInfo info = directTarget.reveal();
+
+ try {
+ checkAccess(lookupClass(), info.getDeclaringClass(), info.getModifiers(),
+ info.getName());
+ } catch (IllegalAccessException exception) {
+ throw new IllegalArgumentException("Unable to access memeber.", exception);
+ }
+
+ return info;
+ }
+
+ private boolean hasPrivateAccess() {
+ return (allowedModes & PRIVATE) != 0;
+ }
+
+ /** Check public/protected/private bits on the symbolic reference class and its member. */
+ void checkAccess(Class<?> refc, Class<?> defc, int mods, String methName)
+ throws IllegalAccessException {
+ int allowedModes = this.allowedModes;
+
+ if (Modifier.isProtected(mods) &&
+ defc == Object.class &&
+ "clone".equals(methName) &&
+ refc.isArray()) {
+ // The JVM does this hack also.
+ // (See ClassVerifier::verify_invoke_instructions
+ // and LinkResolver::check_method_accessability.)
+ // Because the JVM does not allow separate methods on array types,
+ // there is no separate method for int[].clone.
+ // All arrays simply inherit Object.clone.
+ // But for access checking logic, we make Object.clone
+ // (normally protected) appear to be public.
+ // Later on, when the DirectMethodHandle is created,
+ // its leading argument will be restricted to the
+ // requested array type.
+ // N.B. The return type is not adjusted, because
+ // that is *not* the bytecode behavior.
+ mods ^= Modifier.PROTECTED | Modifier.PUBLIC;
+ }
+
+ if (Modifier.isProtected(mods) && Modifier.isConstructor(mods)) {
+ // cannot "new" a protected ctor in a different package
+ mods ^= Modifier.PROTECTED;
+ }
+
+ if (Modifier.isPublic(mods) && Modifier.isPublic(refc.getModifiers()) && allowedModes != 0)
+ return; // common case
+ int requestedModes = fixmods(mods); // adjust 0 => PACKAGE
+ if ((requestedModes & allowedModes) != 0) {
+ if (VerifyAccess.isMemberAccessible(refc, defc, mods, lookupClass(), allowedModes))
+ return;
+ } else {
+ // Protected members can also be checked as if they were package-private.
+ if ((requestedModes & PROTECTED) != 0 && (allowedModes & PACKAGE) != 0
+ && VerifyAccess.isSamePackage(defc, lookupClass()))
+ return;
+ }
+
+ throwMakeAccessException(accessFailedMessage(refc, defc, mods), this);
+ }
+
+ String accessFailedMessage(Class<?> refc, Class<?> defc, int mods) {
+ // check the class first:
+ boolean classOK = (Modifier.isPublic(defc.getModifiers()) &&
+ (defc == refc ||
+ Modifier.isPublic(refc.getModifiers())));
+ if (!classOK && (allowedModes & PACKAGE) != 0) {
+ classOK = (VerifyAccess.isClassAccessible(defc, lookupClass(), ALL_MODES) &&
+ (defc == refc ||
+ VerifyAccess.isClassAccessible(refc, lookupClass(), ALL_MODES)));
+ }
+ if (!classOK)
+ return "class is not public";
+ if (Modifier.isPublic(mods))
+ return "access to public member failed"; // (how?)
+ if (Modifier.isPrivate(mods))
+ return "member is private";
+ if (Modifier.isProtected(mods))
+ return "member is protected";
+ return "member is private to package";
+ }
+
+ // Android-changed: checkSpecialCaller assumes that ALLOW_NESTMATE_ACCESS = false,
+ // as in upstream OpenJDK.
+ //
+ // private static final boolean ALLOW_NESTMATE_ACCESS = false;
+
+ // Android-changed: Match java language 9 behavior allowing special access if the reflected
+ // class (called 'refc', the class from which the method is being accessed) is an interface
+ // and is implemented by the caller.
+ private void checkSpecialCaller(Class<?> specialCaller, Class<?> refc) throws IllegalAccessException {
+ // Android-changed: No support for TRUSTED lookups. Also construct the
+ // IllegalAccessException by hand because the upstream code implicitly assumes
+ // that the lookupClass == specialCaller.
+ //
+ // if (allowedModes == TRUSTED) return;
+ boolean isInterfaceLookup = (refc != null &&
+ refc.isInterface() &&
+ refc.isAssignableFrom(specialCaller));
+ if (!hasPrivateAccess() || (specialCaller != lookupClass() && !isInterfaceLookup)) {
+ throw new IllegalAccessException("no private access for invokespecial : "
+ + specialCaller + ", from" + this);
+ }
+ }
+
+ private void throwMakeAccessException(String message, Object from) throws
+ IllegalAccessException{
+ message = message + ": "+ toString();
+ if (from != null) message += ", from " + from;
+ throw new IllegalAccessException(message);
+ }
+
+ private void checkReturnType(Method method, MethodType methodType)
+ throws NoSuchMethodException {
+ if (method.getReturnType() != methodType.rtype()) {
+ throw new NoSuchMethodException(method.getName() + methodType);
+ }
+ }
+ }
+
+ /**
+ * "Cracks" {@code target} to reveal the underlying {@code MethodHandleImpl}.
+ */
+ private static MethodHandleImpl getMethodHandleImpl(MethodHandle target) {
+ // Special case : We implement handles to constructors as transformers,
+ // so we must extract the underlying handle from the transformer.
+ if (target instanceof Transformers.Construct) {
+ target = ((Transformers.Construct) target).getConstructorHandle();
+ }
+
+ // Special case: Var-args methods are also implemented as Transformers,
+ // so we should get the underlying handle in that case as well.
+ if (target instanceof Transformers.VarargsCollector) {
+ target = target.asFixedArity();
+ }
+
+ if (target instanceof MethodHandleImpl) {
+ return (MethodHandleImpl) target;
+ }
+
+ throw new IllegalArgumentException(target + " is not a direct handle");
+ }
+
+ // Android-removed: unsupported @jvms tag in doc-comment.
+ /**
+ * Produces a method handle constructing arrays of a desired type,
+ * as if by the {@code anewarray} bytecode.
+ * The return type of the method handle will be the array type.
+ * The type of its sole argument will be {@code int}, which specifies the size of the array.
+ *
+ * <p> If the returned method handle is invoked with a negative
+ * array size, a {@code NegativeArraySizeException} will be thrown.
+ *
+ * @param arrayClass an array type
+ * @return a method handle which can create arrays of the given type
+ * @throws NullPointerException if the argument is {@code null}
+ * @throws IllegalArgumentException if {@code arrayClass} is not an array type
+ * @see java.lang.reflect.Array#newInstance(Class, int)
+ * @since 9
+ */
+ public static
+ MethodHandle arrayConstructor(Class<?> arrayClass) throws IllegalArgumentException {
+ if (!arrayClass.isArray()) {
+ throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
+ }
+ // Android-changed: transformer based implementation.
+ // MethodHandle ani = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_Array_newInstance).
+ // bindTo(arrayClass.getComponentType());
+ // return ani.asType(ani.type().changeReturnType(arrayClass))
+ return new Transformers.ArrayConstructor(arrayClass);
+ }
+
+ // Android-removed: unsupported @jvms tag in doc-comment.
+ /**
+ * Produces a method handle returning the length of an array,
+ * as if by the {@code arraylength} bytecode.
+ * The type of the method handle will have {@code int} as return type,
+ * and its sole argument will be the array type.
+ *
+ * <p> If the returned method handle is invoked with a {@code null}
+ * array reference, a {@code NullPointerException} will be thrown.
+ *
+ * @param arrayClass an array type
+ * @return a method handle which can retrieve the length of an array of the given array type
+ * @throws NullPointerException if the argument is {@code null}
+ * @throws IllegalArgumentException if arrayClass is not an array type
+ * @since 9
+ */
+ public static
+ MethodHandle arrayLength(Class<?> arrayClass) throws IllegalArgumentException {
+ // Android-changed: transformer based implementation.
+ // return MethodHandleImpl.makeArrayElementAccessor(arrayClass, MethodHandleImpl.ArrayAccess.LENGTH);
+ if (!arrayClass.isArray()) {
+ throw newIllegalArgumentException("not an array class: " + arrayClass.getName());
+ }
+ return new Transformers.ArrayLength(arrayClass);
+ }
+
+ // BEGIN Android-added: method to check if a class is an array.
+ private static void checkClassIsArray(Class<?> c) {
+ if (!c.isArray()) {
+ throw new IllegalArgumentException("Not an array type: " + c);
+ }
+ }
+
+ private static void checkTypeIsViewable(Class<?> componentType) {
+ if (componentType == short.class ||
+ componentType == char.class ||
+ componentType == int.class ||
+ componentType == long.class ||
+ componentType == float.class ||
+ componentType == double.class) {
+ return;
+ }
+ throw new UnsupportedOperationException("Component type not supported: " + componentType);
+ }
+ // END Android-added: method to check if a class is an array.
+
+ /**
+ * Produces a method handle giving read access to elements of an array.
+ * The type of the method handle will have a return type of the array's
+ * element type. Its first argument will be the array type,
+ * and the second will be {@code int}.
+ * @param arrayClass an array type
+ * @return a method handle which can load values from the given array type
+ * @throws NullPointerException if the argument is null
+ * @throws IllegalArgumentException if arrayClass is not an array type
+ */
+ public static
+ MethodHandle arrayElementGetter(Class<?> arrayClass) throws IllegalArgumentException {
+ checkClassIsArray(arrayClass);
+ final Class<?> componentType = arrayClass.getComponentType();
+ if (componentType.isPrimitive()) {
+ try {
+ return Lookup.PUBLIC_LOOKUP.findStatic(MethodHandles.class,
+ "arrayElementGetter",
+ MethodType.methodType(componentType, arrayClass, int.class));
+ } catch (NoSuchMethodException | IllegalAccessException exception) {
+ throw new AssertionError(exception);
+ }
+ }
+
+ return new Transformers.ReferenceArrayElementGetter(arrayClass);
+ }
+
+ /** @hide */ public static byte arrayElementGetter(byte[] array, int i) { return array[i]; }
+ /** @hide */ public static boolean arrayElementGetter(boolean[] array, int i) { return array[i]; }
+ /** @hide */ public static char arrayElementGetter(char[] array, int i) { return array[i]; }
+ /** @hide */ public static short arrayElementGetter(short[] array, int i) { return array[i]; }
+ /** @hide */ public static int arrayElementGetter(int[] array, int i) { return array[i]; }
+ /** @hide */ public static long arrayElementGetter(long[] array, int i) { return array[i]; }
+ /** @hide */ public static float arrayElementGetter(float[] array, int i) { return array[i]; }
+ /** @hide */ public static double arrayElementGetter(double[] array, int i) { return array[i]; }
+
+ /**
+ * Produces a method handle giving write access to elements of an array.
+ * The type of the method handle will have a void return type.
+ * Its last argument will be the array's element type.
+ * The first and second arguments will be the array type and int.
+ * @param arrayClass the class of an array
+ * @return a method handle which can store values into the array type
+ * @throws NullPointerException if the argument is null
+ * @throws IllegalArgumentException if arrayClass is not an array type
+ */
+ public static
+ MethodHandle arrayElementSetter(Class<?> arrayClass) throws IllegalArgumentException {
+ checkClassIsArray(arrayClass);
+ final Class<?> componentType = arrayClass.getComponentType();
+ if (componentType.isPrimitive()) {
+ try {
+ return Lookup.PUBLIC_LOOKUP.findStatic(MethodHandles.class,
+ "arrayElementSetter",
+ MethodType.methodType(void.class, arrayClass, int.class, componentType));
+ } catch (NoSuchMethodException | IllegalAccessException exception) {
+ throw new AssertionError(exception);
+ }
+ }
+
+ return new Transformers.ReferenceArrayElementSetter(arrayClass);
+ }
+
+ /** @hide */
+ public static void arrayElementSetter(byte[] array, int i, byte val) { array[i] = val; }
+ /** @hide */
+ public static void arrayElementSetter(boolean[] array, int i, boolean val) { array[i] = val; }
+ /** @hide */
+ public static void arrayElementSetter(char[] array, int i, char val) { array[i] = val; }
+ /** @hide */
+ public static void arrayElementSetter(short[] array, int i, short val) { array[i] = val; }
+ /** @hide */
+ public static void arrayElementSetter(int[] array, int i, int val) { array[i] = val; }
+ /** @hide */
+ public static void arrayElementSetter(long[] array, int i, long val) { array[i] = val; }
+ /** @hide */
+ public static void arrayElementSetter(float[] array, int i, float val) { array[i] = val; }
+ /** @hide */
+ public static void arrayElementSetter(double[] array, int i, double val) { array[i] = val; }
+
+ // BEGIN Android-changed: OpenJDK 9+181 VarHandle API factory methods.
+ /**
+ * Produces a VarHandle giving access to elements of an array of type
+ * {@code arrayClass}. The VarHandle's variable type is the component type
+ * of {@code arrayClass} and the list of coordinate types is
+ * {@code (arrayClass, int)}, where the {@code int} coordinate type
+ * corresponds to an argument that is an index into an array.
+ * <p>
+ * Certain access modes of the returned VarHandle are unsupported under
+ * the following conditions:
+ * <ul>
+ * <li>if the component type is anything other than {@code byte},
+ * {@code short}, {@code char}, {@code int}, {@code long},
+ * {@code float}, or {@code double} then numeric atomic update access
+ * modes are unsupported.
+ * <li>if the field type is anything other than {@code boolean},
+ * {@code byte}, {@code short}, {@code char}, {@code int} or
+ * {@code long} then bitwise atomic update access modes are
+ * unsupported.
+ * </ul>
+ * <p>
+ * If the component type is {@code float} or {@code double} then numeric
+ * and atomic update access modes compare values using their bitwise
+ * representation (see {@link Float#floatToRawIntBits} and
+ * {@link Double#doubleToRawLongBits}, respectively).
+ * @apiNote
+ * Bitwise comparison of {@code float} values or {@code double} values,
+ * as performed by the numeric and atomic update access modes, differ
+ * from the primitive {@code ==} operator and the {@link Float#equals}
+ * and {@link Double#equals} methods, specifically with respect to
+ * comparing NaN values or comparing {@code -0.0} with {@code +0.0}.
+ * Care should be taken when performing a compare and set or a compare
+ * and exchange operation with such values since the operation may
+ * unexpectedly fail.
+ * There are many possible NaN values that are considered to be
+ * {@code NaN} in Java, although no IEEE 754 floating-point operation
+ * provided by Java can distinguish between them. Operation failure can
+ * occur if the expected or witness value is a NaN value and it is
+ * transformed (perhaps in a platform specific manner) into another NaN
+ * value, and thus has a different bitwise representation (see
+ * {@link Float#intBitsToFloat} or {@link Double#longBitsToDouble} for more
+ * details).
+ * The values {@code -0.0} and {@code +0.0} have different bitwise
+ * representations but are considered equal when using the primitive
+ * {@code ==} operator. Operation failure can occur if, for example, a
+ * numeric algorithm computes an expected value to be say {@code -0.0}
+ * and previously computed the witness value to be say {@code +0.0}.
+ * @param arrayClass the class of an array, of type {@code T[]}
+ * @return a VarHandle giving access to elements of an array
+ * @throws NullPointerException if the arrayClass is null
+ * @throws IllegalArgumentException if arrayClass is not an array type
+ * @since 9
+ */
+ public static
+ VarHandle arrayElementVarHandle(Class<?> arrayClass) throws IllegalArgumentException {
+ checkClassIsArray(arrayClass);
+ return ArrayElementVarHandle.create(arrayClass);
+ }
+
+ /**
+ * Produces a VarHandle giving access to elements of a {@code byte[]} array
+ * viewed as if it were a different primitive array type, such as
+ * {@code int[]} or {@code long[]}.
+ * The VarHandle's variable type is the component type of
+ * {@code viewArrayClass} and the list of coordinate types is
+ * {@code (byte[], int)}, where the {@code int} coordinate type
+ * corresponds to an argument that is an index into a {@code byte[]} array.
+ * The returned VarHandle accesses bytes at an index in a {@code byte[]}
+ * array, composing bytes to or from a value of the component type of
+ * {@code viewArrayClass} according to the given endianness.
+ * <p>
+ * The supported component types (variables types) are {@code short},
+ * {@code char}, {@code int}, {@code long}, {@code float} and
+ * {@code double}.
+ * <p>
+ * Access of bytes at a given index will result in an
+ * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
+ * or greater than the {@code byte[]} array length minus the size (in bytes)
+ * of {@code T}.
+ * <p>
+ * Access of bytes at an index may be aligned or misaligned for {@code T},
+ * with respect to the underlying memory address, {@code A} say, associated
+ * with the array and index.
+ * If access is misaligned then access for anything other than the
+ * {@code get} and {@code set} access modes will result in an
+ * {@code IllegalStateException}. In such cases atomic access is only
+ * guaranteed with respect to the largest power of two that divides the GCD
+ * of {@code A} and the size (in bytes) of {@code T}.
+ * If access is aligned then following access modes are supported and are
+ * guaranteed to support atomic access:
+ * <ul>
+ * <li>read write access modes for all {@code T}, with the exception of
+ * access modes {@code get} and {@code set} for {@code long} and
+ * {@code double} on 32-bit platforms.
+ * <li>atomic update access modes for {@code int}, {@code long},
+ * {@code float} or {@code double}.
+ * (Future major platform releases of the JDK may support additional
+ * types for certain currently unsupported access modes.)
+ * <li>numeric atomic update access modes for {@code int} and {@code long}.
+ * (Future major platform releases of the JDK may support additional
+ * numeric types for certain currently unsupported access modes.)
+ * <li>bitwise atomic update access modes for {@code int} and {@code long}.
+ * (Future major platform releases of the JDK may support additional
+ * numeric types for certain currently unsupported access modes.)
+ * </ul>
+ * <p>
+ * Misaligned access, and therefore atomicity guarantees, may be determined
+ * for {@code byte[]} arrays without operating on a specific array. Given
+ * an {@code index}, {@code T} and it's corresponding boxed type,
+ * {@code T_BOX}, misalignment may be determined as follows:
+ * <pre>{@code
+ * int sizeOfT = T_BOX.BYTES; // size in bytes of T
+ * int misalignedAtZeroIndex = ByteBuffer.wrap(new byte[0]).
+ * alignmentOffset(0, sizeOfT);
+ * int misalignedAtIndex = (misalignedAtZeroIndex + index) % sizeOfT;
+ * boolean isMisaligned = misalignedAtIndex != 0;
+ * }</pre>
+ * <p>
+ * If the variable type is {@code float} or {@code double} then atomic
+ * update access modes compare values using their bitwise representation
+ * (see {@link Float#floatToRawIntBits} and
+ * {@link Double#doubleToRawLongBits}, respectively).
+ * @param viewArrayClass the view array class, with a component type of
+ * type {@code T}
+ * @param byteOrder the endianness of the view array elements, as
+ * stored in the underlying {@code byte} array
+ * @return a VarHandle giving access to elements of a {@code byte[]} array
+ * viewed as if elements corresponding to the components type of the view
+ * array class
+ * @throws NullPointerException if viewArrayClass or byteOrder is null
+ * @throws IllegalArgumentException if viewArrayClass is not an array type
+ * @throws UnsupportedOperationException if the component type of
+ * viewArrayClass is not supported as a variable type
+ * @since 9
+ */
+ public static
+ VarHandle byteArrayViewVarHandle(Class<?> viewArrayClass,
+ ByteOrder byteOrder) throws IllegalArgumentException {
+ checkClassIsArray(viewArrayClass);
+ checkTypeIsViewable(viewArrayClass.getComponentType());
+ return ByteArrayViewVarHandle.create(viewArrayClass, byteOrder);
+ }
+
+ /**
+ * Produces a VarHandle giving access to elements of a {@code ByteBuffer}
+ * viewed as if it were an array of elements of a different primitive
+ * component type to that of {@code byte}, such as {@code int[]} or
+ * {@code long[]}.
+ * The VarHandle's variable type is the component type of
+ * {@code viewArrayClass} and the list of coordinate types is
+ * {@code (ByteBuffer, int)}, where the {@code int} coordinate type
+ * corresponds to an argument that is an index into a {@code byte[]} array.
+ * The returned VarHandle accesses bytes at an index in a
+ * {@code ByteBuffer}, composing bytes to or from a value of the component
+ * type of {@code viewArrayClass} according to the given endianness.
+ * <p>
+ * The supported component types (variables types) are {@code short},
+ * {@code char}, {@code int}, {@code long}, {@code float} and
+ * {@code double}.
+ * <p>
+ * Access will result in a {@code ReadOnlyBufferException} for anything
+ * other than the read access modes if the {@code ByteBuffer} is read-only.
+ * <p>
+ * Access of bytes at a given index will result in an
+ * {@code IndexOutOfBoundsException} if the index is less than {@code 0}
+ * or greater than the {@code ByteBuffer} limit minus the size (in bytes) of
+ * {@code T}.
+ * <p>
+ * Access of bytes at an index may be aligned or misaligned for {@code T},
+ * with respect to the underlying memory address, {@code A} say, associated
+ * with the {@code ByteBuffer} and index.
+ * If access is misaligned then access for anything other than the
+ * {@code get} and {@code set} access modes will result in an
+ * {@code IllegalStateException}. In such cases atomic access is only
+ * guaranteed with respect to the largest power of two that divides the GCD
+ * of {@code A} and the size (in bytes) of {@code T}.
+ * If access is aligned then following access modes are supported and are
+ * guaranteed to support atomic access:
+ * <ul>
+ * <li>read write access modes for all {@code T}, with the exception of
+ * access modes {@code get} and {@code set} for {@code long} and
+ * {@code double} on 32-bit platforms.
+ * <li>atomic update access modes for {@code int}, {@code long},
+ * {@code float} or {@code double}.
+ * (Future major platform releases of the JDK may support additional
+ * types for certain currently unsupported access modes.)
+ * <li>numeric atomic update access modes for {@code int} and {@code long}.
+ * (Future major platform releases of the JDK may support additional
+ * numeric types for certain currently unsupported access modes.)
+ * <li>bitwise atomic update access modes for {@code int} and {@code long}.
+ * (Future major platform releases of the JDK may support additional
+ * numeric types for certain currently unsupported access modes.)
+ * </ul>
+ * <p>
+ * Misaligned access, and therefore atomicity guarantees, may be determined
+ * for a {@code ByteBuffer}, {@code bb} (direct or otherwise), an
+ * {@code index}, {@code T} and it's corresponding boxed type,
+ * {@code T_BOX}, as follows:
+ * <pre>{@code
+ * int sizeOfT = T_BOX.BYTES; // size in bytes of T
+ * ByteBuffer bb = ...
+ * int misalignedAtIndex = bb.alignmentOffset(index, sizeOfT);
+ * boolean isMisaligned = misalignedAtIndex != 0;
+ * }</pre>
+ * <p>
+ * If the variable type is {@code float} or {@code double} then atomic
+ * update access modes compare values using their bitwise representation
+ * (see {@link Float#floatToRawIntBits} and
+ * {@link Double#doubleToRawLongBits}, respectively).
+ * @param viewArrayClass the view array class, with a component type of
+ * type {@code T}
+ * @param byteOrder the endianness of the view array elements, as
+ * stored in the underlying {@code ByteBuffer} (Note this overrides the
+ * endianness of a {@code ByteBuffer})
+ * @return a VarHandle giving access to elements of a {@code ByteBuffer}
+ * viewed as if elements corresponding to the components type of the view
+ * array class
+ * @throws NullPointerException if viewArrayClass or byteOrder is null
+ * @throws IllegalArgumentException if viewArrayClass is not an array type
+ * @throws UnsupportedOperationException if the component type of
+ * viewArrayClass is not supported as a variable type
+ * @since 9
+ */
+ public static
+ VarHandle byteBufferViewVarHandle(Class<?> viewArrayClass,
+ ByteOrder byteOrder) throws IllegalArgumentException {
+ checkClassIsArray(viewArrayClass);
+ checkTypeIsViewable(viewArrayClass.getComponentType());
+ return ByteBufferViewVarHandle.create(viewArrayClass, byteOrder);
+ }
+ // END Android-changed: OpenJDK 9+181 VarHandle API factory methods.
+
+ /// method handle invocation (reflective style)
+
+ /**
+ * Produces a method handle which will invoke any method handle of the
+ * given {@code type}, with a given number of trailing arguments replaced by
+ * a single trailing {@code Object[]} array.
+ * The resulting invoker will be a method handle with the following
+ * arguments:
+ * <ul>
+ * <li>a single {@code MethodHandle} target
+ * <li>zero or more leading values (counted by {@code leadingArgCount})
+ * <li>an {@code Object[]} array containing trailing arguments
+ * </ul>
+ * <p>
+ * The invoker will invoke its target like a call to {@link MethodHandle#invoke invoke} with
+ * the indicated {@code type}.
+ * That is, if the target is exactly of the given {@code type}, it will behave
+ * like {@code invokeExact}; otherwise it behave as if {@link MethodHandle#asType asType}
+ * is used to convert the target to the required {@code type}.
+ * <p>
+ * The type of the returned invoker will not be the given {@code type}, but rather
+ * will have all parameters except the first {@code leadingArgCount}
+ * replaced by a single array of type {@code Object[]}, which will be
+ * the final parameter.
+ * <p>
+ * Before invoking its target, the invoker will spread the final array, apply
+ * reference casts as necessary, and unbox and widen primitive arguments.
+ * If, when the invoker is called, the supplied array argument does
+ * not have the correct number of elements, the invoker will throw
+ * an {@link IllegalArgumentException} instead of invoking the target.
+ * <p>
+ * This method is equivalent to the following code (though it may be more efficient):
+ * <blockquote><pre>{@code
+MethodHandle invoker = MethodHandles.invoker(type);
+int spreadArgCount = type.parameterCount() - leadingArgCount;
+invoker = invoker.asSpreader(Object[].class, spreadArgCount);
+return invoker;
+ * }</pre></blockquote>
+ * This method throws no reflective or security exceptions.
+ * @param type the desired target type
+ * @param leadingArgCount number of fixed arguments, to be passed unchanged to the target
+ * @return a method handle suitable for invoking any method handle of the given type
+ * @throws NullPointerException if {@code type} is null
+ * @throws IllegalArgumentException if {@code leadingArgCount} is not in
+ * the range from 0 to {@code type.parameterCount()} inclusive,
+ * or if the resulting method handle's type would have
+ * <a href="MethodHandle.html#maxarity">too many parameters</a>
+ */
+ static public
+ MethodHandle spreadInvoker(MethodType type, int leadingArgCount) {
+ if (leadingArgCount < 0 || leadingArgCount > type.parameterCount())
+ throw newIllegalArgumentException("bad argument count", leadingArgCount);
+
+ MethodHandle invoker = MethodHandles.invoker(type);
+ int spreadArgCount = type.parameterCount() - leadingArgCount;
+ invoker = invoker.asSpreader(Object[].class, spreadArgCount);
+ return invoker;
+ }
+
+ /**
+ * Produces a special <em>invoker method handle</em> which can be used to
+ * invoke any method handle of the given type, as if by {@link MethodHandle#invokeExact invokeExact}.
+ * The resulting invoker will have a type which is
+ * exactly equal to the desired type, except that it will accept
+ * an additional leading argument of type {@code MethodHandle}.
+ * <p>
+ * This method is equivalent to the following code (though it may be more efficient):
+ * {@code publicLookup().findVirtual(MethodHandle.class, "invokeExact", type)}
+ *
+ * <p style="font-size:smaller;">
+ * <em>Discussion:</em>
+ * Invoker method handles can be useful when working with variable method handles
+ * of unknown types.
+ * For example, to emulate an {@code invokeExact} call to a variable method
+ * handle {@code M}, extract its type {@code T},
+ * look up the invoker method {@code X} for {@code T},
+ * and call the invoker method, as {@code X.invoke(T, A...)}.
+ * (It would not work to call {@code X.invokeExact}, since the type {@code T}
+ * is unknown.)
+ * If spreading, collecting, or other argument transformations are required,
+ * they can be applied once to the invoker {@code X} and reused on many {@code M}
+ * method handle values, as long as they are compatible with the type of {@code X}.
+ * <p style="font-size:smaller;">
+ * <em>(Note: The invoker method is not available via the Core Reflection API.
+ * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
+ * on the declared {@code invokeExact} or {@code invoke} method will raise an
+ * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
+ * <p>
+ * This method throws no reflective or security exceptions.
+ * @param type the desired target type
+ * @return a method handle suitable for invoking any method handle of the given type
+ * @throws IllegalArgumentException if the resulting method handle's type would have
+ * <a href="MethodHandle.html#maxarity">too many parameters</a>
+ */
+ static public
+ MethodHandle exactInvoker(MethodType type) {
+ return new Transformers.Invoker(type, true /* isExactInvoker */);
+ }
+
+ /**
+ * Produces a special <em>invoker method handle</em> which can be used to
+ * invoke any method handle compatible with the given type, as if by {@link MethodHandle#invoke invoke}.
+ * The resulting invoker will have a type which is
+ * exactly equal to the desired type, except that it will accept
+ * an additional leading argument of type {@code MethodHandle}.
+ * <p>
+ * Before invoking its target, if the target differs from the expected type,
+ * the invoker will apply reference casts as
+ * necessary and box, unbox, or widen primitive values, as if by {@link MethodHandle#asType asType}.
+ * Similarly, the return value will be converted as necessary.
+ * If the target is a {@linkplain MethodHandle#asVarargsCollector variable arity method handle},
+ * the required arity conversion will be made, again as if by {@link MethodHandle#asType asType}.
+ * <p>
+ * This method is equivalent to the following code (though it may be more efficient):
+ * {@code publicLookup().findVirtual(MethodHandle.class, "invoke", type)}
+ * <p style="font-size:smaller;">
+ * <em>Discussion:</em>
+ * A {@linkplain MethodType#genericMethodType general method type} is one which
+ * mentions only {@code Object} arguments and return values.
+ * An invoker for such a type is capable of calling any method handle
+ * of the same arity as the general type.
+ * <p style="font-size:smaller;">
+ * <em>(Note: The invoker method is not available via the Core Reflection API.
+ * An attempt to call {@linkplain java.lang.reflect.Method#invoke java.lang.reflect.Method.invoke}
+ * on the declared {@code invokeExact} or {@code invoke} method will raise an
+ * {@link java.lang.UnsupportedOperationException UnsupportedOperationException}.)</em>
+ * <p>
+ * This method throws no reflective or security exceptions.
+ * @param type the desired target type
+ * @return a method handle suitable for invoking any method handle convertible to the given type
+ * @throws IllegalArgumentException if the resulting method handle's type would have
+ * <a href="MethodHandle.html#maxarity">too many parameters</a>
+ */
+ static public
+ MethodHandle invoker(MethodType type) {
+ return new Transformers.Invoker(type, false /* isExactInvoker */);
+ }
+
+ // BEGIN Android-added: resolver for VarHandle accessor methods.
+ static private MethodHandle methodHandleForVarHandleAccessor(VarHandle.AccessMode accessMode,
+ MethodType type,
+ boolean isExactInvoker) {
+ Class<?> refc = VarHandle.class;
+ Method method;
+ try {
+ method = refc.getDeclaredMethod(accessMode.methodName(), Object[].class);
+ } catch (NoSuchMethodException e) {
+ throw new InternalError("No method for AccessMode " + accessMode, e);
+ }
+ MethodType methodType = type.insertParameterTypes(0, VarHandle.class);
+ int kind = isExactInvoker ? MethodHandle.INVOKE_VAR_HANDLE_EXACT
+ : MethodHandle.INVOKE_VAR_HANDLE;
+ return new MethodHandleImpl(method.getArtMethod(), kind, methodType);
+ }
+ // END Android-added: resolver for VarHandle accessor methods.
+
+ /**
+ * Produces a special <em>invoker method handle</em> which can be used to
+ * invoke a signature-polymorphic access mode method on any VarHandle whose
+ * associated access mode type is compatible with the given type.
+ * The resulting invoker will have a type which is exactly equal to the
+ * desired given type, except that it will accept an additional leading
+ * argument of type {@code VarHandle}.
+ *
+ * @param accessMode the VarHandle access mode
+ * @param type the desired target type
+ * @return a method handle suitable for invoking an access mode method of
+ * any VarHandle whose access mode type is of the given type.
+ * @since 9
+ */
+ static public
+ MethodHandle varHandleExactInvoker(VarHandle.AccessMode accessMode, MethodType type) {
+ return methodHandleForVarHandleAccessor(accessMode, type, true /* isExactInvoker */);
+ }
+
+ /**
+ * Produces a special <em>invoker method handle</em> which can be used to
+ * invoke a signature-polymorphic access mode method on any VarHandle whose
+ * associated access mode type is compatible with the given type.
+ * The resulting invoker will have a type which is exactly equal to the
+ * desired given type, except that it will accept an additional leading
+ * argument of type {@code VarHandle}.
+ * <p>
+ * Before invoking its target, if the access mode type differs from the
+ * desired given type, the invoker will apply reference casts as necessary
+ * and box, unbox, or widen primitive values, as if by
+ * {@link MethodHandle#asType asType}. Similarly, the return value will be
+ * converted as necessary.
+ * <p>
+ * This method is equivalent to the following code (though it may be more
+ * efficient): {@code publicLookup().findVirtual(VarHandle.class, accessMode.name(), type)}
+ *
+ * @param accessMode the VarHandle access mode
+ * @param type the desired target type
+ * @return a method handle suitable for invoking an access mode method of
+ * any VarHandle whose access mode type is convertible to the given
+ * type.
+ * @since 9
+ */
+ static public
+ MethodHandle varHandleInvoker(VarHandle.AccessMode accessMode, MethodType type) {
+ return methodHandleForVarHandleAccessor(accessMode, type, false /* isExactInvoker */);
+ }
+
+ // Android-changed: Basic invokers are not supported.
+ //
+ // static /*non-public*/
+ // MethodHandle basicInvoker(MethodType type) {
+ // return type.invokers().basicInvoker();
+ // }
+
+ /// method handle modification (creation from other method handles)
+
+ /**
+ * Produces a method handle which adapts the type of the
+ * given method handle to a new type by pairwise argument and return type conversion.
+ * The original type and new type must have the same number of arguments.
+ * The resulting method handle is guaranteed to report a type
+ * which is equal to the desired new type.
+ * <p>
+ * If the original type and new type are equal, returns target.
+ * <p>
+ * The same conversions are allowed as for {@link MethodHandle#asType MethodHandle.asType},
+ * and some additional conversions are also applied if those conversions fail.
+ * Given types <em>T0</em>, <em>T1</em>, one of the following conversions is applied
+ * if possible, before or instead of any conversions done by {@code asType}:
+ * <ul>
+ * <li>If <em>T0</em> and <em>T1</em> are references, and <em>T1</em> is an interface type,
+ * then the value of type <em>T0</em> is passed as a <em>T1</em> without a cast.
+ * (This treatment of interfaces follows the usage of the bytecode verifier.)
+ * <li>If <em>T0</em> is boolean and <em>T1</em> is another primitive,
+ * the boolean is converted to a byte value, 1 for true, 0 for false.
+ * (This treatment follows the usage of the bytecode verifier.)
+ * <li>If <em>T1</em> is boolean and <em>T0</em> is another primitive,
+ * <em>T0</em> is converted to byte via Java casting conversion (JLS 5.5),
+ * and the low order bit of the result is tested, as if by {@code (x & 1) != 0}.
+ * <li>If <em>T0</em> and <em>T1</em> are primitives other than boolean,
+ * then a Java casting conversion (JLS 5.5) is applied.
+ * (Specifically, <em>T0</em> will convert to <em>T1</em> by
+ * widening and/or narrowing.)
+ * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive, an unboxing
+ * conversion will be applied at runtime, possibly followed
+ * by a Java casting conversion (JLS 5.5) on the primitive value,
+ * possibly followed by a conversion from byte to boolean by testing
+ * the low-order bit.
+ * <li>If <em>T0</em> is a reference and <em>T1</em> a primitive,
+ * and if the reference is null at runtime, a zero value is introduced.
+ * </ul>
+ * @param target the method handle to invoke after arguments are retyped
+ * @param newType the expected type of the new method handle
+ * @return a method handle which delegates to the target after performing
+ * any necessary argument conversions, and arranges for any
+ * necessary return value conversions
+ * @throws NullPointerException if either argument is null
+ * @throws WrongMethodTypeException if the conversion cannot be made
+ * @see MethodHandle#asType
+ */
+ public static
+ MethodHandle explicitCastArguments(MethodHandle target, MethodType newType) {
+ explicitCastArgumentsChecks(target, newType);
+ // use the asTypeCache when possible:
+ MethodType oldType = target.type();
+ if (oldType == newType) return target;
+ if (oldType.explicitCastEquivalentToAsType(newType)) {
+ if (Transformers.Transformer.class.isAssignableFrom(target.getClass())) {
+ // The StackFrameReader and StackFrameWriter used to perform transforms on
+ // EmulatedStackFrames (in Transformers.java) do not how to perform asType()
+ // conversions, but we know here that an explicit cast transform is the same as
+ // having called asType() on the method handle.
+ return new Transformers.ExplicitCastArguments(target.asFixedArity(), newType);
+ } else {
+ // Runtime will perform asType() conversion during invocation.
+ return target.asFixedArity().asType(newType);
+ }
+ }
+ return new Transformers.ExplicitCastArguments(target, newType);
+ }
+
+ private static void explicitCastArgumentsChecks(MethodHandle target, MethodType newType) {
+ if (target.type().parameterCount() != newType.parameterCount()) {
+ throw new WrongMethodTypeException("cannot explicitly cast " + target +
+ " to " + newType);
+ }
+ }
+
+ /**
+ * Produces a method handle which adapts the calling sequence of the
+ * given method handle to a new type, by reordering the arguments.
+ * The resulting method handle is guaranteed to report a type
+ * which is equal to the desired new type.
+ * <p>
+ * The given array controls the reordering.
+ * Call {@code #I} the number of incoming parameters (the value
+ * {@code newType.parameterCount()}, and call {@code #O} the number
+ * of outgoing parameters (the value {@code target.type().parameterCount()}).
+ * Then the length of the reordering array must be {@code #O},
+ * and each element must be a non-negative number less than {@code #I}.
+ * For every {@code N} less than {@code #O}, the {@code N}-th
+ * outgoing argument will be taken from the {@code I}-th incoming
+ * argument, where {@code I} is {@code reorder[N]}.
+ * <p>
+ * No argument or return value conversions are applied.
+ * The type of each incoming argument, as determined by {@code newType},
+ * must be identical to the type of the corresponding outgoing parameter
+ * or parameters in the target method handle.
+ * The return type of {@code newType} must be identical to the return
+ * type of the original target.
+ * <p>
+ * The reordering array need not specify an actual permutation.
+ * An incoming argument will be duplicated if its index appears
+ * more than once in the array, and an incoming argument will be dropped
+ * if its index does not appear in the array.
+ * As in the case of {@link #dropArguments(MethodHandle,int,List) dropArguments},
+ * incoming arguments which are not mentioned in the reordering array
+ * are may be any type, as determined only by {@code newType}.
+ * <blockquote><pre>{@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodType intfn1 = methodType(int.class, int.class);
+MethodType intfn2 = methodType(int.class, int.class, int.class);
+MethodHandle sub = ... (int x, int y) -> (x-y) ...;
+assert(sub.type().equals(intfn2));
+MethodHandle sub1 = permuteArguments(sub, intfn2, 0, 1);
+MethodHandle rsub = permuteArguments(sub, intfn2, 1, 0);
+assert((int)rsub.invokeExact(1, 100) == 99);
+MethodHandle add = ... (int x, int y) -> (x+y) ...;
+assert(add.type().equals(intfn2));
+MethodHandle twice = permuteArguments(add, intfn1, 0, 0);
+assert(twice.type().equals(intfn1));
+assert((int)twice.invokeExact(21) == 42);
+ * }</pre></blockquote>
+ * @param target the method handle to invoke after arguments are reordered
+ * @param newType the expected type of the new method handle
+ * @param reorder an index array which controls the reordering
+ * @return a method handle which delegates to the target after it
+ * drops unused arguments and moves and/or duplicates the other arguments
+ * @throws NullPointerException if any argument is null
+ * @throws IllegalArgumentException if the index array length is not equal to
+ * the arity of the target, or if any index array element
+ * not a valid index for a parameter of {@code newType},
+ * or if two corresponding parameter types in
+ * {@code target.type()} and {@code newType} are not identical,
+ */
+ public static
+ MethodHandle permuteArguments(MethodHandle target, MethodType newType, int... reorder) {
+ reorder = reorder.clone(); // get a private copy
+ MethodType oldType = target.type();
+ permuteArgumentChecks(reorder, newType, oldType);
+
+ return new Transformers.PermuteArguments(newType, target, reorder);
+ }
+
+ // Android-changed: findFirstDupOrDrop is unused and removed.
+ // private static int findFirstDupOrDrop(int[] reorder, int newArity);
+
+ private static boolean permuteArgumentChecks(int[] reorder, MethodType newType, MethodType oldType) {
+ if (newType.returnType() != oldType.returnType())
+ throw newIllegalArgumentException("return types do not match",
+ oldType, newType);
+ if (reorder.length == oldType.parameterCount()) {
+ int limit = newType.parameterCount();
+ boolean bad = false;
+ for (int j = 0; j < reorder.length; j++) {
+ int i = reorder[j];
+ if (i < 0 || i >= limit) {
+ bad = true; break;
+ }
+ Class<?> src = newType.parameterType(i);
+ Class<?> dst = oldType.parameterType(j);
+ if (src != dst)
+ throw newIllegalArgumentException("parameter types do not match after reorder",
+ oldType, newType);
+ }
+ if (!bad) return true;
+ }
+ throw newIllegalArgumentException("bad reorder array: "+Arrays.toString(reorder));
+ }
+
+ /**
+ * Produces a method handle of the requested return type which returns the given
+ * constant value every time it is invoked.
+ * <p>
+ * Before the method handle is returned, the passed-in value is converted to the requested type.
+ * If the requested type is primitive, widening primitive conversions are attempted,
+ * else reference conversions are attempted.
+ * <p>The returned method handle is equivalent to {@code identity(type).bindTo(value)}.
+ * @param type the return type of the desired method handle
+ * @param value the value to return
+ * @return a method handle of the given return type and no arguments, which always returns the given value
+ * @throws NullPointerException if the {@code type} argument is null
+ * @throws ClassCastException if the value cannot be converted to the required return type
+ * @throws IllegalArgumentException if the given type is {@code void.class}
+ */
+ public static
+ MethodHandle constant(Class<?> type, Object value) {
+ if (type.isPrimitive()) {
+ if (type == void.class)
+ throw newIllegalArgumentException("void type");
+ Wrapper w = Wrapper.forPrimitiveType(type);
+ value = w.convert(value, type);
+ if (w.zero().equals(value))
+ return zero(w, type);
+ return insertArguments(identity(type), 0, value);
+ } else {
+ if (value == null)
+ return zero(Wrapper.OBJECT, type);
+ return identity(type).bindTo(value);
+ }
+ }
+
+ /**
+ * Produces a method handle which returns its sole argument when invoked.
+ * @param type the type of the sole parameter and return value of the desired method handle
+ * @return a unary method handle which accepts and returns the given type
+ * @throws NullPointerException if the argument is null
+ * @throws IllegalArgumentException if the given type is {@code void.class}
+ */
+ public static
+ MethodHandle identity(Class<?> type) {
+ // Android-added: explicit non-null check.
+ Objects.requireNonNull(type);
+ Wrapper btw = (type.isPrimitive() ? Wrapper.forPrimitiveType(type) : Wrapper.OBJECT);
+ int pos = btw.ordinal();
+ MethodHandle ident = IDENTITY_MHS[pos];
+ if (ident == null) {
+ ident = setCachedMethodHandle(IDENTITY_MHS, pos, makeIdentity(btw.primitiveType()));
+ }
+ if (ident.type().returnType() == type)
+ return ident;
+ // something like identity(Foo.class); do not bother to intern these
+ assert (btw == Wrapper.OBJECT);
+ return makeIdentity(type);
+ }
+
+ /**
+ * Produces a constant method handle of the requested return type which
+ * returns the default value for that type every time it is invoked.
+ * The resulting constant method handle will have no side effects.
+ * <p>The returned method handle is equivalent to {@code empty(methodType(type))}.
+ * It is also equivalent to {@code explicitCastArguments(constant(Object.class, null), methodType(type))},
+ * since {@code explicitCastArguments} converts {@code null} to default values.
+ * @param type the expected return type of the desired method handle
+ * @return a constant method handle that takes no arguments
+ * and returns the default value of the given type (or void, if the type is void)
+ * @throws NullPointerException if the argument is null
+ * @see MethodHandles#constant
+ * @see MethodHandles#empty
+ * @see MethodHandles#explicitCastArguments
+ * @since 9
+ */
+ public static MethodHandle zero(Class<?> type) {
+ Objects.requireNonNull(type);
+ return type.isPrimitive() ? zero(Wrapper.forPrimitiveType(type), type) : zero(Wrapper.OBJECT, type);
+ }
+
+ private static MethodHandle identityOrVoid(Class<?> type) {
+ return type == void.class ? zero(type) : identity(type);
+ }
+
+ /**
+ * Produces a method handle of the requested type which ignores any arguments, does nothing,
+ * and returns a suitable default depending on the return type.
+ * That is, it returns a zero primitive value, a {@code null}, or {@code void}.
+ * <p>The returned method handle is equivalent to
+ * {@code dropArguments(zero(type.returnType()), 0, type.parameterList())}.
+ *
+ * @apiNote Given a predicate and target, a useful "if-then" construct can be produced as
+ * {@code guardWithTest(pred, target, empty(target.type())}.
+ * @param type the type of the desired method handle
+ * @return a constant method handle of the given type, which returns a default value of the given return type
+ * @throws NullPointerException if the argument is null
+ * @see MethodHandles#zero
+ * @see MethodHandles#constant
+ * @since 9
+ */
+ public static MethodHandle empty(MethodType type) {
+ Objects.requireNonNull(type);
+ return dropArguments(zero(type.returnType()), 0, type.parameterList());
+ }
+
+ private static final MethodHandle[] IDENTITY_MHS = new MethodHandle[Wrapper.COUNT];
+ private static MethodHandle makeIdentity(Class<?> ptype) {
+ // Android-changed: Android implementation using identity() functions and transformers.
+ // MethodType mtype = methodType(ptype, ptype);
+ // LambdaForm lform = LambdaForm.identityForm(BasicType.basicType(ptype));
+ // return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.IDENTITY);
+ if (ptype.isPrimitive()) {
+ try {
+ final MethodType mt = methodType(ptype, ptype);
+ return Lookup.PUBLIC_LOOKUP.findStatic(MethodHandles.class, "identity", mt);
+ } catch (NoSuchMethodException | IllegalAccessException e) {
+ throw new AssertionError(e);
+ }
+ } else {
+ return new Transformers.ReferenceIdentity(ptype);
+ }
+ }
+
+ // Android-added: helper methods for identity().
+ /** @hide */ public static byte identity(byte val) { return val; }
+ /** @hide */ public static boolean identity(boolean val) { return val; }
+ /** @hide */ public static char identity(char val) { return val; }
+ /** @hide */ public static short identity(short val) { return val; }
+ /** @hide */ public static int identity(int val) { return val; }
+ /** @hide */ public static long identity(long val) { return val; }
+ /** @hide */ public static float identity(float val) { return val; }
+ /** @hide */ public static double identity(double val) { return val; }
+
+ private static MethodHandle zero(Wrapper btw, Class<?> rtype) {
+ int pos = btw.ordinal();
+ MethodHandle zero = ZERO_MHS[pos];
+ if (zero == null) {
+ zero = setCachedMethodHandle(ZERO_MHS, pos, makeZero(btw.primitiveType()));
+ }
+ if (zero.type().returnType() == rtype)
+ return zero;
+ assert(btw == Wrapper.OBJECT);
+ return makeZero(rtype);
+ }
+ private static final MethodHandle[] ZERO_MHS = new MethodHandle[Wrapper.COUNT];
+ private static MethodHandle makeZero(Class<?> rtype) {
+ // Android-changed: use Android specific implementation.
+ // MethodType mtype = methodType(rtype);
+ // LambdaForm lform = LambdaForm.zeroForm(BasicType.basicType(rtype));
+ // return MethodHandleImpl.makeIntrinsic(mtype, lform, Intrinsic.ZERO);
+ return new Transformers.ZeroValue(rtype);
+ }
+
+ private static synchronized MethodHandle setCachedMethodHandle(MethodHandle[] cache, int pos, MethodHandle value) {
+ // Simulate a CAS, to avoid racy duplication of results.
+ MethodHandle prev = cache[pos];
+ if (prev != null) return prev;
+ return cache[pos] = value;
+ }
+
+ /**
+ * Provides a target method handle with one or more <em>bound arguments</em>
+ * in advance of the method handle's invocation.
+ * The formal parameters to the target corresponding to the bound
+ * arguments are called <em>bound parameters</em>.
+ * Returns a new method handle which saves away the bound arguments.
+ * When it is invoked, it receives arguments for any non-bound parameters,
+ * binds the saved arguments to their corresponding parameters,
+ * and calls the original target.
+ * <p>
+ * The type of the new method handle will drop the types for the bound
+ * parameters from the original target type, since the new method handle
+ * will no longer require those arguments to be supplied by its callers.
+ * <p>
+ * Each given argument object must match the corresponding bound parameter type.
+ * If a bound parameter type is a primitive, the argument object
+ * must be a wrapper, and will be unboxed to produce the primitive value.
+ * <p>
+ * The {@code pos} argument selects which parameters are to be bound.
+ * It may range between zero and <i>N-L</i> (inclusively),
+ * where <i>N</i> is the arity of the target method handle
+ * and <i>L</i> is the length of the values array.
+ * @param target the method handle to invoke after the argument is inserted
+ * @param pos where to insert the argument (zero for the first)
+ * @param values the series of arguments to insert
+ * @return a method handle which inserts an additional argument,
+ * before calling the original method handle
+ * @throws NullPointerException if the target or the {@code values} array is null
+ * @see MethodHandle#bindTo
+ */
+ public static
+ MethodHandle insertArguments(MethodHandle target, int pos, Object... values) {
+ int insCount = values.length;
+ Class<?>[] ptypes = insertArgumentsChecks(target, insCount, pos);
+ if (insCount == 0) {
+ return target;
+ }
+
+ // Throw ClassCastExceptions early if we can't cast any of the provided values
+ // to the required type.
+ for (int i = 0; i < insCount; i++) {
+ final Class<?> ptype = ptypes[pos + i];
+ if (!ptype.isPrimitive()) {
+ ptypes[pos + i].cast(values[i]);
+ } else {
+ // Will throw a ClassCastException if something terrible happens.
+ values[i] = Wrapper.forPrimitiveType(ptype).convert(values[i], ptype);
+ }
+ }
+
+ return new Transformers.InsertArguments(target, pos, values);
+ }
+
+ // Android-changed: insertArgumentPrimitive is unused.
+ //
+ // private static BoundMethodHandle insertArgumentPrimitive(BoundMethodHandle result, int pos,
+ // Class<?> ptype, Object value) {
+ // Wrapper w = Wrapper.forPrimitiveType(ptype);
+ // // perform unboxing and/or primitive conversion
+ // value = w.convert(value, ptype);
+ // switch (w) {
+ // case INT: return result.bindArgumentI(pos, (int)value);
+ // case LONG: return result.bindArgumentJ(pos, (long)value);
+ // case FLOAT: return result.bindArgumentF(pos, (float)value);
+ // case DOUBLE: return result.bindArgumentD(pos, (double)value);
+ // default: return result.bindArgumentI(pos, ValueConversions.widenSubword(value));
+ // }
+ // }
+
+ private static Class<?>[] insertArgumentsChecks(MethodHandle target, int insCount, int pos) throws RuntimeException {
+ MethodType oldType = target.type();
+ int outargs = oldType.parameterCount();
+ int inargs = outargs - insCount;
+ if (inargs < 0)
+ throw newIllegalArgumentException("too many values to insert");
+ if (pos < 0 || pos > inargs)
+ throw newIllegalArgumentException("no argument type to append");
+ return oldType.ptypes();
+ }
+
+ // Android-changed: inclusive language preference for 'placeholder'.
+ /**
+ * Produces a method handle which will discard some placeholder arguments
+ * before calling some other specified <i>target</i> method handle.
+ * The type of the new method handle will be the same as the target's type,
+ * except it will also include the placeholder argument types,
+ * at some given position.
+ * <p>
+ * The {@code pos} argument may range between zero and <i>N</i>,
+ * where <i>N</i> is the arity of the target.
+ * If {@code pos} is zero, the placeholder arguments will precede
+ * the target's real arguments; if {@code pos} is <i>N</i>
+ * they will come after.
+ * <p>
+ * <b>Example:</b>
+ * <blockquote><pre>{@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+assertEquals("xy", (String) cat.invokeExact("x", "y"));
+MethodType bigType = cat.type().insertParameterTypes(0, int.class, String.class);
+MethodHandle d0 = dropArguments(cat, 0, bigType.parameterList().subList(0,2));
+assertEquals(bigType, d0.type());
+assertEquals("yz", (String) d0.invokeExact(123, "x", "y", "z"));
+ * }</pre></blockquote>
+ * <p>
+ * This method is also equivalent to the following code:
+ * <blockquote><pre>
+ * {@link #dropArguments(MethodHandle,int,Class...) dropArguments}{@code (target, pos, valueTypes.toArray(new Class[0]))}
+ * </pre></blockquote>
+ * @param target the method handle to invoke after the arguments are dropped
+ * @param valueTypes the type(s) of the argument(s) to drop
+ * @param pos position of first argument to drop (zero for the leftmost)
+ * @return a method handle which drops arguments of the given types,
+ * before calling the original method handle
+ * @throws NullPointerException if the target is null,
+ * or if the {@code valueTypes} list or any of its elements is null
+ * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
+ * or if {@code pos} is negative or greater than the arity of the target,
+ * or if the new method handle's type would have too many parameters
+ */
+ public static
+ MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
+ return dropArguments0(target, pos, copyTypes(valueTypes.toArray()));
+ }
+
+ private static List<Class<?>> copyTypes(Object[] array) {
+ return Arrays.asList(Arrays.copyOf(array, array.length, Class[].class));
+ }
+
+ private static
+ MethodHandle dropArguments0(MethodHandle target, int pos, List<Class<?>> valueTypes) {
+ MethodType oldType = target.type(); // get NPE
+ int dropped = dropArgumentChecks(oldType, pos, valueTypes);
+ MethodType newType = oldType.insertParameterTypes(pos, valueTypes);
+ if (dropped == 0) return target;
+ // Android-changed: transformer implementation.
+ // BoundMethodHandle result = target.rebind();
+ // LambdaForm lform = result.form;
+ // int insertFormArg = 1 + pos;
+ // for (Class<?> ptype : valueTypes) {
+ // lform = lform.editor().addArgumentForm(insertFormArg++, BasicType.basicType(ptype));
+ // }
+ // result = result.copyWith(newType, lform);
+ // return result;
+ return new Transformers.DropArguments(newType, target, pos, dropped);
+ }
+
+ private static int dropArgumentChecks(MethodType oldType, int pos, List<Class<?>> valueTypes) {
+ int dropped = valueTypes.size();
+ MethodType.checkSlotCount(dropped);
+ int outargs = oldType.parameterCount();
+ int inargs = outargs + dropped;
+ if (pos < 0 || pos > outargs)
+ throw newIllegalArgumentException("no argument type to remove"
+ + Arrays.asList(oldType, pos, valueTypes, inargs, outargs)
+ );
+ return dropped;
+ }
+
+ // Android-changed: inclusive language preference for 'placeholder'.
+ /**
+ * Produces a method handle which will discard some placeholder arguments
+ * before calling some other specified <i>target</i> method handle.
+ * The type of the new method handle will be the same as the target's type,
+ * except it will also include the placeholder argument types,
+ * at some given position.
+ * <p>
+ * The {@code pos} argument may range between zero and <i>N</i>,
+ * where <i>N</i> is the arity of the target.
+ * If {@code pos} is zero, the placeholder arguments will precede
+ * the target's real arguments; if {@code pos} is <i>N</i>
+ * they will come after.
+ * @apiNote
+ * <blockquote><pre>{@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+assertEquals("xy", (String) cat.invokeExact("x", "y"));
+MethodHandle d0 = dropArguments(cat, 0, String.class);
+assertEquals("yz", (String) d0.invokeExact("x", "y", "z"));
+MethodHandle d1 = dropArguments(cat, 1, String.class);
+assertEquals("xz", (String) d1.invokeExact("x", "y", "z"));
+MethodHandle d2 = dropArguments(cat, 2, String.class);
+assertEquals("xy", (String) d2.invokeExact("x", "y", "z"));
+MethodHandle d12 = dropArguments(cat, 1, int.class, boolean.class);
+assertEquals("xz", (String) d12.invokeExact("x", 12, true, "z"));
+ * }</pre></blockquote>
+ * <p>
+ * This method is also equivalent to the following code:
+ * <blockquote><pre>
+ * {@link #dropArguments(MethodHandle,int,List) dropArguments}{@code (target, pos, Arrays.asList(valueTypes))}
+ * </pre></blockquote>
+ * @param target the method handle to invoke after the arguments are dropped
+ * @param valueTypes the type(s) of the argument(s) to drop
+ * @param pos position of first argument to drop (zero for the leftmost)
+ * @return a method handle which drops arguments of the given types,
+ * before calling the original method handle
+ * @throws NullPointerException if the target is null,
+ * or if the {@code valueTypes} array or any of its elements is null
+ * @throws IllegalArgumentException if any element of {@code valueTypes} is {@code void.class},
+ * or if {@code pos} is negative or greater than the arity of the target,
+ * or if the new method handle's type would have
+ * <a href="MethodHandle.html#maxarity">too many parameters</a>
+ */
+ public static
+ MethodHandle dropArguments(MethodHandle target, int pos, Class<?>... valueTypes) {
+ return dropArguments0(target, pos, copyTypes(valueTypes));
+ }
+
+ // private version which allows caller some freedom with error handling
+ private static MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos,
+ boolean nullOnFailure) {
+ newTypes = copyTypes(newTypes.toArray());
+ List<Class<?>> oldTypes = target.type().parameterList();
+ int match = oldTypes.size();
+ if (skip != 0) {
+ if (skip < 0 || skip > match) {
+ throw newIllegalArgumentException("illegal skip", skip, target);
+ }
+ oldTypes = oldTypes.subList(skip, match);
+ match -= skip;
+ }
+ List<Class<?>> addTypes = newTypes;
+ int add = addTypes.size();
+ if (pos != 0) {
+ if (pos < 0 || pos > add) {
+ throw newIllegalArgumentException("illegal pos", pos, newTypes);
+ }
+ addTypes = addTypes.subList(pos, add);
+ add -= pos;
+ assert(addTypes.size() == add);
+ }
+ // Do not add types which already match the existing arguments.
+ if (match > add || !oldTypes.equals(addTypes.subList(0, match))) {
+ if (nullOnFailure) {
+ return null;
+ }
+ throw newIllegalArgumentException("argument lists do not match", oldTypes, newTypes);
+ }
+ addTypes = addTypes.subList(match, add);
+ add -= match;
+ assert(addTypes.size() == add);
+ // newTypes: ( P*[pos], M*[match], A*[add] )
+ // target: ( S*[skip], M*[match] )
+ MethodHandle adapter = target;
+ if (add > 0) {
+ adapter = dropArguments0(adapter, skip+ match, addTypes);
+ }
+ // adapter: (S*[skip], M*[match], A*[add] )
+ if (pos > 0) {
+ adapter = dropArguments0(adapter, skip, newTypes.subList(0, pos));
+ }
+ // adapter: (S*[skip], P*[pos], M*[match], A*[add] )
+ return adapter;
+ }
+
+ // Android-changed: inclusive language preference for 'placeholder'.
+ /**
+ * Adapts a target method handle to match the given parameter type list. If necessary, adds placeholder arguments. Some
+ * leading parameters can be skipped before matching begins. The remaining types in the {@code target}'s parameter
+ * type list must be a sub-list of the {@code newTypes} type list at the starting position {@code pos}. The
+ * resulting handle will have the target handle's parameter type list, with any non-matching parameter types (before
+ * or after the matching sub-list) inserted in corresponding positions of the target's original parameters, as if by
+ * {@link #dropArguments(MethodHandle, int, Class[])}.
+ * <p>
+ * The resulting handle will have the same return type as the target handle.
+ * <p>
+ * In more formal terms, assume these two type lists:<ul>
+ * <li>The target handle has the parameter type list {@code S..., M...}, with as many types in {@code S} as
+ * indicated by {@code skip}. The {@code M} types are those that are supposed to match part of the given type list,
+ * {@code newTypes}.
+ * <li>The {@code newTypes} list contains types {@code P..., M..., A...}, with as many types in {@code P} as
+ * indicated by {@code pos}. The {@code M} types are precisely those that the {@code M} types in the target handle's
+ * parameter type list are supposed to match. The types in {@code A} are additional types found after the matching
+ * sub-list.
+ * </ul>
+ * Given these assumptions, the result of an invocation of {@code dropArgumentsToMatch} will have the parameter type
+ * list {@code S..., P..., M..., A...}, with the {@code P} and {@code A} types inserted as if by
+ * {@link #dropArguments(MethodHandle, int, Class[])}.
+ *
+ * @apiNote
+ * Two method handles whose argument lists are "effectively identical" (i.e., identical in a common prefix) may be
+ * mutually converted to a common type by two calls to {@code dropArgumentsToMatch}, as follows:
+ * <blockquote><pre>{@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+...
+MethodHandle h0 = constant(boolean.class, true);
+MethodHandle h1 = lookup().findVirtual(String.class, "concat", methodType(String.class, String.class));
+MethodType bigType = h1.type().insertParameterTypes(1, String.class, int.class);
+MethodHandle h2 = dropArguments(h1, 0, bigType.parameterList());
+if (h1.type().parameterCount() < h2.type().parameterCount())
+ h1 = dropArgumentsToMatch(h1, 0, h2.type().parameterList(), 0); // lengthen h1
+else
+ h2 = dropArgumentsToMatch(h2, 0, h1.type().parameterList(), 0); // lengthen h2
+MethodHandle h3 = guardWithTest(h0, h1, h2);
+assertEquals("xy", h3.invoke("x", "y", 1, "a", "b", "c"));
+ * }</pre></blockquote>
+ * @param target the method handle to adapt
+ * @param skip number of targets parameters to disregard (they will be unchanged)
+ * @param newTypes the list of types to match {@code target}'s parameter type list to
+ * @param pos place in {@code newTypes} where the non-skipped target parameters must occur
+ * @return a possibly adapted method handle
+ * @throws NullPointerException if either argument is null
+ * @throws IllegalArgumentException if any element of {@code newTypes} is {@code void.class},
+ * or if {@code skip} is negative or greater than the arity of the target,
+ * or if {@code pos} is negative or greater than the newTypes list size,
+ * or if {@code newTypes} does not contain the {@code target}'s non-skipped parameter types at position
+ * {@code pos}.
+ * @since 9
+ */
+ public static
+ MethodHandle dropArgumentsToMatch(MethodHandle target, int skip, List<Class<?>> newTypes, int pos) {
+ Objects.requireNonNull(target);
+ Objects.requireNonNull(newTypes);
+ return dropArgumentsToMatch(target, skip, newTypes, pos, false);
+ }
+
+ /**
+ * Drop the return value of the target handle (if any).
+ * The returned method handle will have a {@code void} return type.
+ *
+ * @param target the method handle to adapt
+ * @return a possibly adapted method handle
+ * @throws NullPointerException if {@code target} is null
+ * @since 16
+ */
+ public static MethodHandle dropReturn(MethodHandle target) {
+ Objects.requireNonNull(target);
+ MethodType oldType = target.type();
+ Class<?> oldReturnType = oldType.returnType();
+ if (oldReturnType == void.class)
+ return target;
+
+ MethodType newType = oldType.changeReturnType(void.class);
+ // Android-changed: no support for BoundMethodHandle or LambdaForm.
+ // BoundMethodHandle result = target.rebind();
+ // LambdaForm lform = result.editor().filterReturnForm(V_TYPE, true);
+ // result = result.copyWith(newType, lform);
+ // return result;
+ return target.asType(newType);
+ }
+
+ /**
+ * Adapts a target method handle by pre-processing
+ * one or more of its arguments, each with its own unary filter function,
+ * and then calling the target with each pre-processed argument
+ * replaced by the result of its corresponding filter function.
+ * <p>
+ * The pre-processing is performed by one or more method handles,
+ * specified in the elements of the {@code filters} array.
+ * The first element of the filter array corresponds to the {@code pos}
+ * argument of the target, and so on in sequence.
+ * The filter functions are invoked in left to right order.
+ * <p>
+ * Null arguments in the array are treated as identity functions,
+ * and the corresponding arguments left unchanged.
+ * (If there are no non-null elements in the array, the original target is returned.)
+ * Each filter is applied to the corresponding argument of the adapter.
+ * <p>
+ * If a filter {@code F} applies to the {@code N}th argument of
+ * the target, then {@code F} must be a method handle which
+ * takes exactly one argument. The type of {@code F}'s sole argument
+ * replaces the corresponding argument type of the target
+ * in the resulting adapted method handle.
+ * The return type of {@code F} must be identical to the corresponding
+ * parameter type of the target.
+ * <p>
+ * It is an error if there are elements of {@code filters}
+ * (null or not)
+ * which do not correspond to argument positions in the target.
+ * <p><b>Example:</b>
+ * <blockquote><pre>{@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+MethodHandle upcase = lookup().findVirtual(String.class,
+ "toUpperCase", methodType(String.class));
+assertEquals("xy", (String) cat.invokeExact("x", "y"));
+MethodHandle f0 = filterArguments(cat, 0, upcase);
+assertEquals("Xy", (String) f0.invokeExact("x", "y")); // Xy
+MethodHandle f1 = filterArguments(cat, 1, upcase);
+assertEquals("xY", (String) f1.invokeExact("x", "y")); // xY
+MethodHandle f2 = filterArguments(cat, 0, upcase, upcase);
+assertEquals("XY", (String) f2.invokeExact("x", "y")); // XY
+ * }</pre></blockquote>
+ * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
+ * denotes the return type of both the {@code target} and resulting adapter.
+ * {@code P}/{@code p} and {@code B}/{@code b} represent the types and values
+ * of the parameters and arguments that precede and follow the filter position
+ * {@code pos}, respectively. {@code A[i]}/{@code a[i]} stand for the types and
+ * values of the filtered parameters and arguments; they also represent the
+ * return types of the {@code filter[i]} handles. The latter accept arguments
+ * {@code v[i]} of type {@code V[i]}, which also appear in the signature of
+ * the resulting adapter.
+ * <blockquote><pre>{@code
+ * T target(P... p, A[i]... a[i], B... b);
+ * A[i] filter[i](V[i]);
+ * T adapter(P... p, V[i]... v[i], B... b) {
+ * return target(p..., filter[i](v[i])..., b...);
+ * }
+ * }</pre></blockquote>
+ * <p>
+ * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
+ * variable-arity method handle}, even if the original target method handle was.
+ *
+ * @param target the method handle to invoke after arguments are filtered
+ * @param pos the position of the first argument to filter
+ * @param filters method handles to call initially on filtered arguments
+ * @return method handle which incorporates the specified argument filtering logic
+ * @throws NullPointerException if the target is null
+ * or if the {@code filters} array is null
+ * @throws IllegalArgumentException if a non-null element of {@code filters}
+ * does not match a corresponding argument type of target as described above,
+ * or if the {@code pos+filters.length} is greater than {@code target.type().parameterCount()},
+ * or if the resulting method handle's type would have
+ * <a href="MethodHandle.html#maxarity">too many parameters</a>
+ */
+ public static
+ MethodHandle filterArguments(MethodHandle target, int pos, MethodHandle... filters) {
+ filterArgumentsCheckArity(target, pos, filters);
+ MethodHandle adapter = target;
+ // Android-changed: transformer implementation.
+ // process filters in reverse order so that the invocation of
+ // the resulting adapter will invoke the filters in left-to-right order
+ // for (int i = filters.length - 1; i >= 0; --i) {
+ // MethodHandle filter = filters[i];
+ // if (filter == null) continue; // ignore null elements of filters
+ // adapter = filterArgument(adapter, pos + i, filter);
+ // }
+ // return adapter;
+ boolean hasNonNullFilter = false;
+ for (int i = 0; i < filters.length; ++i) {
+ MethodHandle filter = filters[i];
+ if (filter != null) {
+ hasNonNullFilter = true;
+ filterArgumentChecks(target, i + pos, filter);
+ }
+ }
+ if (!hasNonNullFilter) {
+ return target;
+ }
+ return new Transformers.FilterArguments(target, pos, filters);
+ }
+
+ /*non-public*/ static
+ MethodHandle filterArgument(MethodHandle target, int pos, MethodHandle filter) {
+ filterArgumentChecks(target, pos, filter);
+ // Android-changed: use Transformer implementation.
+ // MethodType targetType = target.type();
+ // MethodType filterType = filter.type();
+ // BoundMethodHandle result = target.rebind();
+ // Class<?> newParamType = filterType.parameterType(0);
+ // LambdaForm lform = result.editor().filterArgumentForm(1 + pos, BasicType.basicType(newParamType));
+ // MethodType newType = targetType.changeParameterType(pos, newParamType);
+ // result = result.copyWithExtendL(newType, lform, filter);
+ // return result;
+ return new Transformers.FilterArguments(target, pos, filter);
+ }
+
+ private static void filterArgumentsCheckArity(MethodHandle target, int pos, MethodHandle[] filters) {
+ MethodType targetType = target.type();
+ int maxPos = targetType.parameterCount();
+ if (pos + filters.length > maxPos)
+ throw newIllegalArgumentException("too many filters");
+ }
+
+ private static void filterArgumentChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
+ MethodType targetType = target.type();
+ MethodType filterType = filter.type();
+ if (filterType.parameterCount() != 1
+ || filterType.returnType() != targetType.parameterType(pos))
+ throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
+ }
+
+ /**
+ * Adapts a target method handle by pre-processing
+ * a sub-sequence of its arguments with a filter (another method handle).
+ * The pre-processed arguments are replaced by the result (if any) of the
+ * filter function.
+ * The target is then called on the modified (usually shortened) argument list.
+ * <p>
+ * If the filter returns a value, the target must accept that value as
+ * its argument in position {@code pos}, preceded and/or followed by
+ * any arguments not passed to the filter.
+ * If the filter returns void, the target must accept all arguments
+ * not passed to the filter.
+ * No arguments are reordered, and a result returned from the filter
+ * replaces (in order) the whole subsequence of arguments originally
+ * passed to the adapter.
+ * <p>
+ * The argument types (if any) of the filter
+ * replace zero or one argument types of the target, at position {@code pos},
+ * in the resulting adapted method handle.
+ * The return type of the filter (if any) must be identical to the
+ * argument type of the target at position {@code pos}, and that target argument
+ * is supplied by the return value of the filter.
+ * <p>
+ * In all cases, {@code pos} must be greater than or equal to zero, and
+ * {@code pos} must also be less than or equal to the target's arity.
+ * <p><b>Example:</b>
+ * <blockquote><pre>{@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle deepToString = publicLookup()
+ .findStatic(Arrays.class, "deepToString", methodType(String.class, Object[].class));
+
+MethodHandle ts1 = deepToString.asCollector(String[].class, 1);
+assertEquals("[strange]", (String) ts1.invokeExact("strange"));
+
+MethodHandle ts2 = deepToString.asCollector(String[].class, 2);
+assertEquals("[up, down]", (String) ts2.invokeExact("up", "down"));
+
+MethodHandle ts3 = deepToString.asCollector(String[].class, 3);
+MethodHandle ts3_ts2 = collectArguments(ts3, 1, ts2);
+assertEquals("[top, [up, down], strange]",
+ (String) ts3_ts2.invokeExact("top", "up", "down", "strange"));
+
+MethodHandle ts3_ts2_ts1 = collectArguments(ts3_ts2, 3, ts1);
+assertEquals("[top, [up, down], [strange]]",
+ (String) ts3_ts2_ts1.invokeExact("top", "up", "down", "strange"));
+
+MethodHandle ts3_ts2_ts3 = collectArguments(ts3_ts2, 1, ts3);
+assertEquals("[top, [[up, down, strange], charm], bottom]",
+ (String) ts3_ts2_ts3.invokeExact("top", "up", "down", "strange", "charm", "bottom"));
+ * }</pre></blockquote>
+ * <p> Here is pseudocode for the resulting adapter:
+ * <blockquote><pre>{@code
+ * T target(A...,V,C...);
+ * V filter(B...);
+ * T adapter(A... a,B... b,C... c) {
+ * V v = filter(b...);
+ * return target(a...,v,c...);
+ * }
+ * // and if the filter has no arguments:
+ * T target2(A...,V,C...);
+ * V filter2();
+ * T adapter2(A... a,C... c) {
+ * V v = filter2();
+ * return target2(a...,v,c...);
+ * }
+ * // and if the filter has a void return:
+ * T target3(A...,C...);
+ * void filter3(B...);
+ * void adapter3(A... a,B... b,C... c) {
+ * filter3(b...);
+ * return target3(a...,c...);
+ * }
+ * }</pre></blockquote>
+ * <p>
+ * A collection adapter {@code collectArguments(mh, 0, coll)} is equivalent to
+ * one which first "folds" the affected arguments, and then drops them, in separate
+ * steps as follows:
+ * <blockquote><pre>{@code
+ * mh = MethodHandles.dropArguments(mh, 1, coll.type().parameterList()); //step 2
+ * mh = MethodHandles.foldArguments(mh, coll); //step 1
+ * }</pre></blockquote>
+ * If the target method handle consumes no arguments besides than the result
+ * (if any) of the filter {@code coll}, then {@code collectArguments(mh, 0, coll)}
+ * is equivalent to {@code filterReturnValue(coll, mh)}.
+ * If the filter method handle {@code coll} consumes one argument and produces
+ * a non-void result, then {@code collectArguments(mh, N, coll)}
+ * is equivalent to {@code filterArguments(mh, N, coll)}.
+ * Other equivalences are possible but would require argument permutation.
+ *
+ * @param target the method handle to invoke after filtering the subsequence of arguments
+ * @param pos the position of the first adapter argument to pass to the filter,
+ * and/or the target argument which receives the result of the filter
+ * @param filter method handle to call on the subsequence of arguments
+ * @return method handle which incorporates the specified argument subsequence filtering logic
+ * @throws NullPointerException if either argument is null
+ * @throws IllegalArgumentException if the return type of {@code filter}
+ * is non-void and is not the same as the {@code pos} argument of the target,
+ * or if {@code pos} is not between 0 and the target's arity, inclusive,
+ * or if the resulting method handle's type would have
+ * <a href="MethodHandle.html#maxarity">too many parameters</a>
+ * @see MethodHandles#foldArguments
+ * @see MethodHandles#filterArguments
+ * @see MethodHandles#filterReturnValue
+ */
+ public static
+ MethodHandle collectArguments(MethodHandle target, int pos, MethodHandle filter) {
+ MethodType newType = collectArgumentsChecks(target, pos, filter);
+ return new Transformers.CollectArguments(target, filter, pos, newType);
+ }
+
+ private static MethodType collectArgumentsChecks(MethodHandle target, int pos, MethodHandle filter) throws RuntimeException {
+ MethodType targetType = target.type();
+ MethodType filterType = filter.type();
+ Class<?> rtype = filterType.returnType();
+ List<Class<?>> filterArgs = filterType.parameterList();
+ if (rtype == void.class) {
+ return targetType.insertParameterTypes(pos, filterArgs);
+ }
+ if (rtype != targetType.parameterType(pos)) {
+ throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
+ }
+ return targetType.dropParameterTypes(pos, pos+1).insertParameterTypes(pos, filterArgs);
+ }
+
+ /**
+ * Adapts a target method handle by post-processing
+ * its return value (if any) with a filter (another method handle).
+ * The result of the filter is returned from the adapter.
+ * <p>
+ * If the target returns a value, the filter must accept that value as
+ * its only argument.
+ * If the target returns void, the filter must accept no arguments.
+ * <p>
+ * The return type of the filter
+ * replaces the return type of the target
+ * in the resulting adapted method handle.
+ * The argument type of the filter (if any) must be identical to the
+ * return type of the target.
+ * <p><b>Example:</b>
+ * <blockquote><pre>{@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+MethodHandle length = lookup().findVirtual(String.class,
+ "length", methodType(int.class));
+System.out.println((String) cat.invokeExact("x", "y")); // xy
+MethodHandle f0 = filterReturnValue(cat, length);
+System.out.println((int) f0.invokeExact("x", "y")); // 2
+ * }</pre></blockquote>
+ * <p>Here is pseudocode for the resulting adapter. In the code,
+ * {@code T}/{@code t} represent the result type and value of the
+ * {@code target}; {@code V}, the result type of the {@code filter}; and
+ * {@code A}/{@code a}, the types and values of the parameters and arguments
+ * of the {@code target} as well as the resulting adapter.
+ * <blockquote><pre>{@code
+ * T target(A...);
+ * V filter(T);
+ * V adapter(A... a) {
+ * T t = target(a...);
+ * return filter(t);
+ * }
+ * // and if the target has a void return:
+ * void target2(A...);
+ * V filter2();
+ * V adapter2(A... a) {
+ * target2(a...);
+ * return filter2();
+ * }
+ * // and if the filter has a void return:
+ * T target3(A...);
+ * void filter3(V);
+ * void adapter3(A... a) {
+ * T t = target3(a...);
+ * filter3(t);
+ * }
+ * }</pre></blockquote>
+ * <p>
+ * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
+ * variable-arity method handle}, even if the original target method handle was.
+ * @param target the method handle to invoke before filtering the return value
+ * @param filter method handle to call on the return value
+ * @return method handle which incorporates the specified return value filtering logic
+ * @throws NullPointerException if either argument is null
+ * @throws IllegalArgumentException if the argument list of {@code filter}
+ * does not match the return type of target as described above
+ */
+ public static
+ MethodHandle filterReturnValue(MethodHandle target, MethodHandle filter) {
+ MethodType targetType = target.type();
+ MethodType filterType = filter.type();
+ filterReturnValueChecks(targetType, filterType);
+ // Android-changed: use a transformer.
+ // BoundMethodHandle result = target.rebind();
+ // BasicType rtype = BasicType.basicType(filterType.returnType());
+ // LambdaForm lform = result.editor().filterReturnForm(rtype, false);
+ // MethodType newType = targetType.changeReturnType(filterType.returnType());
+ // result = result.copyWithExtendL(newType, lform, filter);
+ // return result;
+ return new Transformers.FilterReturnValue(target, filter);
+ }
+
+ private static void filterReturnValueChecks(MethodType targetType, MethodType filterType) throws RuntimeException {
+ Class<?> rtype = targetType.returnType();
+ int filterValues = filterType.parameterCount();
+ if (filterValues == 0
+ ? (rtype != void.class)
+ : (rtype != filterType.parameterType(0) || filterValues != 1))
+ throw newIllegalArgumentException("target and filter types do not match", targetType, filterType);
+ }
+
+ /**
+ * Adapts a target method handle by pre-processing
+ * some of its arguments, and then calling the target with
+ * the result of the pre-processing, inserted into the original
+ * sequence of arguments.
+ * <p>
+ * The pre-processing is performed by {@code combiner}, a second method handle.
+ * Of the arguments passed to the adapter, the first {@code N} arguments
+ * are copied to the combiner, which is then called.
+ * (Here, {@code N} is defined as the parameter count of the combiner.)
+ * After this, control passes to the target, with any result
+ * from the combiner inserted before the original {@code N} incoming
+ * arguments.
+ * <p>
+ * If the combiner returns a value, the first parameter type of the target
+ * must be identical with the return type of the combiner, and the next
+ * {@code N} parameter types of the target must exactly match the parameters
+ * of the combiner.
+ * <p>
+ * If the combiner has a void return, no result will be inserted,
+ * and the first {@code N} parameter types of the target
+ * must exactly match the parameters of the combiner.
+ * <p>
+ * The resulting adapter is the same type as the target, except that the
+ * first parameter type is dropped,
+ * if it corresponds to the result of the combiner.
+ * <p>
+ * (Note that {@link #dropArguments(MethodHandle,int,List) dropArguments} can be used to remove any arguments
+ * that either the combiner or the target does not wish to receive.
+ * If some of the incoming arguments are destined only for the combiner,
+ * consider using {@link MethodHandle#asCollector asCollector} instead, since those
+ * arguments will not need to be live on the stack on entry to the
+ * target.)
+ * <p><b>Example:</b>
+ * <blockquote><pre>{@code
+import static java.lang.invoke.MethodHandles.*;
+import static java.lang.invoke.MethodType.*;
+...
+MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
+ "println", methodType(void.class, String.class))
+ .bindTo(System.out);
+MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
+MethodHandle catTrace = foldArguments(cat, trace);
+// also prints "boo":
+assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
+ * }</pre></blockquote>
+ * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
+ * represents the result type of the {@code target} and resulting adapter.
+ * {@code V}/{@code v} represent the type and value of the parameter and argument
+ * of {@code target} that precedes the folding position; {@code V} also is
+ * the result type of the {@code combiner}. {@code A}/{@code a} denote the
+ * types and values of the {@code N} parameters and arguments at the folding
+ * position. {@code B}/{@code b} represent the types and values of the
+ * {@code target} parameters and arguments that follow the folded parameters
+ * and arguments.
+ * <blockquote><pre>{@code
+ * // there are N arguments in A...
+ * T target(V, A[N]..., B...);
+ * V combiner(A...);
+ * T adapter(A... a, B... b) {
+ * V v = combiner(a...);
+ * return target(v, a..., b...);
+ * }
+ * // and if the combiner has a void return:
+ * T target2(A[N]..., B...);
+ * void combiner2(A...);
+ * T adapter2(A... a, B... b) {
+ * combiner2(a...);
+ * return target2(a..., b...);
+ * }
+ * }</pre></blockquote>
+ * <p>
+ * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
+ * variable-arity method handle}, even if the original target method handle was.
+ * @param target the method handle to invoke after arguments are combined
+ * @param combiner method handle to call initially on the incoming arguments
+ * @return method handle which incorporates the specified argument folding logic
+ * @throws NullPointerException if either argument is null
+ * @throws IllegalArgumentException if {@code combiner}'s return type
+ * is non-void and not the same as the first argument type of
+ * the target, or if the initial {@code N} argument types
+ * of the target
+ * (skipping one matching the {@code combiner}'s return type)
+ * are not identical with the argument types of {@code combiner}
+ */
+ public static
+ MethodHandle foldArguments(MethodHandle target, MethodHandle combiner) {
+ return foldArguments(target, 0, combiner);
+ }
+
+ /**
+ * Adapts a target method handle by pre-processing some of its arguments, starting at a given position, and then
+ * calling the target with the result of the pre-processing, inserted into the original sequence of arguments just
+ * before the folded arguments.
+ * <p>
+ * This method is closely related to {@link #foldArguments(MethodHandle, MethodHandle)}, but allows to control the
+ * position in the parameter list at which folding takes place. The argument controlling this, {@code pos}, is a
+ * zero-based index. The aforementioned method {@link #foldArguments(MethodHandle, MethodHandle)} assumes position
+ * 0.
+ *
+ * @apiNote Example:
+ * <blockquote><pre>{@code
+ import static java.lang.invoke.MethodHandles.*;
+ import static java.lang.invoke.MethodType.*;
+ ...
+ MethodHandle trace = publicLookup().findVirtual(java.io.PrintStream.class,
+ "println", methodType(void.class, String.class))
+ .bindTo(System.out);
+ MethodHandle cat = lookup().findVirtual(String.class,
+ "concat", methodType(String.class, String.class));
+ assertEquals("boojum", (String) cat.invokeExact("boo", "jum"));
+ MethodHandle catTrace = foldArguments(cat, 1, trace);
+ // also prints "jum":
+ assertEquals("boojum", (String) catTrace.invokeExact("boo", "jum"));
+ * }</pre></blockquote>
+ * <p>Here is pseudocode for the resulting adapter. In the code, {@code T}
+ * represents the result type of the {@code target} and resulting adapter.
+ * {@code V}/{@code v} represent the type and value of the parameter and argument
+ * of {@code target} that precedes the folding position; {@code V} also is
+ * the result type of the {@code combiner}. {@code A}/{@code a} denote the
+ * types and values of the {@code N} parameters and arguments at the folding
+ * position. {@code Z}/{@code z} and {@code B}/{@code b} represent the types
+ * and values of the {@code target} parameters and arguments that precede and
+ * follow the folded parameters and arguments starting at {@code pos},
+ * respectively.
+ * <blockquote><pre>{@code
+ * // there are N arguments in A...
+ * T target(Z..., V, A[N]..., B...);
+ * V combiner(A...);
+ * T adapter(Z... z, A... a, B... b) {
+ * V v = combiner(a...);
+ * return target(z..., v, a..., b...);
+ * }
+ * // and if the combiner has a void return:
+ * T target2(Z..., A[N]..., B...);
+ * void combiner2(A...);
+ * T adapter2(Z... z, A... a, B... b) {
+ * combiner2(a...);
+ * return target2(z..., a..., b...);
+ * }
+ * }</pre></blockquote>
+ * <p>
+ * <em>Note:</em> The resulting adapter is never a {@linkplain MethodHandle#asVarargsCollector
+ * variable-arity method handle}, even if the original target method handle was.
+ *
+ * @param target the method handle to invoke after arguments are combined
+ * @param pos the position at which to start folding and at which to insert the folding result; if this is {@code
+ * 0}, the effect is the same as for {@link #foldArguments(MethodHandle, MethodHandle)}.
+ * @param combiner method handle to call initially on the incoming arguments
+ * @return method handle which incorporates the specified argument folding logic
+ * @throws NullPointerException if either argument is null
+ * @throws IllegalArgumentException if either of the following two conditions holds:
+ * (1) {@code combiner}'s return type is non-{@code void} and not the same as the argument type at position
+ * {@code pos} of the target signature;
+ * (2) the {@code N} argument types at position {@code pos} of the target signature (skipping one matching
+ * the {@code combiner}'s return type) are not identical with the argument types of {@code combiner}.
+ *
+ * @see #foldArguments(MethodHandle, MethodHandle)
+ * @since 9
+ */
+ public static
+ MethodHandle foldArguments(MethodHandle target, int pos, MethodHandle combiner) {
+ MethodType targetType = target.type();
+ MethodType combinerType = combiner.type();
+ Class<?> rtype = foldArgumentChecks(pos, targetType, combinerType);
+ // Android-changed: // Android-changed: transformer implementation.
+ // BoundMethodHandle result = target.rebind();
+ // boolean dropResult = rtype == void.class;
+ // LambdaForm lform = result.editor().foldArgumentsForm(1 + pos, dropResult, combinerType.basicType());
+ // MethodType newType = targetType;
+ // if (!dropResult) {
+ // newType = newType.dropParameterTypes(pos, pos + 1);
+ // }
+ // result = result.copyWithExtendL(newType, lform, combiner);
+ // return result;
+
+ return new Transformers.FoldArguments(target, pos, combiner);
+ }
+
+ private static Class<?> foldArgumentChecks(int foldPos, MethodType targetType, MethodType combinerType) {
+ int foldArgs = combinerType.parameterCount();
+ Class<?> rtype = combinerType.returnType();
+ int foldVals = rtype == void.class ? 0 : 1;
+ int afterInsertPos = foldPos + foldVals;
+ boolean ok = (targetType.parameterCount() >= afterInsertPos + foldArgs);
+ if (ok) {
+ for (int i = 0; i < foldArgs; i++) {
+ if (combinerType.parameterType(i) != targetType.parameterType(i + afterInsertPos)) {
+ ok = false;
+ break;
+ }
+ }
+ }
+ if (ok && foldVals != 0 && combinerType.returnType() != targetType.parameterType(foldPos))
+ ok = false;
+ if (!ok)
+ throw misMatchedTypes("target and combiner types", targetType, combinerType);
+ return rtype;
+ }
+
+ /**
+ * Makes a method handle which adapts a target method handle,
+ * by guarding it with a test, a boolean-valued method handle.
+ * If the guard fails, a fallback handle is called instead.
+ * All three method handles must have the same corresponding
+ * argument and return types, except that the return type
+ * of the test must be boolean, and the test is allowed
+ * to have fewer arguments than the other two method handles.
+ * <p> Here is pseudocode for the resulting adapter:
+ * <blockquote><pre>{@code
+ * boolean test(A...);
+ * T target(A...,B...);
+ * T fallback(A...,B...);
+ * T adapter(A... a,B... b) {
+ * if (test(a...))
+ * return target(a..., b...);
+ * else
+ * return fallback(a..., b...);
+ * }
+ * }</pre></blockquote>
+ * Note that the test arguments ({@code a...} in the pseudocode) cannot
+ * be modified by execution of the test, and so are passed unchanged
+ * from the caller to the target or fallback as appropriate.
+ * @param test method handle used for test, must return boolean
+ * @param target method handle to call if test passes
+ * @param fallback method handle to call if test fails
+ * @return method handle which incorporates the specified if/then/else logic
+ * @throws NullPointerException if any argument is null
+ * @throws IllegalArgumentException if {@code test} does not return boolean,
+ * or if all three method types do not match (with the return
+ * type of {@code test} changed to match that of the target).
+ */
+ public static
+ MethodHandle guardWithTest(MethodHandle test,
+ MethodHandle target,
+ MethodHandle fallback) {
+ MethodType gtype = test.type();
+ MethodType ttype = target.type();
+ MethodType ftype = fallback.type();
+ if (!ttype.equals(ftype))
+ throw misMatchedTypes("target and fallback types", ttype, ftype);
+ if (gtype.returnType() != boolean.class)
+ throw newIllegalArgumentException("guard type is not a predicate "+gtype);
+ List<Class<?>> targs = ttype.parameterList();
+ List<Class<?>> gargs = gtype.parameterList();
+ if (!targs.equals(gargs)) {
+ int gpc = gargs.size(), tpc = targs.size();
+ if (gpc >= tpc || !targs.subList(0, gpc).equals(gargs))
+ throw misMatchedTypes("target and test types", ttype, gtype);
+ test = dropArguments(test, gpc, targs.subList(gpc, tpc));
+ gtype = test.type();
+ }
+
+ return new Transformers.GuardWithTest(test, target, fallback);
+ }
+
+ static <T> RuntimeException misMatchedTypes(String what, T t1, T t2) {
+ return newIllegalArgumentException(what + " must match: " + t1 + " != " + t2);
+ }
+
+ /**
+ * Makes a method handle which adapts a target method handle,
+ * by running it inside an exception handler.
+ * If the target returns normally, the adapter returns that value.
+ * If an exception matching the specified type is thrown, the fallback
+ * handle is called instead on the exception, plus the original arguments.
+ * <p>
+ * The target and handler must have the same corresponding
+ * argument and return types, except that handler may omit trailing arguments
+ * (similarly to the predicate in {@link #guardWithTest guardWithTest}).
+ * Also, the handler must have an extra leading parameter of {@code exType} or a supertype.
+ * <p>
+ * Here is pseudocode for the resulting adapter. In the code, {@code T}
+ * represents the return type of the {@code target} and {@code handler},
+ * and correspondingly that of the resulting adapter; {@code A}/{@code a},
+ * the types and values of arguments to the resulting handle consumed by
+ * {@code handler}; and {@code B}/{@code b}, those of arguments to the
+ * resulting handle discarded by {@code handler}.
+ * <blockquote><pre>{@code
+ * T target(A..., B...);
+ * T handler(ExType, A...);
+ * T adapter(A... a, B... b) {
+ * try {
+ * return target(a..., b...);
+ * } catch (ExType ex) {
+ * return handler(ex, a...);
+ * }
+ * }
+ * }</pre></blockquote>
+ * Note that the saved arguments ({@code a...} in the pseudocode) cannot
+ * be modified by execution of the target, and so are passed unchanged
+ * from the caller to the handler, if the handler is invoked.
+ * <p>
+ * The target and handler must return the same type, even if the handler
+ * always throws. (This might happen, for instance, because the handler
+ * is simulating a {@code finally} clause).
+ * To create such a throwing handler, compose the handler creation logic
+ * with {@link #throwException throwException},
+ * in order to create a method handle of the correct return type.
+ * @param target method handle to call
+ * @param exType the type of exception which the handler will catch
+ * @param handler method handle to call if a matching exception is thrown
+ * @return method handle which incorporates the specified try/catch logic
+ * @throws NullPointerException if any argument is null
+ * @throws IllegalArgumentException if {@code handler} does not accept
+ * the given exception type, or if the method handle types do
+ * not match in their return types and their
+ * corresponding parameters
+ * @see MethodHandles#tryFinally(MethodHandle, MethodHandle)
+ */
+ public static
+ MethodHandle catchException(MethodHandle target,
+ Class<? extends Throwable> exType,
+ MethodHandle handler) {
+ MethodType ttype = target.type();
+ MethodType htype = handler.type();
+ if (!Throwable.class.isAssignableFrom(exType))
+ throw new ClassCastException(exType.getName());
+ if (htype.parameterCount() < 1 ||
+ !htype.parameterType(0).isAssignableFrom(exType))
+ throw newIllegalArgumentException("handler does not accept exception type "+exType);
+ if (htype.returnType() != ttype.returnType())
+ throw misMatchedTypes("target and handler return types", ttype, htype);
+ handler = dropArgumentsToMatch(handler, 1, ttype.parameterList(), 0, true);
+ if (handler == null) {
+ throw misMatchedTypes("target and handler types", ttype, htype);
+ }
+ // Android-changed: use Transformer implementation.
+ // return MethodHandleImpl.makeGuardWithCatch(target, exType, handler);
+ return new Transformers.CatchException(target, handler, exType);
+ }
+
+ /**
+ * Produces a method handle which will throw exceptions of the given {@code exType}.
+ * The method handle will accept a single argument of {@code exType},
+ * and immediately throw it as an exception.
+ * The method type will nominally specify a return of {@code returnType}.
+ * The return type may be anything convenient: It doesn't matter to the
+ * method handle's behavior, since it will never return normally.
+ * @param returnType the return type of the desired method handle
+ * @param exType the parameter type of the desired method handle
+ * @return method handle which can throw the given exceptions
+ * @throws NullPointerException if either argument is null
+ */
+ public static
+ MethodHandle throwException(Class<?> returnType, Class<? extends Throwable> exType) {
+ if (!Throwable.class.isAssignableFrom(exType))
+ throw new ClassCastException(exType.getName());
+ // Android-changed: use Transformer implementation.
+ // return MethodHandleImpl.throwException(methodType(returnType, exType));
+ return new Transformers.AlwaysThrow(returnType, exType);
+ }
+
+ /**
+ * Constructs a method handle representing a loop with several loop variables that are updated and checked upon each
+ * iteration. Upon termination of the loop due to one of the predicates, a corresponding finalizer is run and
+ * delivers the loop's result, which is the return value of the resulting handle.
+ * <p>
+ * Intuitively, every loop is formed by one or more "clauses", each specifying a local <em>iteration variable</em> and/or a loop
+ * exit. Each iteration of the loop executes each clause in order. A clause can optionally update its iteration
+ * variable; it can also optionally perform a test and conditional loop exit. In order to express this logic in
+ * terms of method handles, each clause will specify up to four independent actions:<ul>
+ * <li><em>init:</em> Before the loop executes, the initialization of an iteration variable {@code v} of type {@code V}.
+ * <li><em>step:</em> When a clause executes, an update step for the iteration variable {@code v}.
+ * <li><em>pred:</em> When a clause executes, a predicate execution to test for loop exit.
+ * <li><em>fini:</em> If a clause causes a loop exit, a finalizer execution to compute the loop's return value.
+ * </ul>
+ * The full sequence of all iteration variable types, in clause order, will be notated as {@code (V...)}.
+ * The values themselves will be {@code (v...)}. When we speak of "parameter lists", we will usually
+ * be referring to types, but in some contexts (describing execution) the lists will be of actual values.
+ * <p>
+ * Some of these clause parts may be omitted according to certain rules, and useful default behavior is provided in
+ * this case. See below for a detailed description.
+ * <p>
+ * <em>Parameters optional everywhere:</em>
+ * Each clause function is allowed but not required to accept a parameter for each iteration variable {@code v}.
+ * As an exception, the init functions cannot take any {@code v} parameters,
+ * because those values are not yet computed when the init functions are executed.
+ * Any clause function may neglect to take any trailing subsequence of parameters it is entitled to take.
+ * In fact, any clause function may take no arguments at all.
+ * <p>
+ * <em>Loop parameters:</em>
+ * A clause function may take all the iteration variable values it is entitled to, in which case
+ * it may also take more trailing parameters. Such extra values are called <em>loop parameters</em>,
+ * with their types and values notated as {@code (A...)} and {@code (a...)}.
+ * These become the parameters of the resulting loop handle, to be supplied whenever the loop is executed.
+ * (Since init functions do not accept iteration variables {@code v}, any parameter to an
+ * init function is automatically a loop parameter {@code a}.)
+ * As with iteration variables, clause functions are allowed but not required to accept loop parameters.
+ * These loop parameters act as loop-invariant values visible across the whole loop.
+ * <p>
+ * <em>Parameters visible everywhere:</em>
+ * Each non-init clause function is permitted to observe the entire loop state, because it can be passed the full
+ * list {@code (v... a...)} of current iteration variable values and incoming loop parameters.
+ * The init functions can observe initial pre-loop state, in the form {@code (a...)}.
+ * Most clause functions will not need all of this information, but they will be formally connected to it
+ * as if by {@link #dropArguments}.
+ * <a id="astar"></a>
+ * More specifically, we shall use the notation {@code (V*)} to express an arbitrary prefix of a full
+ * sequence {@code (V...)} (and likewise for {@code (v*)}, {@code (A*)}, {@code (a*)}).
+ * In that notation, the general form of an init function parameter list
+ * is {@code (A*)}, and the general form of a non-init function parameter list is {@code (V*)} or {@code (V... A*)}.
+ * <p>
+ * <em>Checking clause structure:</em>
+ * Given a set of clauses, there is a number of checks and adjustments performed to connect all the parts of the
+ * loop. They are spelled out in detail in the steps below. In these steps, every occurrence of the word "must"
+ * corresponds to a place where {@link IllegalArgumentException} will be thrown if the required constraint is not
+ * met by the inputs to the loop combinator.
+ * <p>
+ * <em>Effectively identical sequences:</em>
+ * <a id="effid"></a>
+ * A parameter list {@code A} is defined to be <em>effectively identical</em> to another parameter list {@code B}
+ * if {@code A} and {@code B} are identical, or if {@code A} is shorter and is identical with a proper prefix of {@code B}.
+ * When speaking of an unordered set of parameter lists, we say they the set is "effectively identical"
+ * as a whole if the set contains a longest list, and all members of the set are effectively identical to
+ * that longest list.
+ * For example, any set of type sequences of the form {@code (V*)} is effectively identical,
+ * and the same is true if more sequences of the form {@code (V... A*)} are added.
+ * <p>
+ * <em>Step 0: Determine clause structure.</em><ol type="a">
+ * <li>The clause array (of type {@code MethodHandle[][]}) must be non-{@code null} and contain at least one element.
+ * <li>The clause array may not contain {@code null}s or sub-arrays longer than four elements.
+ * <li>Clauses shorter than four elements are treated as if they were padded by {@code null} elements to length
+ * four. Padding takes place by appending elements to the array.
+ * <li>Clauses with all {@code null}s are disregarded.
+ * <li>Each clause is treated as a four-tuple of functions, called "init", "step", "pred", and "fini".
+ * </ol>
+ * <p>
+ * <em>Step 1A: Determine iteration variable types {@code (V...)}.</em><ol type="a">
+ * <li>The iteration variable type for each clause is determined using the clause's init and step return types.
+ * <li>If both functions are omitted, there is no iteration variable for the corresponding clause ({@code void} is
+ * used as the type to indicate that). If one of them is omitted, the other's return type defines the clause's
+ * iteration variable type. If both are given, the common return type (they must be identical) defines the clause's
+ * iteration variable type.
+ * <li>Form the list of return types (in clause order), omitting all occurrences of {@code void}.
+ * <li>This list of types is called the "iteration variable types" ({@code (V...)}).
+ * </ol>
+ * <p>
+ * <em>Step 1B: Determine loop parameters {@code (A...)}.</em><ul>
+ * <li>Examine and collect init function parameter lists (which are of the form {@code (A*)}).
+ * <li>Examine and collect the suffixes of the step, pred, and fini parameter lists, after removing the iteration variable types.
+ * (They must have the form {@code (V... A*)}; collect the {@code (A*)} parts only.)
+ * <li>Do not collect suffixes from step, pred, and fini parameter lists that do not begin with all the iteration variable types.
+ * (These types will be checked in step 2, along with all the clause function types.)
+ * <li>Omitted clause functions are ignored. (Equivalently, they are deemed to have empty parameter lists.)
+ * <li>All of the collected parameter lists must be effectively identical.
+ * <li>The longest parameter list (which is necessarily unique) is called the "external parameter list" ({@code (A...)}).
+ * <li>If there is no such parameter list, the external parameter list is taken to be the empty sequence.
+ * <li>The combined list consisting of iteration variable types followed by the external parameter types is called
+ * the "internal parameter list".
+ * </ul>
+ * <p>
+ * <em>Step 1C: Determine loop return type.</em><ol type="a">
+ * <li>Examine fini function return types, disregarding omitted fini functions.
+ * <li>If there are no fini functions, the loop return type is {@code void}.
+ * <li>Otherwise, the common return type {@code R} of the fini functions (their return types must be identical) defines the loop return
+ * type.
+ * </ol>
+ * <p>
+ * <em>Step 1D: Check other types.</em><ol type="a">
+ * <li>There must be at least one non-omitted pred function.
+ * <li>Every non-omitted pred function must have a {@code boolean} return type.
+ * </ol>
+ * <p>
+ * <em>Step 2: Determine parameter lists.</em><ol type="a">
+ * <li>The parameter list for the resulting loop handle will be the external parameter list {@code (A...)}.
+ * <li>The parameter list for init functions will be adjusted to the external parameter list.
+ * (Note that their parameter lists are already effectively identical to this list.)
+ * <li>The parameter list for every non-omitted, non-init (step, pred, and fini) function must be
+ * effectively identical to the internal parameter list {@code (V... A...)}.
+ * </ol>
+ * <p>
+ * <em>Step 3: Fill in omitted functions.</em><ol type="a">
+ * <li>If an init function is omitted, use a {@linkplain #empty default value} for the clause's iteration variable
+ * type.
+ * <li>If a step function is omitted, use an {@linkplain #identity identity function} of the clause's iteration
+ * variable type; insert dropped argument parameters before the identity function parameter for the non-{@code void}
+ * iteration variables of preceding clauses. (This will turn the loop variable into a local loop invariant.)
+ * <li>If a pred function is omitted, use a constant {@code true} function. (This will keep the loop going, as far
+ * as this clause is concerned. Note that in such cases the corresponding fini function is unreachable.)
+ * <li>If a fini function is omitted, use a {@linkplain #empty default value} for the
+ * loop return type.
+ * </ol>
+ * <p>
+ * <em>Step 4: Fill in missing parameter types.</em><ol type="a">
+ * <li>At this point, every init function parameter list is effectively identical to the external parameter list {@code (A...)},
+ * but some lists may be shorter. For every init function with a short parameter list, pad out the end of the list.
+ * <li>At this point, every non-init function parameter list is effectively identical to the internal parameter
+ * list {@code (V... A...)}, but some lists may be shorter. For every non-init function with a short parameter list,
+ * pad out the end of the list.
+ * <li>Argument lists are padded out by {@linkplain #dropArgumentsToMatch(MethodHandle, int, List, int) dropping unused trailing arguments}.
+ * </ol>
+ * <p>
+ * <em>Final observations.</em><ol type="a">
+ * <li>After these steps, all clauses have been adjusted by supplying omitted functions and arguments.
+ * <li>All init functions have a common parameter type list {@code (A...)}, which the final loop handle will also have.
+ * <li>All fini functions have a common return type {@code R}, which the final loop handle will also have.
+ * <li>All non-init functions have a common parameter type list {@code (V... A...)}, of
+ * (non-{@code void}) iteration variables {@code V} followed by loop parameters.
+ * <li>Each pair of init and step functions agrees in their return type {@code V}.
+ * <li>Each non-init function will be able to observe the current values {@code (v...)} of all iteration variables.
+ * <li>Every function will be able to observe the incoming values {@code (a...)} of all loop parameters.
+ * </ol>
+ * <p>
+ * <em>Example.</em> As a consequence of step 1A above, the {@code loop} combinator has the following property:
+ * <ul>
+ * <li>Given {@code N} clauses {@code Cn = {null, Sn, Pn}} with {@code n = 1..N}.
+ * <li>Suppose predicate handles {@code Pn} are either {@code null} or have no parameters.
+ * (Only one {@code Pn} has to be non-{@code null}.)
+ * <li>Suppose step handles {@code Sn} have signatures {@code (B1..BX)Rn}, for some constant {@code X>=N}.
+ * <li>Suppose {@code Q} is the count of non-void types {@code Rn}, and {@code (V1...VQ)} is the sequence of those types.
+ * <li>It must be that {@code Vn == Bn} for {@code n = 1..min(X,Q)}.
+ * <li>The parameter types {@code Vn} will be interpreted as loop-local state elements {@code (V...)}.
+ * <li>Any remaining types {@code BQ+1..BX} (if {@code Q<X}) will determine
+ * the resulting loop handle's parameter types {@code (A...)}.
+ * </ul>
+ * In this example, the loop handle parameters {@code (A...)} were derived from the step functions,
+ * which is natural if most of the loop computation happens in the steps. For some loops,
+ * the burden of computation might be heaviest in the pred functions, and so the pred functions
+ * might need to accept the loop parameter values. For loops with complex exit logic, the fini
+ * functions might need to accept loop parameters, and likewise for loops with complex entry logic,
+ * where the init functions will need the extra parameters. For such reasons, the rules for
+ * determining these parameters are as symmetric as possible, across all clause parts.
+ * In general, the loop parameters function as common invariant values across the whole
+ * loop, while the iteration variables function as common variant values, or (if there is
+ * no step function) as internal loop invariant temporaries.
+ * <p>
+ * <em>Loop execution.</em><ol type="a">
+ * <li>When the loop is called, the loop input values are saved in locals, to be passed to
+ * every clause function. These locals are loop invariant.
+ * <li>Each init function is executed in clause order (passing the external arguments {@code (a...)})
+ * and the non-{@code void} values are saved (as the iteration variables {@code (v...)}) into locals.
+ * These locals will be loop varying (unless their steps behave as identity functions, as noted above).
+ * <li>All function executions (except init functions) will be passed the internal parameter list, consisting of
+ * the non-{@code void} iteration values {@code (v...)} (in clause order) and then the loop inputs {@code (a...)}
+ * (in argument order).
+ * <li>The step and pred functions are then executed, in clause order (step before pred), until a pred function
+ * returns {@code false}.
+ * <li>The non-{@code void} result from a step function call is used to update the corresponding value in the
+ * sequence {@code (v...)} of loop variables.
+ * The updated value is immediately visible to all subsequent function calls.
+ * <li>If a pred function returns {@code false}, the corresponding fini function is called, and the resulting value
+ * (of type {@code R}) is returned from the loop as a whole.
+ * <li>If all the pred functions always return true, no fini function is ever invoked, and the loop cannot exit
+ * except by throwing an exception.
+ * </ol>
+ * <p>
+ * <em>Usage tips.</em>
+ * <ul>
+ * <li>Although each step function will receive the current values of <em>all</em> the loop variables,
+ * sometimes a step function only needs to observe the current value of its own variable.
+ * In that case, the step function may need to explicitly {@linkplain #dropArguments drop all preceding loop variables}.
+ * This will require mentioning their types, in an expression like {@code dropArguments(step, 0, V0.class, ...)}.
+ * <li>Loop variables are not required to vary; they can be loop invariant. A clause can create
+ * a loop invariant by a suitable init function with no step, pred, or fini function. This may be
+ * useful to "wire" an incoming loop argument into the step or pred function of an adjacent loop variable.
+ * <li>If some of the clause functions are virtual methods on an instance, the instance
+ * itself can be conveniently placed in an initial invariant loop "variable", using an initial clause
+ * like {@code new MethodHandle[]{identity(ObjType.class)}}. In that case, the instance reference
+ * will be the first iteration variable value, and it will be easy to use virtual
+ * methods as clause parts, since all of them will take a leading instance reference matching that value.
+ * </ul>
+ * <p>
+ * Here is pseudocode for the resulting loop handle. As above, {@code V} and {@code v} represent the types
+ * and values of loop variables; {@code A} and {@code a} represent arguments passed to the whole loop;
+ * and {@code R} is the common result type of all finalizers as well as of the resulting loop.
+ * <blockquote><pre>{@code
+ * V... init...(A...);
+ * boolean pred...(V..., A...);
+ * V... step...(V..., A...);
+ * R fini...(V..., A...);
+ * R loop(A... a) {
+ * V... v... = init...(a...);
+ * for (;;) {
+ * for ((v, p, s, f) in (v..., pred..., step..., fini...)) {
+ * v = s(v..., a...);
+ * if (!p(v..., a...)) {
+ * return f(v..., a...);
+ * }
+ * }
+ * }
+ * }
+ * }</pre></blockquote>
+ * Note that the parameter type lists {@code (V...)} and {@code (A...)} have been expanded
+ * to their full length, even though individual clause functions may neglect to take them all.
+ * As noted above, missing parameters are filled in as if by {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}.
+ *
+ * @apiNote Example:
+ * <blockquote><pre>{@code
+ * // iterative implementation of the factorial function as a loop handle
+ * static int one(int k) { return 1; }
+ * static int inc(int i, int acc, int k) { return i + 1; }
+ * static int mult(int i, int acc, int k) { return i * acc; }
+ * static boolean pred(int i, int acc, int k) { return i < k; }
+ * static int fin(int i, int acc, int k) { return acc; }
+ * // assume MH_one, MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
+ * // null initializer for counter, should initialize to 0
+ * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
+ * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
+ * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
+ * assertEquals(120, loop.invoke(5));
+ * }</pre></blockquote>
+ * The same example, dropping arguments and using combinators:
+ * <blockquote><pre>{@code
+ * // simplified implementation of the factorial function as a loop handle
+ * static int inc(int i) { return i + 1; } // drop acc, k
+ * static int mult(int i, int acc) { return i * acc; } //drop k
+ * static boolean cmp(int i, int k) { return i < k; }
+ * // assume MH_inc, MH_mult, and MH_cmp are handles to the above methods
+ * // null initializer for counter, should initialize to 0
+ * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
+ * MethodHandle MH_pred = MethodHandles.dropArguments(MH_cmp, 1, int.class); // drop acc
+ * MethodHandle MH_fin = MethodHandles.dropArguments(MethodHandles.identity(int.class), 0, int.class); // drop i
+ * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
+ * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
+ * MethodHandle loop = MethodHandles.loop(counterClause, accumulatorClause);
+ * assertEquals(720, loop.invoke(6));
+ * }</pre></blockquote>
+ * A similar example, using a helper object to hold a loop parameter:
+ * <blockquote><pre>{@code
+ * // instance-based implementation of the factorial function as a loop handle
+ * static class FacLoop {
+ * final int k;
+ * FacLoop(int k) { this.k = k; }
+ * int inc(int i) { return i + 1; }
+ * int mult(int i, int acc) { return i * acc; }
+ * boolean pred(int i) { return i < k; }
+ * int fin(int i, int acc) { return acc; }
+ * }
+ * // assume MH_FacLoop is a handle to the constructor
+ * // assume MH_inc, MH_mult, MH_pred, and MH_fin are handles to the above methods
+ * // null initializer for counter, should initialize to 0
+ * MethodHandle MH_one = MethodHandles.constant(int.class, 1);
+ * MethodHandle[] instanceClause = new MethodHandle[]{MH_FacLoop};
+ * MethodHandle[] counterClause = new MethodHandle[]{null, MH_inc};
+ * MethodHandle[] accumulatorClause = new MethodHandle[]{MH_one, MH_mult, MH_pred, MH_fin};
+ * MethodHandle loop = MethodHandles.loop(instanceClause, counterClause, accumulatorClause);
+ * assertEquals(5040, loop.invoke(7));
+ * }</pre></blockquote>
+ *
+ * @param clauses an array of arrays (4-tuples) of {@link MethodHandle}s adhering to the rules described above.
+ *
+ * @return a method handle embodying the looping behavior as defined by the arguments.
+ *
+ * @throws IllegalArgumentException in case any of the constraints described above is violated.
+ *
+ * @see MethodHandles#whileLoop(MethodHandle, MethodHandle, MethodHandle)
+ * @see MethodHandles#doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
+ * @see MethodHandles#countedLoop(MethodHandle, MethodHandle, MethodHandle)
+ * @see MethodHandles#iteratedLoop(MethodHandle, MethodHandle, MethodHandle)
+ * @since 9
+ */
+ public static MethodHandle loop(MethodHandle[]... clauses) {
+ // Step 0: determine clause structure.
+ loopChecks0(clauses);
+
+ List<MethodHandle> init = new ArrayList<>();
+ List<MethodHandle> step = new ArrayList<>();
+ List<MethodHandle> pred = new ArrayList<>();
+ List<MethodHandle> fini = new ArrayList<>();
+
+ Stream.of(clauses).filter(c -> Stream.of(c).anyMatch(Objects::nonNull)).forEach(clause -> {
+ init.add(clause[0]); // all clauses have at least length 1
+ step.add(clause.length <= 1 ? null : clause[1]);
+ pred.add(clause.length <= 2 ? null : clause[2]);
+ fini.add(clause.length <= 3 ? null : clause[3]);
+ });
+
+ assert Stream.of(init, step, pred, fini).map(List::size).distinct().count() == 1;
+ final int nclauses = init.size();
+
+ // Step 1A: determine iteration variables (V...).
+ final List<Class<?>> iterationVariableTypes = new ArrayList<>();
+ for (int i = 0; i < nclauses; ++i) {
+ MethodHandle in = init.get(i);
+ MethodHandle st = step.get(i);
+ if (in == null && st == null) {
+ iterationVariableTypes.add(void.class);
+ } else if (in != null && st != null) {
+ loopChecks1a(i, in, st);
+ iterationVariableTypes.add(in.type().returnType());
+ } else {
+ iterationVariableTypes.add(in == null ? st.type().returnType() : in.type().returnType());
+ }
+ }
+ final List<Class<?>> commonPrefix = iterationVariableTypes.stream().filter(t -> t != void.class).
+ collect(Collectors.toList());
+
+ // Step 1B: determine loop parameters (A...).
+ final List<Class<?>> commonSuffix = buildCommonSuffix(init, step, pred, fini, commonPrefix.size());
+ loopChecks1b(init, commonSuffix);
+
+ // Step 1C: determine loop return type.
+ // Step 1D: check other types.
+ // local variable required here; see JDK-8223553
+ Stream<Class<?>> cstream = fini.stream().filter(Objects::nonNull).map(MethodHandle::type)
+ .map(MethodType::returnType);
+ final Class<?> loopReturnType = cstream.findFirst().orElse(void.class);
+ loopChecks1cd(pred, fini, loopReturnType);
+
+ // Step 2: determine parameter lists.
+ final List<Class<?>> commonParameterSequence = new ArrayList<>(commonPrefix);
+ commonParameterSequence.addAll(commonSuffix);
+ loopChecks2(step, pred, fini, commonParameterSequence);
+
+ // Step 3: fill in omitted functions.
+ for (int i = 0; i < nclauses; ++i) {
+ Class<?> t = iterationVariableTypes.get(i);
+ if (init.get(i) == null) {
+ init.set(i, empty(methodType(t, commonSuffix)));
+ }
+ if (step.get(i) == null) {
+ step.set(i, dropArgumentsToMatch(identityOrVoid(t), 0, commonParameterSequence, i));
+ }
+ if (pred.get(i) == null) {
+ pred.set(i, dropArguments0(constant(boolean.class, true), 0, commonParameterSequence));
+ }
+ if (fini.get(i) == null) {
+ fini.set(i, empty(methodType(t, commonParameterSequence)));
+ }
+ }
+
+ // Step 4: fill in missing parameter types.
+ // Also convert all handles to fixed-arity handles.
+ List<MethodHandle> finit = fixArities(fillParameterTypes(init, commonSuffix));
+ List<MethodHandle> fstep = fixArities(fillParameterTypes(step, commonParameterSequence));
+ List<MethodHandle> fpred = fixArities(fillParameterTypes(pred, commonParameterSequence));
+ List<MethodHandle> ffini = fixArities(fillParameterTypes(fini, commonParameterSequence));
+
+ assert finit.stream().map(MethodHandle::type).map(MethodType::parameterList).
+ allMatch(pl -> pl.equals(commonSuffix));
+ assert Stream.of(fstep, fpred, ffini).flatMap(List::stream).map(MethodHandle::type).map(MethodType::parameterList).
+ allMatch(pl -> pl.equals(commonParameterSequence));
+
+ // Android-changed: transformer implementation.
+ // return MethodHandleImpl.makeLoop(loopReturnType, commonSuffix, finit, fstep, fpred, ffini);
+ return new Transformers.Loop(loopReturnType,
+ commonSuffix,
+ finit.toArray(MethodHandle[]::new),
+ fstep.toArray(MethodHandle[]::new),
+ fpred.toArray(MethodHandle[]::new),
+ ffini.toArray(MethodHandle[]::new));
+ }
+
+ private static void loopChecks0(MethodHandle[][] clauses) {
+ if (clauses == null || clauses.length == 0) {
+ throw newIllegalArgumentException("null or no clauses passed");
+ }
+ if (Stream.of(clauses).anyMatch(Objects::isNull)) {
+ throw newIllegalArgumentException("null clauses are not allowed");
+ }
+ if (Stream.of(clauses).anyMatch(c -> c.length > 4)) {
+ throw newIllegalArgumentException("All loop clauses must be represented as MethodHandle arrays with at most 4 elements.");
+ }
+ }
+
+ private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
+ if (in.type().returnType() != st.type().returnType()) {
+ throw misMatchedTypes("clause " + i + ": init and step return types", in.type().returnType(),
+ st.type().returnType());
+ }
+ }
+
+ private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
+ final List<Class<?>> empty = List.of();
+ final List<Class<?>> longest = mhs.filter(Objects::nonNull).
+ // take only those that can contribute to a common suffix because they are longer than the prefix
+ map(MethodHandle::type).
+ filter(t -> t.parameterCount() > skipSize).
+ map(MethodType::parameterList).
+ reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
+ return longest.size() == 0 ? empty : longest.subList(skipSize, longest.size());
+ }
+
+ private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
+ final List<Class<?>> empty = List.of();
+ return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
+ }
+
+ private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
+ final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
+ final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
+ return longestParameterList(Arrays.asList(longest1, longest2));
+ }
+
+ private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {
+ if (init.stream().filter(Objects::nonNull).map(MethodHandle::type).
+ anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonSuffix))) {
+ throw newIllegalArgumentException("found non-effectively identical init parameter type lists: " + init +
+ " (common suffix: " + commonSuffix + ")");
+ }
+ }
+
+ private static void loopChecks1cd(List<MethodHandle> pred, List<MethodHandle> fini, Class<?> loopReturnType) {
+ if (fini.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
+ anyMatch(t -> t != loopReturnType)) {
+ throw newIllegalArgumentException("found non-identical finalizer return types: " + fini + " (return type: " +
+ loopReturnType + ")");
+ }
+
+ if (!pred.stream().filter(Objects::nonNull).findFirst().isPresent()) {
+ throw newIllegalArgumentException("no predicate found", pred);
+ }
+ if (pred.stream().filter(Objects::nonNull).map(MethodHandle::type).map(MethodType::returnType).
+ anyMatch(t -> t != boolean.class)) {
+ throw newIllegalArgumentException("predicates must have boolean return type", pred);
+ }
+ }
+
+ private static void loopChecks2(List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, List<Class<?>> commonParameterSequence) {
+ if (Stream.of(step, pred, fini).flatMap(List::stream).filter(Objects::nonNull).map(MethodHandle::type).
+ anyMatch(t -> !t.effectivelyIdenticalParameters(0, commonParameterSequence))) {
+ throw newIllegalArgumentException("found non-effectively identical parameter type lists:\nstep: " + step +
+ "\npred: " + pred + "\nfini: " + fini + " (common parameter sequence: " + commonParameterSequence + ")");
+ }
+ }
+
+ private static List<MethodHandle> fillParameterTypes(List<MethodHandle> hs, final List<Class<?>> targetParams) {
+ return hs.stream().map(h -> {
+ int pc = h.type().parameterCount();
+ int tpsize = targetParams.size();
+ return pc < tpsize ? dropArguments0(h, pc, targetParams.subList(pc, tpsize)) : h;
+ }).collect(Collectors.toList());
+ }
+
+ private static List<MethodHandle> fixArities(List<MethodHandle> hs) {
+ return hs.stream().map(MethodHandle::asFixedArity).collect(Collectors.toList());
+ }
+
+ /**
+ * Constructs a {@code while} loop from an initializer, a body, and a predicate.
+ * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
+ * <p>
+ * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
+ * method will, in each iteration, first evaluate the predicate and then execute its body (if the predicate
+ * evaluates to {@code true}).
+ * The loop will terminate once the predicate evaluates to {@code false} (the body will not be executed in this case).
+ * <p>
+ * The {@code init} handle describes the initial value of an additional optional loop-local variable.
+ * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
+ * and updated with the value returned from its invocation. The result of loop execution will be
+ * the final value of the additional loop-local variable (if present).
+ * <p>
+ * The following rules hold for these argument handles:<ul>
+ * <li>The {@code body} handle must not be {@code null}; its type must be of the form
+ * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
+ * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
+ * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
+ * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
+ * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
+ * It will constrain the parameter lists of the other loop parts.
+ * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
+ * list {@code (A...)} is called the <em>external parameter list</em>.
+ * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
+ * additional state variable of the loop.
+ * The body must both accept and return a value of this type {@code V}.
+ * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
+ * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
+ * <a href="MethodHandles.html#effid">effectively identical</a>
+ * to the external parameter list {@code (A...)}.
+ * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
+ * {@linkplain #empty default value}.
+ * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
+ * Its parameter list (either empty or of the form {@code (V A*)}) must be
+ * effectively identical to the internal parameter list.
+ * </ul>
+ * <p>
+ * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
+ * <li>The loop handle's result type is the result type {@code V} of the body.
+ * <li>The loop handle's parameter types are the types {@code (A...)},
+ * from the external parameter list.
+ * </ul>
+ * <p>
+ * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
+ * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
+ * passed to the loop.
+ * <blockquote><pre>{@code
+ * V init(A...);
+ * boolean pred(V, A...);
+ * V body(V, A...);
+ * V whileLoop(A... a...) {
+ * V v = init(a...);
+ * while (pred(v, a...)) {
+ * v = body(v, a...);
+ * }
+ * return v;
+ * }
+ * }</pre></blockquote>
+ *
+ * @apiNote Example:
+ * <blockquote><pre>{@code
+ * // implement the zip function for lists as a loop handle
+ * static List<String> initZip(Iterator<String> a, Iterator<String> b) { return new ArrayList<>(); }
+ * static boolean zipPred(List<String> zip, Iterator<String> a, Iterator<String> b) { return a.hasNext() && b.hasNext(); }
+ * static List<String> zipStep(List<String> zip, Iterator<String> a, Iterator<String> b) {
+ * zip.add(a.next());
+ * zip.add(b.next());
+ * return zip;
+ * }
+ * // assume MH_initZip, MH_zipPred, and MH_zipStep are handles to the above methods
+ * MethodHandle loop = MethodHandles.whileLoop(MH_initZip, MH_zipPred, MH_zipStep);
+ * List<String> a = Arrays.asList("a", "b", "c", "d");
+ * List<String> b = Arrays.asList("e", "f", "g", "h");
+ * List<String> zipped = Arrays.asList("a", "e", "b", "f", "c", "g", "d", "h");
+ * assertEquals(zipped, (List<String>) loop.invoke(a.iterator(), b.iterator()));
+ * }</pre></blockquote>
+ *
+ *
+ * @apiNote The implementation of this method can be expressed as follows:
+ * <blockquote><pre>{@code
+ * MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
+ * MethodHandle fini = (body.type().returnType() == void.class
+ * ? null : identity(body.type().returnType()));
+ * MethodHandle[]
+ * checkExit = { null, null, pred, fini },
+ * varBody = { init, body };
+ * return loop(checkExit, varBody);
+ * }
+ * }</pre></blockquote>
+ *
+ * @param init optional initializer, providing the initial value of the loop variable.
+ * May be {@code null}, implying a default initial value. See above for other constraints.
+ * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
+ * above for other constraints.
+ * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
+ * See above for other constraints.
+ *
+ * @return a method handle implementing the {@code while} loop as described by the arguments.
+ * @throws IllegalArgumentException if the rules for the arguments are violated.
+ * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
+ *
+ * @see #loop(MethodHandle[][])
+ * @see #doWhileLoop(MethodHandle, MethodHandle, MethodHandle)
+ * @since 9
+ */
+ public static MethodHandle whileLoop(MethodHandle init, MethodHandle pred, MethodHandle body) {
+ whileLoopChecks(init, pred, body);
+ MethodHandle fini = identityOrVoid(body.type().returnType());
+ MethodHandle[] checkExit = { null, null, pred, fini };
+ MethodHandle[] varBody = { init, body };
+ return loop(checkExit, varBody);
+ }
+
+ /**
+ * Constructs a {@code do-while} loop from an initializer, a body, and a predicate.
+ * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
+ * <p>
+ * The {@code pred} handle describes the loop condition; and {@code body}, its body. The loop resulting from this
+ * method will, in each iteration, first execute its body and then evaluate the predicate.
+ * The loop will terminate once the predicate evaluates to {@code false} after an execution of the body.
+ * <p>
+ * The {@code init} handle describes the initial value of an additional optional loop-local variable.
+ * In each iteration, this loop-local variable, if present, will be passed to the {@code body}
+ * and updated with the value returned from its invocation. The result of loop execution will be
+ * the final value of the additional loop-local variable (if present).
+ * <p>
+ * The following rules hold for these argument handles:<ul>
+ * <li>The {@code body} handle must not be {@code null}; its type must be of the form
+ * {@code (V A...)V}, where {@code V} is non-{@code void}, or else {@code (A...)void}.
+ * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
+ * and we will write {@code (V A...)V} with the understanding that a {@code void} type {@code V}
+ * is quietly dropped from the parameter list, leaving {@code (A...)V}.)
+ * <li>The parameter list {@code (V A...)} of the body is called the <em>internal parameter list</em>.
+ * It will constrain the parameter lists of the other loop parts.
+ * <li>If the iteration variable type {@code V} is dropped from the internal parameter list, the resulting shorter
+ * list {@code (A...)} is called the <em>external parameter list</em>.
+ * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
+ * additional state variable of the loop.
+ * The body must both accept and return a value of this type {@code V}.
+ * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
+ * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
+ * <a href="MethodHandles.html#effid">effectively identical</a>
+ * to the external parameter list {@code (A...)}.
+ * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
+ * {@linkplain #empty default value}.
+ * <li>The {@code pred} handle must not be {@code null}. It must have {@code boolean} as its return type.
+ * Its parameter list (either empty or of the form {@code (V A*)}) must be
+ * effectively identical to the internal parameter list.
+ * </ul>
+ * <p>
+ * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
+ * <li>The loop handle's result type is the result type {@code V} of the body.
+ * <li>The loop handle's parameter types are the types {@code (A...)},
+ * from the external parameter list.
+ * </ul>
+ * <p>
+ * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
+ * the sole loop variable as well as the result type of the loop; and {@code A}/{@code a}, that of the argument
+ * passed to the loop.
+ * <blockquote><pre>{@code
+ * V init(A...);
+ * boolean pred(V, A...);
+ * V body(V, A...);
+ * V doWhileLoop(A... a...) {
+ * V v = init(a...);
+ * do {
+ * v = body(v, a...);
+ * } while (pred(v, a...));
+ * return v;
+ * }
+ * }</pre></blockquote>
+ *
+ * @apiNote Example:
+ * <blockquote><pre>{@code
+ * // int i = 0; while (i < limit) { ++i; } return i; => limit
+ * static int zero(int limit) { return 0; }
+ * static int step(int i, int limit) { return i + 1; }
+ * static boolean pred(int i, int limit) { return i < limit; }
+ * // assume MH_zero, MH_step, and MH_pred are handles to the above methods
+ * MethodHandle loop = MethodHandles.doWhileLoop(MH_zero, MH_step, MH_pred);
+ * assertEquals(23, loop.invoke(23));
+ * }</pre></blockquote>
+ *
+ *
+ * @apiNote The implementation of this method can be expressed as follows:
+ * <blockquote><pre>{@code
+ * MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
+ * MethodHandle fini = (body.type().returnType() == void.class
+ * ? null : identity(body.type().returnType()));
+ * MethodHandle[] clause = { init, body, pred, fini };
+ * return loop(clause);
+ * }
+ * }</pre></blockquote>
+ *
+ * @param init optional initializer, providing the initial value of the loop variable.
+ * May be {@code null}, implying a default initial value. See above for other constraints.
+ * @param body body of the loop, which may not be {@code null}. It controls the loop parameters and result type.
+ * See above for other constraints.
+ * @param pred condition for the loop, which may not be {@code null}. Its result type must be {@code boolean}. See
+ * above for other constraints.
+ *
+ * @return a method handle implementing the {@code while} loop as described by the arguments.
+ * @throws IllegalArgumentException if the rules for the arguments are violated.
+ * @throws NullPointerException if {@code pred} or {@code body} are {@code null}.
+ *
+ * @see #loop(MethodHandle[][])
+ * @see #whileLoop(MethodHandle, MethodHandle, MethodHandle)
+ * @since 9
+ */
+ public static MethodHandle doWhileLoop(MethodHandle init, MethodHandle body, MethodHandle pred) {
+ whileLoopChecks(init, pred, body);
+ MethodHandle fini = identityOrVoid(body.type().returnType());
+ MethodHandle[] clause = {init, body, pred, fini };
+ return loop(clause);
+ }
+
+ private static void whileLoopChecks(MethodHandle init, MethodHandle pred, MethodHandle body) {
+ Objects.requireNonNull(pred);
+ Objects.requireNonNull(body);
+ MethodType bodyType = body.type();
+ Class<?> returnType = bodyType.returnType();
+ List<Class<?>> innerList = bodyType.parameterList();
+ List<Class<?>> outerList = innerList;
+ if (returnType == void.class) {
+ // OK
+ } else if (innerList.size() == 0 || innerList.get(0) != returnType) {
+ // leading V argument missing => error
+ MethodType expected = bodyType.insertParameterTypes(0, returnType);
+ throw misMatchedTypes("body function", bodyType, expected);
+ } else {
+ outerList = innerList.subList(1, innerList.size());
+ }
+ MethodType predType = pred.type();
+ if (predType.returnType() != boolean.class ||
+ !predType.effectivelyIdenticalParameters(0, innerList)) {
+ throw misMatchedTypes("loop predicate", predType, methodType(boolean.class, innerList));
+ }
+ if (init != null) {
+ MethodType initType = init.type();
+ if (initType.returnType() != returnType ||
+ !initType.effectivelyIdenticalParameters(0, outerList)) {
+ throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
+ }
+ }
+ }
+
+ /**
+ * Constructs a loop that runs a given number of iterations.
+ * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
+ * <p>
+ * The number of iterations is determined by the {@code iterations} handle evaluation result.
+ * The loop counter {@code i} is an extra loop iteration variable of type {@code int}.
+ * It will be initialized to 0 and incremented by 1 in each iteration.
+ * <p>
+ * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
+ * of that type is also present. This variable is initialized using the optional {@code init} handle,
+ * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
+ * <p>
+ * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
+ * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
+ * iteration variable.
+ * The result of the loop handle execution will be the final {@code V} value of that variable
+ * (or {@code void} if there is no {@code V} variable).
+ * <p>
+ * The following rules hold for the argument handles:<ul>
+ * <li>The {@code iterations} handle must not be {@code null}, and must return
+ * the type {@code int}, referred to here as {@code I} in parameter type lists.
+ * <li>The {@code body} handle must not be {@code null}; its type must be of the form
+ * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
+ * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
+ * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
+ * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
+ * <li>The parameter list {@code (V I A...)} of the body contributes to a list
+ * of types called the <em>internal parameter list</em>.
+ * It will constrain the parameter lists of the other loop parts.
+ * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
+ * with no additional {@code A} types, then the internal parameter list is extended by
+ * the argument types {@code A...} of the {@code iterations} handle.
+ * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
+ * list {@code (A...)} is called the <em>external parameter list</em>.
+ * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
+ * additional state variable of the loop.
+ * The body must both accept a leading parameter and return a value of this type {@code V}.
+ * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
+ * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
+ * <a href="MethodHandles.html#effid">effectively identical</a>
+ * to the external parameter list {@code (A...)}.
+ * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
+ * {@linkplain #empty default value}.
+ * <li>The parameter list of {@code iterations} (of some form {@code (A*)}) must be
+ * effectively identical to the external parameter list {@code (A...)}.
+ * </ul>
+ * <p>
+ * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
+ * <li>The loop handle's result type is the result type {@code V} of the body.
+ * <li>The loop handle's parameter types are the types {@code (A...)},
+ * from the external parameter list.
+ * </ul>
+ * <p>
+ * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
+ * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
+ * arguments passed to the loop.
+ * <blockquote><pre>{@code
+ * int iterations(A...);
+ * V init(A...);
+ * V body(V, int, A...);
+ * V countedLoop(A... a...) {
+ * int end = iterations(a...);
+ * V v = init(a...);
+ * for (int i = 0; i < end; ++i) {
+ * v = body(v, i, a...);
+ * }
+ * return v;
+ * }
+ * }</pre></blockquote>
+ *
+ * @apiNote Example with a fully conformant body method:
+ * <blockquote><pre>{@code
+ * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
+ * // => a variation on a well known theme
+ * static String step(String v, int counter, String init) { return "na " + v; }
+ * // assume MH_step is a handle to the method above
+ * MethodHandle fit13 = MethodHandles.constant(int.class, 13);
+ * MethodHandle start = MethodHandles.identity(String.class);
+ * MethodHandle loop = MethodHandles.countedLoop(fit13, start, MH_step);
+ * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("Lambdaman!"));
+ * }</pre></blockquote>
+ *
+ * @apiNote Example with the simplest possible body method type,
+ * and passing the number of iterations to the loop invocation:
+ * <blockquote><pre>{@code
+ * // String s = "Lambdaman!"; for (int i = 0; i < 13; ++i) { s = "na " + s; } return s;
+ * // => a variation on a well known theme
+ * static String step(String v, int counter ) { return "na " + v; }
+ * // assume MH_step is a handle to the method above
+ * MethodHandle count = MethodHandles.dropArguments(MethodHandles.identity(int.class), 1, String.class);
+ * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class);
+ * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i) -> "na " + v
+ * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "Lambdaman!"));
+ * }</pre></blockquote>
+ *
+ * @apiNote Example that treats the number of iterations, string to append to, and string to append
+ * as loop parameters:
+ * <blockquote><pre>{@code
+ * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
+ * // => a variation on a well known theme
+ * static String step(String v, int counter, int iterations_, String pre, String start_) { return pre + " " + v; }
+ * // assume MH_step is a handle to the method above
+ * MethodHandle count = MethodHandles.identity(int.class);
+ * MethodHandle start = MethodHandles.dropArguments(MethodHandles.identity(String.class), 0, int.class, String.class);
+ * MethodHandle loop = MethodHandles.countedLoop(count, start, MH_step); // (v, i, _, pre, _) -> pre + " " + v
+ * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke(13, "na", "Lambdaman!"));
+ * }</pre></blockquote>
+ *
+ * @apiNote Example that illustrates the usage of {@link #dropArgumentsToMatch(MethodHandle, int, List, int)}
+ * to enforce a loop type:
+ * <blockquote><pre>{@code
+ * // String s = "Lambdaman!", t = "na"; for (int i = 0; i < 13; ++i) { s = t + " " + s; } return s;
+ * // => a variation on a well known theme
+ * static String step(String v, int counter, String pre) { return pre + " " + v; }
+ * // assume MH_step is a handle to the method above
+ * MethodType loopType = methodType(String.class, String.class, int.class, String.class);
+ * MethodHandle count = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(int.class), 0, loopType.parameterList(), 1);
+ * MethodHandle start = MethodHandles.dropArgumentsToMatch(MethodHandles.identity(String.class), 0, loopType.parameterList(), 2);
+ * MethodHandle body = MethodHandles.dropArgumentsToMatch(MH_step, 2, loopType.parameterList(), 0);
+ * MethodHandle loop = MethodHandles.countedLoop(count, start, body); // (v, i, pre, _, _) -> pre + " " + v
+ * assertEquals("na na na na na na na na na na na na na Lambdaman!", loop.invoke("na", 13, "Lambdaman!"));
+ * }</pre></blockquote>
+ *
+ * @apiNote The implementation of this method can be expressed as follows:
+ * <blockquote><pre>{@code
+ * MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
+ * return countedLoop(empty(iterations.type()), iterations, init, body);
+ * }
+ * }</pre></blockquote>
+ *
+ * @param iterations a non-{@code null} handle to return the number of iterations this loop should run. The handle's
+ * result type must be {@code int}. See above for other constraints.
+ * @param init optional initializer, providing the initial value of the loop variable.
+ * May be {@code null}, implying a default initial value. See above for other constraints.
+ * @param body body of the loop, which may not be {@code null}.
+ * It controls the loop parameters and result type in the standard case (see above for details).
+ * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
+ * and may accept any number of additional types.
+ * See above for other constraints.
+ *
+ * @return a method handle representing the loop.
+ * @throws NullPointerException if either of the {@code iterations} or {@code body} handles is {@code null}.
+ * @throws IllegalArgumentException if any argument violates the rules formulated above.
+ *
+ * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle, MethodHandle)
+ * @since 9
+ */
+ public static MethodHandle countedLoop(MethodHandle iterations, MethodHandle init, MethodHandle body) {
+ return countedLoop(empty(iterations.type()), iterations, init, body);
+ }
+
+ /**
+ * Constructs a loop that counts over a range of numbers.
+ * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
+ * <p>
+ * The loop counter {@code i} is a loop iteration variable of type {@code int}.
+ * The {@code start} and {@code end} handles determine the start (inclusive) and end (exclusive)
+ * values of the loop counter.
+ * The loop counter will be initialized to the {@code int} value returned from the evaluation of the
+ * {@code start} handle and run to the value returned from {@code end} (exclusively) with a step width of 1.
+ * <p>
+ * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
+ * of that type is also present. This variable is initialized using the optional {@code init} handle,
+ * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
+ * <p>
+ * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
+ * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
+ * iteration variable.
+ * The result of the loop handle execution will be the final {@code V} value of that variable
+ * (or {@code void} if there is no {@code V} variable).
+ * <p>
+ * The following rules hold for the argument handles:<ul>
+ * <li>The {@code start} and {@code end} handles must not be {@code null}, and must both return
+ * the common type {@code int}, referred to here as {@code I} in parameter type lists.
+ * <li>The {@code body} handle must not be {@code null}; its type must be of the form
+ * {@code (V I A...)V}, where {@code V} is non-{@code void}, or else {@code (I A...)void}.
+ * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
+ * and we will write {@code (V I A...)V} with the understanding that a {@code void} type {@code V}
+ * is quietly dropped from the parameter list, leaving {@code (I A...)V}.)
+ * <li>The parameter list {@code (V I A...)} of the body contributes to a list
+ * of types called the <em>internal parameter list</em>.
+ * It will constrain the parameter lists of the other loop parts.
+ * <li>As a special case, if the body contributes only {@code V} and {@code I} types,
+ * with no additional {@code A} types, then the internal parameter list is extended by
+ * the argument types {@code A...} of the {@code end} handle.
+ * <li>If the iteration variable types {@code (V I)} are dropped from the internal parameter list, the resulting shorter
+ * list {@code (A...)} is called the <em>external parameter list</em>.
+ * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
+ * additional state variable of the loop.
+ * The body must both accept a leading parameter and return a value of this type {@code V}.
+ * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
+ * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
+ * <a href="MethodHandles.html#effid">effectively identical</a>
+ * to the external parameter list {@code (A...)}.
+ * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
+ * {@linkplain #empty default value}.
+ * <li>The parameter list of {@code start} (of some form {@code (A*)}) must be
+ * effectively identical to the external parameter list {@code (A...)}.
+ * <li>Likewise, the parameter list of {@code end} must be effectively identical
+ * to the external parameter list.
+ * </ul>
+ * <p>
+ * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
+ * <li>The loop handle's result type is the result type {@code V} of the body.
+ * <li>The loop handle's parameter types are the types {@code (A...)},
+ * from the external parameter list.
+ * </ul>
+ * <p>
+ * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
+ * the second loop variable as well as the result type of the loop; and {@code A...}/{@code a...} represent
+ * arguments passed to the loop.
+ * <blockquote><pre>{@code
+ * int start(A...);
+ * int end(A...);
+ * V init(A...);
+ * V body(V, int, A...);
+ * V countedLoop(A... a...) {
+ * int e = end(a...);
+ * int s = start(a...);
+ * V v = init(a...);
+ * for (int i = s; i < e; ++i) {
+ * v = body(v, i, a...);
+ * }
+ * return v;
+ * }
+ * }</pre></blockquote>
+ *
+ * @apiNote The implementation of this method can be expressed as follows:
+ * <blockquote><pre>{@code
+ * MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
+ * MethodHandle returnVar = dropArguments(identity(init.type().returnType()), 0, int.class, int.class);
+ * // assume MH_increment and MH_predicate are handles to implementation-internal methods with
+ * // the following semantics:
+ * // MH_increment: (int limit, int counter) -> counter + 1
+ * // MH_predicate: (int limit, int counter) -> counter < limit
+ * Class<?> counterType = start.type().returnType(); // int
+ * Class<?> returnType = body.type().returnType();
+ * MethodHandle incr = MH_increment, pred = MH_predicate, retv = null;
+ * if (returnType != void.class) { // ignore the V variable
+ * incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
+ * pred = dropArguments(pred, 1, returnType); // ditto
+ * retv = dropArguments(identity(returnType), 0, counterType); // ignore limit
+ * }
+ * body = dropArguments(body, 0, counterType); // ignore the limit variable
+ * MethodHandle[]
+ * loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
+ * bodyClause = { init, body }, // v = init(); v = body(v, i)
+ * indexVar = { start, incr }; // i = start(); i = i + 1
+ * return loop(loopLimit, bodyClause, indexVar);
+ * }
+ * }</pre></blockquote>
+ *
+ * @param start a non-{@code null} handle to return the start value of the loop counter, which must be {@code int}.
+ * See above for other constraints.
+ * @param end a non-{@code null} handle to return the end value of the loop counter (the loop will run to
+ * {@code end-1}). The result type must be {@code int}. See above for other constraints.
+ * @param init optional initializer, providing the initial value of the loop variable.
+ * May be {@code null}, implying a default initial value. See above for other constraints.
+ * @param body body of the loop, which may not be {@code null}.
+ * It controls the loop parameters and result type in the standard case (see above for details).
+ * It must accept its own return type (if non-void) plus an {@code int} parameter (for the counter),
+ * and may accept any number of additional types.
+ * See above for other constraints.
+ *
+ * @return a method handle representing the loop.
+ * @throws NullPointerException if any of the {@code start}, {@code end}, or {@code body} handles is {@code null}.
+ * @throws IllegalArgumentException if any argument violates the rules formulated above.
+ *
+ * @see #countedLoop(MethodHandle, MethodHandle, MethodHandle)
+ * @since 9
+ */
+ public static MethodHandle countedLoop(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
+ countedLoopChecks(start, end, init, body);
+ Class<?> counterType = start.type().returnType(); // int, but who's counting?
+ Class<?> limitType = end.type().returnType(); // yes, int again
+ Class<?> returnType = body.type().returnType();
+ // Android-changed: getConstantHandle is in MethodHandles.
+ // MethodHandle incr = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopStep);
+ // MethodHandle pred = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_countedLoopPred);
+ MethodHandle incr = getConstantHandle(MH_countedLoopStep);
+ MethodHandle pred = getConstantHandle(MH_countedLoopPred);
+ MethodHandle retv = null;
+ if (returnType != void.class) {
+ incr = dropArguments(incr, 1, returnType); // (limit, v, i) => (limit, i)
+ pred = dropArguments(pred, 1, returnType); // ditto
+ retv = dropArguments(identity(returnType), 0, counterType);
+ }
+ body = dropArguments(body, 0, counterType); // ignore the limit variable
+ MethodHandle[]
+ loopLimit = { end, null, pred, retv }, // limit = end(); i < limit || return v
+ bodyClause = { init, body }, // v = init(); v = body(v, i)
+ indexVar = { start, incr }; // i = start(); i = i + 1
+ return loop(loopLimit, bodyClause, indexVar);
+ }
+
+ private static void countedLoopChecks(MethodHandle start, MethodHandle end, MethodHandle init, MethodHandle body) {
+ Objects.requireNonNull(start);
+ Objects.requireNonNull(end);
+ Objects.requireNonNull(body);
+ Class<?> counterType = start.type().returnType();
+ if (counterType != int.class) {
+ MethodType expected = start.type().changeReturnType(int.class);
+ throw misMatchedTypes("start function", start.type(), expected);
+ } else if (end.type().returnType() != counterType) {
+ MethodType expected = end.type().changeReturnType(counterType);
+ throw misMatchedTypes("end function", end.type(), expected);
+ }
+ MethodType bodyType = body.type();
+ Class<?> returnType = bodyType.returnType();
+ List<Class<?>> innerList = bodyType.parameterList();
+ // strip leading V value if present
+ int vsize = (returnType == void.class ? 0 : 1);
+ if (vsize != 0 && (innerList.size() == 0 || innerList.get(0) != returnType)) {
+ // argument list has no "V" => error
+ MethodType expected = bodyType.insertParameterTypes(0, returnType);
+ throw misMatchedTypes("body function", bodyType, expected);
+ } else if (innerList.size() <= vsize || innerList.get(vsize) != counterType) {
+ // missing I type => error
+ MethodType expected = bodyType.insertParameterTypes(vsize, counterType);
+ throw misMatchedTypes("body function", bodyType, expected);
+ }
+ List<Class<?>> outerList = innerList.subList(vsize + 1, innerList.size());
+ if (outerList.isEmpty()) {
+ // special case; take lists from end handle
+ outerList = end.type().parameterList();
+ innerList = bodyType.insertParameterTypes(vsize + 1, outerList).parameterList();
+ }
+ MethodType expected = methodType(counterType, outerList);
+ if (!start.type().effectivelyIdenticalParameters(0, outerList)) {
+ throw misMatchedTypes("start parameter types", start.type(), expected);
+ }
+ if (end.type() != start.type() &&
+ !end.type().effectivelyIdenticalParameters(0, outerList)) {
+ throw misMatchedTypes("end parameter types", end.type(), expected);
+ }
+ if (init != null) {
+ MethodType initType = init.type();
+ if (initType.returnType() != returnType ||
+ !initType.effectivelyIdenticalParameters(0, outerList)) {
+ throw misMatchedTypes("loop initializer", initType, methodType(returnType, outerList));
+ }
+ }
+ }
+
+ /**
+ * Constructs a loop that ranges over the values produced by an {@code Iterator<T>}.
+ * This is a convenience wrapper for the {@linkplain #loop(MethodHandle[][]) generic loop combinator}.
+ * <p>
+ * The iterator itself will be determined by the evaluation of the {@code iterator} handle.
+ * Each value it produces will be stored in a loop iteration variable of type {@code T}.
+ * <p>
+ * If the {@code body} handle returns a non-{@code void} type {@code V}, a leading loop iteration variable
+ * of that type is also present. This variable is initialized using the optional {@code init} handle,
+ * or to the {@linkplain #empty default value} of type {@code V} if that handle is {@code null}.
+ * <p>
+ * In each iteration, the iteration variables are passed to an invocation of the {@code body} handle.
+ * A non-{@code void} value returned from the body (of type {@code V}) updates the leading
+ * iteration variable.
+ * The result of the loop handle execution will be the final {@code V} value of that variable
+ * (or {@code void} if there is no {@code V} variable).
+ * <p>
+ * The following rules hold for the argument handles:<ul>
+ * <li>The {@code body} handle must not be {@code null}; its type must be of the form
+ * {@code (V T A...)V}, where {@code V} is non-{@code void}, or else {@code (T A...)void}.
+ * (In the {@code void} case, we assign the type {@code void} to the name {@code V},
+ * and we will write {@code (V T A...)V} with the understanding that a {@code void} type {@code V}
+ * is quietly dropped from the parameter list, leaving {@code (T A...)V}.)
+ * <li>The parameter list {@code (V T A...)} of the body contributes to a list
+ * of types called the <em>internal parameter list</em>.
+ * It will constrain the parameter lists of the other loop parts.
+ * <li>As a special case, if the body contributes only {@code V} and {@code T} types,
+ * with no additional {@code A} types, then the internal parameter list is extended by
+ * the argument types {@code A...} of the {@code iterator} handle; if it is {@code null} the
+ * single type {@code Iterable} is added and constitutes the {@code A...} list.
+ * <li>If the iteration variable types {@code (V T)} are dropped from the internal parameter list, the resulting shorter
+ * list {@code (A...)} is called the <em>external parameter list</em>.
+ * <li>The body return type {@code V}, if non-{@code void}, determines the type of an
+ * additional state variable of the loop.
+ * The body must both accept a leading parameter and return a value of this type {@code V}.
+ * <li>If {@code init} is non-{@code null}, it must have return type {@code V}.
+ * Its parameter list (of some <a href="MethodHandles.html#astar">form {@code (A*)}</a>) must be
+ * <a href="MethodHandles.html#effid">effectively identical</a>
+ * to the external parameter list {@code (A...)}.
+ * <li>If {@code init} is {@code null}, the loop variable will be initialized to its
+ * {@linkplain #empty default value}.
+ * <li>If the {@code iterator} handle is non-{@code null}, it must have the return
+ * type {@code java.util.Iterator} or a subtype thereof.
+ * The iterator it produces when the loop is executed will be assumed
+ * to yield values which can be converted to type {@code T}.
+ * <li>The parameter list of an {@code iterator} that is non-{@code null} (of some form {@code (A*)}) must be
+ * effectively identical to the external parameter list {@code (A...)}.
+ * <li>If {@code iterator} is {@code null} it defaults to a method handle which behaves
+ * like {@link java.lang.Iterable#iterator()}. In that case, the internal parameter list
+ * {@code (V T A...)} must have at least one {@code A} type, and the default iterator
+ * handle parameter is adjusted to accept the leading {@code A} type, as if by
+ * the {@link MethodHandle#asType asType} conversion method.
+ * The leading {@code A} type must be {@code Iterable} or a subtype thereof.
+ * This conversion step, done at loop construction time, must not throw a {@code WrongMethodTypeException}.
+ * </ul>
+ * <p>
+ * The type {@code T} may be either a primitive or reference.
+ * Since type {@code Iterator<T>} is erased in the method handle representation to the raw type {@code Iterator},
+ * the {@code iteratedLoop} combinator adjusts the leading argument type for {@code body} to {@code Object}
+ * as if by the {@link MethodHandle#asType asType} conversion method.
+ * Therefore, if an iterator of the wrong type appears as the loop is executed, runtime exceptions may occur
+ * as the result of dynamic conversions performed by {@link MethodHandle#asType(MethodType)}.
+ * <p>
+ * The resulting loop handle's result type and parameter signature are determined as follows:<ul>
+ * <li>The loop handle's result type is the result type {@code V} of the body.
+ * <li>The loop handle's parameter types are the types {@code (A...)},
+ * from the external parameter list.
+ * </ul>
+ * <p>
+ * Here is pseudocode for the resulting loop handle. In the code, {@code V}/{@code v} represent the type / value of
+ * the loop variable as well as the result type of the loop; {@code T}/{@code t}, that of the elements of the
+ * structure the loop iterates over, and {@code A...}/{@code a...} represent arguments passed to the loop.
+ * <blockquote><pre>{@code
+ * Iterator<T> iterator(A...); // defaults to Iterable::iterator
+ * V init(A...);
+ * V body(V,T,A...);
+ * V iteratedLoop(A... a...) {
+ * Iterator<T> it = iterator(a...);
+ * V v = init(a...);
+ * while (it.hasNext()) {
+ * T t = it.next();
+ * v = body(v, t, a...);
+ * }
+ * return v;
+ * }
+ * }</pre></blockquote>
+ *
+ * @apiNote Example:
+ * <blockquote><pre>{@code
+ * // get an iterator from a list
+ * static List<String> reverseStep(List<String> r, String e) {
+ * r.add(0, e);
+ * return r;
+ * }
+ * static List<String> newArrayList() { return new ArrayList<>(); }
+ * // assume MH_reverseStep and MH_newArrayList are handles to the above methods
+ * MethodHandle loop = MethodHandles.iteratedLoop(null, MH_newArrayList, MH_reverseStep);
+ * List<String> list = Arrays.asList("a", "b", "c", "d", "e");
+ * List<String> reversedList = Arrays.asList("e", "d", "c", "b", "a");
+ * assertEquals(reversedList, (List<String>) loop.invoke(list));
+ * }</pre></blockquote>
+ *
+ * @apiNote The implementation of this method can be expressed approximately as follows:
+ * <blockquote><pre>{@code
+ * MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
+ * // assume MH_next, MH_hasNext, MH_startIter are handles to methods of Iterator/Iterable
+ * Class<?> returnType = body.type().returnType();
+ * Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
+ * MethodHandle nextVal = MH_next.asType(MH_next.type().changeReturnType(ttype));
+ * MethodHandle retv = null, step = body, startIter = iterator;
+ * if (returnType != void.class) {
+ * // the simple thing first: in (I V A...), drop the I to get V
+ * retv = dropArguments(identity(returnType), 0, Iterator.class);
+ * // body type signature (V T A...), internal loop types (I V A...)
+ * step = swapArguments(body, 0, 1); // swap V <-> T
+ * }
+ * if (startIter == null) startIter = MH_getIter;
+ * MethodHandle[]
+ * iterVar = { startIter, null, MH_hasNext, retv }, // it = iterator; while (it.hasNext())
+ * bodyClause = { init, filterArguments(step, 0, nextVal) }; // v = body(v, t, a)
+ * return loop(iterVar, bodyClause);
+ * }
+ * }</pre></blockquote>
+ *
+ * @param iterator an optional handle to return the iterator to start the loop.
+ * If non-{@code null}, the handle must return {@link java.util.Iterator} or a subtype.
+ * See above for other constraints.
+ * @param init optional initializer, providing the initial value of the loop variable.
+ * May be {@code null}, implying a default initial value. See above for other constraints.
+ * @param body body of the loop, which may not be {@code null}.
+ * It controls the loop parameters and result type in the standard case (see above for details).
+ * It must accept its own return type (if non-void) plus a {@code T} parameter (for the iterated values),
+ * and may accept any number of additional types.
+ * See above for other constraints.
+ *
+ * @return a method handle embodying the iteration loop functionality.
+ * @throws NullPointerException if the {@code body} handle is {@code null}.
+ * @throws IllegalArgumentException if any argument violates the above requirements.
+ *
+ * @since 9
+ */
+ public static MethodHandle iteratedLoop(MethodHandle iterator, MethodHandle init, MethodHandle body) {
+ Class<?> iterableType = iteratedLoopChecks(iterator, init, body);
+ Class<?> returnType = body.type().returnType();
+ // Android-changed: getConstantHandle is in MethodHandles.
+ // MethodHandle hasNext = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iteratePred);
+ // MethodHandle nextRaw = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_iterateNext);
+ MethodHandle hasNext = getConstantHandle(MH_iteratePred);
+ MethodHandle nextRaw = getConstantHandle(MH_iterateNext);
+ MethodHandle startIter;
+ MethodHandle nextVal;
+ {
+ MethodType iteratorType;
+ if (iterator == null) {
+ // derive argument type from body, if available, else use Iterable
+ // Android-changed: getConstantHandle is in MethodHandles.
+ // startIter = MethodHandleImpl.getConstantHandle(MethodHandleImpl.MH_initIterator);
+ startIter = getConstantHandle(MH_initIterator);
+ iteratorType = startIter.type().changeParameterType(0, iterableType);
+ } else {
+ // force return type to the internal iterator class
+ iteratorType = iterator.type().changeReturnType(Iterator.class);
+ startIter = iterator;
+ }
+ Class<?> ttype = body.type().parameterType(returnType == void.class ? 0 : 1);
+ MethodType nextValType = nextRaw.type().changeReturnType(ttype);
+
+ // perform the asType transforms under an exception transformer, as per spec.:
+ try {
+ startIter = startIter.asType(iteratorType);
+ nextVal = nextRaw.asType(nextValType);
+ } catch (WrongMethodTypeException ex) {
+ throw new IllegalArgumentException(ex);
+ }
+ }
+
+ MethodHandle retv = null, step = body;
+ if (returnType != void.class) {
+ // the simple thing first: in (I V A...), drop the I to get V
+ retv = dropArguments(identity(returnType), 0, Iterator.class);
+ // body type signature (V T A...), internal loop types (I V A...)
+ step = swapArguments(body, 0, 1); // swap V <-> T
+ }
+
+ MethodHandle[]
+ iterVar = { startIter, null, hasNext, retv },
+ bodyClause = { init, filterArgument(step, 0, nextVal) };
+ return loop(iterVar, bodyClause);
+ }
+
+ private static Class<?> iteratedLoopChecks(MethodHandle iterator, MethodHandle init, MethodHandle body) {
+ Objects.requireNonNull(body);
+ MethodType bodyType = body.type();
+ Class<?> returnType = bodyType.returnType();
+ List<Class<?>> internalParamList = bodyType.parameterList();
+ // strip leading V value if present
+ int vsize = (returnType == void.class ? 0 : 1);
+ if (vsize != 0 && (internalParamList.size() == 0 || internalParamList.get(0) != returnType)) {
+ // argument list has no "V" => error
+ MethodType expected = bodyType.insertParameterTypes(0, returnType);
+ throw misMatchedTypes("body function", bodyType, expected);
+ } else if (internalParamList.size() <= vsize) {
+ // missing T type => error
+ MethodType expected = bodyType.insertParameterTypes(vsize, Object.class);
+ throw misMatchedTypes("body function", bodyType, expected);
+ }
+ List<Class<?>> externalParamList = internalParamList.subList(vsize + 1, internalParamList.size());
+ Class<?> iterableType = null;
+ if (iterator != null) {
+ // special case; if the body handle only declares V and T then
+ // the external parameter list is obtained from iterator handle
+ if (externalParamList.isEmpty()) {
+ externalParamList = iterator.type().parameterList();
+ }
+ MethodType itype = iterator.type();
+ if (!Iterator.class.isAssignableFrom(itype.returnType())) {
+ throw newIllegalArgumentException("iteratedLoop first argument must have Iterator return type");
+ }
+ if (!itype.effectivelyIdenticalParameters(0, externalParamList)) {
+ MethodType expected = methodType(itype.returnType(), externalParamList);
+ throw misMatchedTypes("iterator parameters", itype, expected);
+ }
+ } else {
+ if (externalParamList.isEmpty()) {
+ // special case; if the iterator handle is null and the body handle
+ // only declares V and T then the external parameter list consists
+ // of Iterable
+ externalParamList = Arrays.asList(Iterable.class);
+ iterableType = Iterable.class;
+ } else {
+ // special case; if the iterator handle is null and the external
+ // parameter list is not empty then the first parameter must be
+ // assignable to Iterable
+ iterableType = externalParamList.get(0);
+ if (!Iterable.class.isAssignableFrom(iterableType)) {
+ throw newIllegalArgumentException(
+ "inferred first loop argument must inherit from Iterable: " + iterableType);
+ }
+ }
+ }
+ if (init != null) {
+ MethodType initType = init.type();
+ if (initType.returnType() != returnType ||
+ !initType.effectivelyIdenticalParameters(0, externalParamList)) {
+ throw misMatchedTypes("loop initializer", initType, methodType(returnType, externalParamList));
+ }
+ }
+ return iterableType; // help the caller a bit
+ }
+
+ /*non-public*/ static MethodHandle swapArguments(MethodHandle mh, int i, int j) {
+ // there should be a better way to uncross my wires
+ int arity = mh.type().parameterCount();
+ int[] order = new int[arity];
+ for (int k = 0; k < arity; k++) order[k] = k;
+ order[i] = j; order[j] = i;
+ Class<?>[] types = mh.type().parameterArray();
+ Class<?> ti = types[i]; types[i] = types[j]; types[j] = ti;
+ MethodType swapType = methodType(mh.type().returnType(), types);
+ return permuteArguments(mh, swapType, order);
+ }
+
+ /**
+ * Makes a method handle that adapts a {@code target} method handle by wrapping it in a {@code try-finally} block.
+ * Another method handle, {@code cleanup}, represents the functionality of the {@code finally} block. Any exception
+ * thrown during the execution of the {@code target} handle will be passed to the {@code cleanup} handle. The
+ * exception will be rethrown, unless {@code cleanup} handle throws an exception first. The
+ * value returned from the {@code cleanup} handle's execution will be the result of the execution of the
+ * {@code try-finally} handle.
+ * <p>
+ * The {@code cleanup} handle will be passed one or two additional leading arguments.
+ * The first is the exception thrown during the
+ * execution of the {@code target} handle, or {@code null} if no exception was thrown.
+ * The second is the result of the execution of the {@code target} handle, or, if it throws an exception,
+ * a {@code null}, zero, or {@code false} value of the required type is supplied as a placeholder.
+ * The second argument is not present if the {@code target} handle has a {@code void} return type.
+ * (Note that, except for argument type conversions, combinators represent {@code void} values in parameter lists
+ * by omitting the corresponding paradoxical arguments, not by inserting {@code null} or zero values.)
+ * <p>
+ * The {@code target} and {@code cleanup} handles must have the same corresponding argument and return types, except
+ * that the {@code cleanup} handle may omit trailing arguments. Also, the {@code cleanup} handle must have one or
+ * two extra leading parameters:<ul>
+ * <li>a {@code Throwable}, which will carry the exception thrown by the {@code target} handle (if any); and
+ * <li>a parameter of the same type as the return type of both {@code target} and {@code cleanup}, which will carry
+ * the result from the execution of the {@code target} handle.
+ * This parameter is not present if the {@code target} returns {@code void}.
+ * </ul>
+ * <p>
+ * The pseudocode for the resulting adapter looks as follows. In the code, {@code V} represents the result type of
+ * the {@code try/finally} construct; {@code A}/{@code a}, the types and values of arguments to the resulting
+ * handle consumed by the cleanup; and {@code B}/{@code b}, those of arguments to the resulting handle discarded by
+ * the cleanup.
+ * <blockquote><pre>{@code
+ * V target(A..., B...);
+ * V cleanup(Throwable, V, A...);
+ * V adapter(A... a, B... b) {
+ * V result = (zero value for V);
+ * Throwable throwable = null;
+ * try {
+ * result = target(a..., b...);
+ * } catch (Throwable t) {
+ * throwable = t;
+ * throw t;
+ * } finally {
+ * result = cleanup(throwable, result, a...);
+ * }
+ * return result;
+ * }
+ * }</pre></blockquote>
+ * <p>
+ * Note that the saved arguments ({@code a...} in the pseudocode) cannot
+ * be modified by execution of the target, and so are passed unchanged
+ * from the caller to the cleanup, if it is invoked.
+ * <p>
+ * The target and cleanup must return the same type, even if the cleanup
+ * always throws.
+ * To create such a throwing cleanup, compose the cleanup logic
+ * with {@link #throwException throwException},
+ * in order to create a method handle of the correct return type.
+ * <p>
+ * Note that {@code tryFinally} never converts exceptions into normal returns.
+ * In rare cases where exceptions must be converted in that way, first wrap
+ * the target with {@link #catchException(MethodHandle, Class, MethodHandle)}
+ * to capture an outgoing exception, and then wrap with {@code tryFinally}.
+ * <p>
+ * It is recommended that the first parameter type of {@code cleanup} be
+ * declared {@code Throwable} rather than a narrower subtype. This ensures
+ * {@code cleanup} will always be invoked with whatever exception that
+ * {@code target} throws. Declaring a narrower type may result in a
+ * {@code ClassCastException} being thrown by the {@code try-finally}
+ * handle if the type of the exception thrown by {@code target} is not
+ * assignable to the first parameter type of {@code cleanup}. Note that
+ * various exception types of {@code VirtualMachineError},
+ * {@code LinkageError}, and {@code RuntimeException} can in principle be
+ * thrown by almost any kind of Java code, and a finally clause that
+ * catches (say) only {@code IOException} would mask any of the others
+ * behind a {@code ClassCastException}.
+ *
+ * @param target the handle whose execution is to be wrapped in a {@code try} block.
+ * @param cleanup the handle that is invoked in the finally block.
+ *
+ * @return a method handle embodying the {@code try-finally} block composed of the two arguments.
+ * @throws NullPointerException if any argument is null
+ * @throws IllegalArgumentException if {@code cleanup} does not accept
+ * the required leading arguments, or if the method handle types do
+ * not match in their return types and their
+ * corresponding trailing parameters
+ *
+ * @see MethodHandles#catchException(MethodHandle, Class, MethodHandle)
+ * @since 9
+ */
+ public static MethodHandle tryFinally(MethodHandle target, MethodHandle cleanup) {
+ List<Class<?>> targetParamTypes = target.type().parameterList();
+ Class<?> rtype = target.type().returnType();
+
+ tryFinallyChecks(target, cleanup);
+
+ // Match parameter lists: if the cleanup has a shorter parameter list than the target, add ignored arguments.
+ // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
+ // target parameter list.
+ cleanup = dropArgumentsToMatch(cleanup, (rtype == void.class ? 1 : 2), targetParamTypes, 0);
+
+ // Ensure that the intrinsic type checks the instance thrown by the
+ // target against the first parameter of cleanup
+ cleanup = cleanup.asType(cleanup.type().changeParameterType(0, Throwable.class));
+
+ // Use asFixedArity() to avoid unnecessary boxing of last argument for VarargsCollector case.
+ // Android-changed: use Transformer implementation.
+ // return MethodHandleImpl.makeTryFinally(target.asFixedArity(), cleanup.asFixedArity(), rtype, targetParamTypes);
+ return new Transformers.TryFinally(target.asFixedArity(), cleanup.asFixedArity());
+ }
+
+ private static void tryFinallyChecks(MethodHandle target, MethodHandle cleanup) {
+ Class<?> rtype = target.type().returnType();
+ if (rtype != cleanup.type().returnType()) {
+ throw misMatchedTypes("target and return types", cleanup.type().returnType(), rtype);
+ }
+ MethodType cleanupType = cleanup.type();
+ if (!Throwable.class.isAssignableFrom(cleanupType.parameterType(0))) {
+ throw misMatchedTypes("cleanup first argument and Throwable", cleanup.type(), Throwable.class);
+ }
+ if (rtype != void.class && cleanupType.parameterType(1) != rtype) {
+ throw misMatchedTypes("cleanup second argument and target return type", cleanup.type(), rtype);
+ }
+ // The cleanup parameter list (minus the leading Throwable and result parameters) must be a sublist of the
+ // target parameter list.
+ int cleanupArgIndex = rtype == void.class ? 1 : 2;
+ if (!cleanupType.effectivelyIdenticalParameters(cleanupArgIndex, target.type().parameterList())) {
+ throw misMatchedTypes("cleanup parameters after (Throwable,result) and target parameter list prefix",
+ cleanup.type(), target.type());
+ }
+ }
+
+ /**
+ * Creates a table switch method handle, which can be used to switch over a set of target
+ * method handles, based on a given target index, called selector.
+ * <p>
+ * For a selector value of {@code n}, where {@code n} falls in the range {@code [0, N)},
+ * and where {@code N} is the number of target method handles, the table switch method
+ * handle will invoke the n-th target method handle from the list of target method handles.
+ * <p>
+ * For a selector value that does not fall in the range {@code [0, N)}, the table switch
+ * method handle will invoke the given fallback method handle.
+ * <p>
+ * All method handles passed to this method must have the same type, with the additional
+ * requirement that the leading parameter be of type {@code int}. The leading parameter
+ * represents the selector.
+ * <p>
+ * Any trailing parameters present in the type will appear on the returned table switch
+ * method handle as well. Any arguments assigned to these parameters will be forwarded,
+ * together with the selector value, to the selected method handle when invoking it.
+ *
+ * @apiNote Example:
+ * The cases each drop the {@code selector} value they are given, and take an additional
+ * {@code String} argument, which is concatenated (using {@link String#concat(String)})
+ * to a specific constant label string for each case:
+ * <blockquote><pre>{@code
+ * MethodHandles.Lookup lookup = MethodHandles.lookup();
+ * MethodHandle caseMh = lookup.findVirtual(String.class, "concat",
+ * MethodType.methodType(String.class, String.class));
+ * caseMh = MethodHandles.dropArguments(caseMh, 0, int.class);
+ *
+ * MethodHandle caseDefault = MethodHandles.insertArguments(caseMh, 1, "default: ");
+ * MethodHandle case0 = MethodHandles.insertArguments(caseMh, 1, "case 0: ");
+ * MethodHandle case1 = MethodHandles.insertArguments(caseMh, 1, "case 1: ");
+ *
+ * MethodHandle mhSwitch = MethodHandles.tableSwitch(
+ * caseDefault,
+ * case0,
+ * case1
+ * );
+ *
+ * assertEquals("default: data", (String) mhSwitch.invokeExact(-1, "data"));
+ * assertEquals("case 0: data", (String) mhSwitch.invokeExact(0, "data"));
+ * assertEquals("case 1: data", (String) mhSwitch.invokeExact(1, "data"));
+ * assertEquals("default: data", (String) mhSwitch.invokeExact(2, "data"));
+ * }</pre></blockquote>
+ *
+ * @param fallback the fallback method handle that is called when the selector is not
+ * within the range {@code [0, N)}.
+ * @param targets array of target method handles.
+ * @return the table switch method handle.
+ * @throws NullPointerException if {@code fallback}, the {@code targets} array, or any
+ * any of the elements of the {@code targets} array are
+ * {@code null}.
+ * @throws IllegalArgumentException if the {@code targets} array is empty, if the leading
+ * parameter of the fallback handle or any of the target
+ * handles is not {@code int}, or if the types of
+ * the fallback handle and all of target handles are
+ * not the same.
+ */
+ public static MethodHandle tableSwitch(MethodHandle fallback, MethodHandle... targets) {
+ Objects.requireNonNull(fallback);
+ Objects.requireNonNull(targets);
+ targets = targets.clone();
+ MethodType type = tableSwitchChecks(fallback, targets);
+ // Android-changed: use a Transformer for the implementation.
+ // return MethodHandleImpl.makeTableSwitch(type, fallback, targets);
+ return new Transformers.TableSwitch(type, fallback, targets);
+ }
+
+ private static MethodType tableSwitchChecks(MethodHandle defaultCase, MethodHandle[] caseActions) {
+ if (caseActions.length == 0)
+ throw new IllegalArgumentException("Not enough cases: " + Arrays.toString(caseActions));
+
+ MethodType expectedType = defaultCase.type();
+
+ if (!(expectedType.parameterCount() >= 1) || expectedType.parameterType(0) != int.class)
+ throw new IllegalArgumentException(
+ "Case actions must have int as leading parameter: " + Arrays.toString(caseActions));
+
+ for (MethodHandle mh : caseActions) {
+ Objects.requireNonNull(mh);
+ // Android-changed: MethodType's not interned.
+ // if (mh.type() != expectedType)
+ if (!mh.type().equals(expectedType))
+ throw new IllegalArgumentException(
+ "Case actions must have the same type: " + Arrays.toString(caseActions));
+ }
+
+ return expectedType;
+ }
+
+ // BEGIN Android-added: Code from OpenJDK's MethodHandleImpl.
+
+ /**
+ * This method is bound as the predicate in {@linkplain MethodHandles#countedLoop(MethodHandle, MethodHandle,
+ * MethodHandle) counting loops}.
+ *
+ * @param limit the upper bound of the parameter, statically bound at loop creation time.
+ * @param counter the counter parameter, passed in during loop execution.
+ *
+ * @return whether the counter has reached the limit.
+ * @hide
+ */
+ public static boolean countedLoopPredicate(int limit, int counter) {
+ return counter < limit;
+ }
+
+ /**
+ * This method is bound as the step function in {@linkplain MethodHandles#countedLoop(MethodHandle, MethodHandle,
+ * MethodHandle) counting loops} to increment the counter.
+ *
+ * @param limit the upper bound of the loop counter (ignored).
+ * @param counter the loop counter.
+ *
+ * @return the loop counter incremented by 1.
+ * @hide
+ */
+ public static int countedLoopStep(int limit, int counter) {
+ return counter + 1;
+ }
+
+ /**
+ * This is bound to initialize the loop-local iterator in {@linkplain MethodHandles#iteratedLoop iterating loops}.
+ *
+ * @param it the {@link Iterable} over which the loop iterates.
+ *
+ * @return an {@link Iterator} over the argument's elements.
+ * @hide
+ */
+ public static Iterator<?> initIterator(Iterable<?> it) {
+ return it.iterator();
+ }
+
+ /**
+ * This method is bound as the predicate in {@linkplain MethodHandles#iteratedLoop iterating loops}.
+ *
+ * @param it the iterator to be checked.
+ *
+ * @return {@code true} iff there are more elements to iterate over.
+ * @hide
+ */
+ public static boolean iteratePredicate(Iterator<?> it) {
+ return it.hasNext();
+ }
+
+ /**
+ * This method is bound as the step for retrieving the current value from the iterator in {@linkplain
+ * MethodHandles#iteratedLoop iterating loops}.
+ *
+ * @param it the iterator.
+ *
+ * @return the next element from the iterator.
+ * @hide
+ */
+ public static Object iterateNext(Iterator<?> it) {
+ return it.next();
+ }
+
+ // Indexes into constant method handles:
+ static final int
+ MH_cast = 0,
+ MH_selectAlternative = 1,
+ MH_copyAsPrimitiveArray = 2,
+ MH_fillNewTypedArray = 3,
+ MH_fillNewArray = 4,
+ MH_arrayIdentity = 5,
+ MH_countedLoopPred = 6,
+ MH_countedLoopStep = 7,
+ MH_initIterator = 8,
+ MH_iteratePred = 9,
+ MH_iterateNext = 10,
+ MH_Array_newInstance = 11,
+ MH_LIMIT = 12;
+
+ static MethodHandle getConstantHandle(int idx) {
+ MethodHandle handle = HANDLES[idx];
+ if (handle != null) {
+ return handle;
+ }
+ return setCachedHandle(idx, makeConstantHandle(idx));
+ }
+
+ private static synchronized MethodHandle setCachedHandle(int idx, final MethodHandle method) {
+ // Simulate a CAS, to avoid racy duplication of results.
+ MethodHandle prev = HANDLES[idx];
+ if (prev != null) {
+ return prev;
+ }
+ HANDLES[idx] = method;
+ return method;
+ }
+
+ // Local constant method handles:
+ private static final @Stable MethodHandle[] HANDLES = new MethodHandle[MH_LIMIT];
+
+ private static MethodHandle makeConstantHandle(int idx) {
+ try {
+ // Android-added: local IMPL_LOOKUP.
+ final Lookup IMPL_LOOKUP = MethodHandles.Lookup.IMPL_LOOKUP;
+ switch (idx) {
+ // Android-removed: not-used.
+ /*
+ case MH_cast:
+ return IMPL_LOOKUP.findVirtual(Class.class, "cast",
+ MethodType.methodType(Object.class, Object.class));
+ case MH_copyAsPrimitiveArray:
+ return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "copyAsPrimitiveArray",
+ MethodType.methodType(Object.class, Wrapper.class, Object[].class));
+ case MH_arrayIdentity:
+ return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "identity",
+ MethodType.methodType(Object[].class, Object[].class));
+ case MH_fillNewArray:
+ return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "fillNewArray",
+ MethodType.methodType(Object[].class, Integer.class, Object[].class));
+ case MH_fillNewTypedArray:
+ return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "fillNewTypedArray",
+ MethodType.methodType(Object[].class, Object[].class, Integer.class, Object[].class));
+ case MH_selectAlternative:
+ return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "selectAlternative",
+ MethodType.methodType(MethodHandle.class, boolean.class, MethodHandle.class, MethodHandle.class));
+ */
+ case MH_countedLoopPred:
+ // Android-changed: methods moved to this file.
+ // return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "countedLoopPredicate",
+ // MethodType.methodType(boolean.class, int.class, int.class));
+ return IMPL_LOOKUP.findStatic(MethodHandles.class, "countedLoopPredicate",
+ MethodType.methodType(boolean.class, int.class, int.class));
+ case MH_countedLoopStep:
+ // Android-changed: methods moved to this file.
+ // return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "countedLoopStep",
+ // MethodType.methodType(int.class, int.class, int.class));
+ return IMPL_LOOKUP.findStatic(MethodHandles.class, "countedLoopStep",
+ MethodType.methodType(int.class, int.class, int.class));
+ case MH_initIterator:
+ // Android-changed: methods moved to this file.
+ // return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "initIterator",
+ // MethodType.methodType(Iterator.class, Iterable.class));
+ return IMPL_LOOKUP.findStatic(MethodHandles.class, "initIterator",
+ MethodType.methodType(Iterator.class, Iterable.class));
+ case MH_iteratePred:
+ // Android-changed: methods moved to this file.
+ // return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "iteratePredicate",
+ // MethodType.methodType(boolean.class, Iterator.class));
+ return IMPL_LOOKUP.findStatic(MethodHandles.class, "iteratePredicate",
+ MethodType.methodType(boolean.class, Iterator.class));
+ case MH_iterateNext:
+ // Android-changed: methods moved to this file.
+ // return IMPL_LOOKUP.findStatic(MethodHandleImpl.class, "iterateNext",
+ // MethodType.methodType(Object.class, Iterator.class));
+ return IMPL_LOOKUP.findStatic(MethodHandles.class, "iterateNext",
+ MethodType.methodType(Object.class, Iterator.class));
+ // Android-removed: not-used.
+ /*
+ case MH_Array_newInstance:
+ return IMPL_LOOKUP.findStatic(Array.class, "newInstance",
+ MethodType.methodType(Object.class, Class.class, int.class));
+ */
+ }
+ } catch (ReflectiveOperationException ex) {
+ throw newInternalError(ex);
+ }
+
+ throw newInternalError("Unknown function index: " + idx);
+ }
+ // END Android-added: Code from OpenJDK's MethodHandleImpl.
+}
