| Rahul Ravikumar | 0533600 | 2019-10-14 15:04:32 -0700 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved. |
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| 4 | * |
| 5 | * This code is free software; you can redistribute it and/or modify it |
| 6 | * under the terms of the GNU General Public License version 2 only, as |
| 7 | * published by the Free Software Foundation. Oracle designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Oracle in the LICENSE file that accompanied this code. |
| 10 | * |
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT |
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 14 | * version 2 for more details (a copy is included in the LICENSE file that |
| 15 | * accompanied this code). |
| 16 | * |
| 17 | * You should have received a copy of the GNU General Public License version |
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, |
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| 20 | * |
| 21 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| 22 | * or visit www.oracle.com if you need additional information or have any |
| 23 | * questions. |
| 24 | */ |
| 25 | |
| 26 | package java.lang; |
| 27 | |
| 28 | import java.lang.annotation.*; |
| 29 | |
| 30 | /** |
| 31 | * An informative annotation type used to indicate that an interface |
| 32 | * type declaration is intended to be a <i>functional interface</i> as |
| 33 | * defined by the Java Language Specification. |
| 34 | * |
| 35 | * Conceptually, a functional interface has exactly one abstract |
| 36 | * method. Since {@linkplain java.lang.reflect.Method#isDefault() |
| 37 | * default methods} have an implementation, they are not abstract. If |
| 38 | * an interface declares an abstract method overriding one of the |
| 39 | * public methods of {@code java.lang.Object}, that also does |
| 40 | * <em>not</em> count toward the interface's abstract method count |
| 41 | * since any implementation of the interface will have an |
| 42 | * implementation from {@code java.lang.Object} or elsewhere. |
| 43 | * |
| 44 | * <p>Note that instances of functional interfaces can be created with |
| 45 | * lambda expressions, method references, or constructor references. |
| 46 | * |
| 47 | * <p>If a type is annotated with this annotation type, compilers are |
| 48 | * required to generate an error message unless: |
| 49 | * |
| 50 | * <ul> |
| 51 | * <li> The type is an interface type and not an annotation type, enum, or class. |
| 52 | * <li> The annotated type satisfies the requirements of a functional interface. |
| 53 | * </ul> |
| 54 | * |
| 55 | * <p>However, the compiler will treat any interface meeting the |
| 56 | * definition of a functional interface as a functional interface |
| 57 | * regardless of whether or not a {@code FunctionalInterface} |
| 58 | * annotation is present on the interface declaration. |
| 59 | * |
| 60 | * @jls 4.3.2. The Class Object |
| 61 | * @jls 9.8 Functional Interfaces |
| 62 | * @jls 9.4.3 Interface Method Body |
| 63 | * @since 1.8 |
| 64 | */ |
| 65 | @Documented |
| 66 | @Retention(RetentionPolicy.RUNTIME) |
| 67 | @Target(ElementType.TYPE) |
| 68 | public @interface FunctionalInterface {} |
