| /* |
| * Copyright (c) 1997, 2021, 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.util; |
| |
| import java.io.Serializable; |
| import java.util.function.Function; |
| import java.util.function.ToIntFunction; |
| import java.util.function.ToLongFunction; |
| import java.util.function.ToDoubleFunction; |
| import java.util.Comparators; |
| |
| /** |
| * A comparison function, which imposes a <i>total ordering</i> on |
| * some collection of objects. Comparators can be passed to a sort |
| * method (such as {@link Collections#sort(List,Comparator) |
| * Collections.sort} or {@link Arrays#sort(Object[],Comparator) |
| * Arrays.sort}) to allow precise control over the sort order. |
| * Comparators can also be used to control the order of certain data |
| * structures (such as {@linkplain SortedSet sorted sets} or |
| * {@linkplain SortedMap sorted maps}), or to provide an ordering for |
| * collections of objects that don't have a {@linkplain Comparable |
| * natural ordering}.<p> |
| * |
| * The ordering imposed by a comparator {@code c} on a set of elements |
| * {@code S} is said to be <i>consistent with equals</i> if and only if |
| * {@code c.compare(e1, e2)==0} has the same boolean value as |
| * {@code e1.equals(e2)} for every {@code e1} and {@code e2} in |
| * {@code S}.<p> |
| * |
| * Caution should be exercised when using a comparator capable of imposing an |
| * ordering inconsistent with equals to order a sorted set (or sorted map). |
| * Suppose a sorted set (or sorted map) with an explicit comparator {@code c} |
| * is used with elements (or keys) drawn from a set {@code S}. If the |
| * ordering imposed by {@code c} on {@code S} is inconsistent with equals, |
| * the sorted set (or sorted map) will behave "strangely." In particular the |
| * sorted set (or sorted map) will violate the general contract for set (or |
| * map), which is defined in terms of {@code equals}.<p> |
| * |
| * For example, suppose one adds two elements {@code a} and {@code b} such that |
| * {@code (a.equals(b) && c.compare(a, b) != 0)} |
| * to an empty {@code TreeSet} with comparator {@code c}. |
| * The second {@code add} operation will return |
| * true (and the size of the tree set will increase) because {@code a} and |
| * {@code b} are not equivalent from the tree set's perspective, even though |
| * this is contrary to the specification of the |
| * {@link Set#add Set.add} method.<p> |
| * |
| * Note: It is generally a good idea for comparators to also implement |
| * {@code java.io.Serializable}, as they may be used as ordering methods in |
| * serializable data structures (like {@link TreeSet}, {@link TreeMap}). In |
| * order for the data structure to serialize successfully, the comparator (if |
| * provided) must implement {@code Serializable}.<p> |
| * |
| * For the mathematically inclined, the <i>relation</i> that defines the |
| * <i>imposed ordering</i> that a given comparator {@code c} imposes on a |
| * given set of objects {@code S} is:<pre> |
| * {(x, y) such that c.compare(x, y) <= 0}. |
| * </pre> The <i>quotient</i> for this total order is:<pre> |
| * {(x, y) such that c.compare(x, y) == 0}. |
| * </pre> |
| * |
| * It follows immediately from the contract for {@code compare} that the |
| * quotient is an <i>equivalence relation</i> on {@code S}, and that the |
| * imposed ordering is a <i>total order</i> on {@code S}. When we say that |
| * the ordering imposed by {@code c} on {@code S} is <i>consistent with |
| * equals</i>, we mean that the quotient for the ordering is the equivalence |
| * relation defined by the objects' {@link Object#equals(Object) |
| * equals(Object)} method(s):<pre> |
| * {(x, y) such that x.equals(y)}. </pre> |
| * |
| * In other words, when the imposed ordering is consistent with |
| * equals, the equivalence classes defined by the equivalence relation |
| * of the {@code equals} method and the equivalence classes defined by |
| * the quotient of the {@code compare} method are the same. |
| |
| * <p>Unlike {@code Comparable}, a comparator may optionally permit |
| * comparison of null arguments, while maintaining the requirements for |
| * an equivalence relation. |
| * |
| * <p>This interface is a member of the |
| * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework"> |
| * Java Collections Framework</a>. |
| * |
| * @param <T> the type of objects that may be compared by this comparator |
| * |
| * @author Josh Bloch |
| * @author Neal Gafter |
| * @see Comparable |
| * @see java.io.Serializable |
| * @since 1.2 |
| */ |
| @FunctionalInterface |
| public interface Comparator<T> { |
| /** |
| * Compares its two arguments for order. Returns a negative integer, |
| * zero, or a positive integer as the first argument is less than, equal |
| * to, or greater than the second.<p> |
| * |
| * The implementor must ensure that {@link Integer#signum |
| * signum}{@code (compare(x, y)) == -signum(compare(y, x))} for |
| * all {@code x} and {@code y}. (This implies that {@code |
| * compare(x, y)} must throw an exception if and only if {@code |
| * compare(y, x)} throws an exception.)<p> |
| * |
| * The implementor must also ensure that the relation is transitive: |
| * {@code ((compare(x, y)>0) && (compare(y, z)>0))} implies |
| * {@code compare(x, z)>0}.<p> |
| * |
| * Finally, the implementor must ensure that {@code compare(x, |
| * y)==0} implies that {@code signum(compare(x, |
| * z))==signum(compare(y, z))} for all {@code z}. |
| * |
| * @apiNote |
| * It is generally the case, but <i>not</i> strictly required that |
| * {@code (compare(x, y)==0) == (x.equals(y))}. Generally speaking, |
| * any comparator that violates this condition should clearly indicate |
| * this fact. The recommended language is "Note: this comparator |
| * imposes orderings that are inconsistent with equals." |
| * |
| * @param o1 the first object to be compared. |
| * @param o2 the second object to be compared. |
| * @return a negative integer, zero, or a positive integer as the |
| * first argument is less than, equal to, or greater than the |
| * second. |
| * @throws NullPointerException if an argument is null and this |
| * comparator does not permit null arguments |
| * @throws ClassCastException if the arguments' types prevent them from |
| * being compared by this comparator. |
| */ |
| int compare(T o1, T o2); |
| |
| /** |
| * Indicates whether some other object is "equal to" |
| * this comparator. This method must obey the general contract of |
| * {@link Object#equals(Object)}. Additionally, this method can |
| * return {@code true} <i>only</i> if the specified object is also |
| * a comparator and it imposes the same ordering as this |
| * comparator. Thus, {@code comp1.equals(comp2)} implies that |
| * {@link Integer#signum signum}{@code (comp1.compare(o1, |
| * o2))==signum(comp2.compare(o1, o2))} for every object reference |
| * {@code o1} and {@code o2}.<p> |
| * |
| * Note that it is <i>always</i> safe <i>not</i> to override |
| * {@code Object.equals(Object)}. However, overriding this method may, |
| * in some cases, improve performance by allowing programs to determine |
| * that two distinct comparators impose the same order. |
| * |
| * @param obj the reference object with which to compare. |
| * @return {@code true} only if the specified object is also |
| * a comparator and it imposes the same ordering as this |
| * comparator. |
| * @see Object#equals(Object) |
| * @see Object#hashCode() |
| */ |
| boolean equals(Object obj); |
| |
| /** |
| * Returns a comparator that imposes the reverse ordering of this |
| * comparator. |
| * |
| * @return a comparator that imposes the reverse ordering of this |
| * comparator. |
| * @since 1.8 |
| */ |
| default Comparator<T> reversed() { |
| return Collections.reverseOrder(this); |
| } |
| |
| /** |
| * Returns a lexicographic-order comparator with another comparator. |
| * If this {@code Comparator} considers two elements equal, i.e. |
| * {@code compare(a, b) == 0}, {@code other} is used to determine the order. |
| * |
| * <p>The returned comparator is serializable if the specified comparator |
| * is also serializable. |
| * |
| * @apiNote |
| * For example, to sort a collection of {@code String} based on the length |
| * and then case-insensitive natural ordering, the comparator can be |
| * composed using following code, |
| * |
| * <pre>{@code |
| * Comparator<String> cmp = Comparator.comparingInt(String::length) |
| * .thenComparing(String.CASE_INSENSITIVE_ORDER); |
| * }</pre> |
| * |
| * @param other the other comparator to be used when this comparator |
| * compares two objects that are equal. |
| * @return a lexicographic-order comparator composed of this and then the |
| * other comparator |
| * @throws NullPointerException if the argument is null. |
| * @since 1.8 |
| */ |
| default Comparator<T> thenComparing(Comparator<? super T> other) { |
| Objects.requireNonNull(other); |
| return (Comparator<T> & Serializable) (c1, c2) -> { |
| int res = compare(c1, c2); |
| return (res != 0) ? res : other.compare(c1, c2); |
| }; |
| } |
| |
| /** |
| * Returns a lexicographic-order comparator with a function that |
| * extracts a key to be compared with the given {@code Comparator}. |
| * |
| * @implSpec This default implementation behaves as if {@code |
| * thenComparing(comparing(keyExtractor, cmp))}. |
| * |
| * @param <U> the type of the sort key |
| * @param keyExtractor the function used to extract the sort key |
| * @param keyComparator the {@code Comparator} used to compare the sort key |
| * @return a lexicographic-order comparator composed of this comparator |
| * and then comparing on the key extracted by the keyExtractor function |
| * @throws NullPointerException if either argument is null. |
| * @see #comparing(Function, Comparator) |
| * @see #thenComparing(Comparator) |
| * @since 1.8 |
| */ |
| default <U> Comparator<T> thenComparing( |
| Function<? super T, ? extends U> keyExtractor, |
| Comparator<? super U> keyComparator) |
| { |
| return thenComparing(comparing(keyExtractor, keyComparator)); |
| } |
| |
| /** |
| * Returns a lexicographic-order comparator with a function that |
| * extracts a {@code Comparable} sort key. |
| * |
| * @implSpec This default implementation behaves as if {@code |
| * thenComparing(comparing(keyExtractor))}. |
| * |
| * @param <U> the type of the {@link Comparable} sort key |
| * @param keyExtractor the function used to extract the {@link |
| * Comparable} sort key |
| * @return a lexicographic-order comparator composed of this and then the |
| * {@link Comparable} sort key. |
| * @throws NullPointerException if the argument is null. |
| * @see #comparing(Function) |
| * @see #thenComparing(Comparator) |
| * @since 1.8 |
| */ |
| default <U extends Comparable<? super U>> Comparator<T> thenComparing( |
| Function<? super T, ? extends U> keyExtractor) |
| { |
| return thenComparing(comparing(keyExtractor)); |
| } |
| |
| /** |
| * Returns a lexicographic-order comparator with a function that |
| * extracts an {@code int} sort key. |
| * |
| * @implSpec This default implementation behaves as if {@code |
| * thenComparing(comparingInt(keyExtractor))}. |
| * |
| * @param keyExtractor the function used to extract the integer sort key |
| * @return a lexicographic-order comparator composed of this and then the |
| * {@code int} sort key |
| * @throws NullPointerException if the argument is null. |
| * @see #comparingInt(ToIntFunction) |
| * @see #thenComparing(Comparator) |
| * @since 1.8 |
| */ |
| default Comparator<T> thenComparingInt(ToIntFunction<? super T> keyExtractor) { |
| return thenComparing(comparingInt(keyExtractor)); |
| } |
| |
| /** |
| * Returns a lexicographic-order comparator with a function that |
| * extracts a {@code long} sort key. |
| * |
| * @implSpec This default implementation behaves as if {@code |
| * thenComparing(comparingLong(keyExtractor))}. |
| * |
| * @param keyExtractor the function used to extract the long sort key |
| * @return a lexicographic-order comparator composed of this and then the |
| * {@code long} sort key |
| * @throws NullPointerException if the argument is null. |
| * @see #comparingLong(ToLongFunction) |
| * @see #thenComparing(Comparator) |
| * @since 1.8 |
| */ |
| default Comparator<T> thenComparingLong(ToLongFunction<? super T> keyExtractor) { |
| return thenComparing(comparingLong(keyExtractor)); |
| } |
| |
| /** |
| * Returns a lexicographic-order comparator with a function that |
| * extracts a {@code double} sort key. |
| * |
| * @implSpec This default implementation behaves as if {@code |
| * thenComparing(comparingDouble(keyExtractor))}. |
| * |
| * @param keyExtractor the function used to extract the double sort key |
| * @return a lexicographic-order comparator composed of this and then the |
| * {@code double} sort key |
| * @throws NullPointerException if the argument is null. |
| * @see #comparingDouble(ToDoubleFunction) |
| * @see #thenComparing(Comparator) |
| * @since 1.8 |
| */ |
| default Comparator<T> thenComparingDouble(ToDoubleFunction<? super T> keyExtractor) { |
| return thenComparing(comparingDouble(keyExtractor)); |
| } |
| |
| /** |
| * Returns a comparator that imposes the reverse of the <em>natural |
| * ordering</em>. |
| * |
| * <p>The returned comparator is serializable and throws {@link |
| * NullPointerException} when comparing {@code null}. |
| * |
| * @param <T> the {@link Comparable} type of element to be compared |
| * @return a comparator that imposes the reverse of the <i>natural |
| * ordering</i> on {@code Comparable} objects. |
| * @see Comparable |
| * @since 1.8 |
| */ |
| public static <T extends Comparable<? super T>> Comparator<T> reverseOrder() { |
| return Collections.reverseOrder(); |
| } |
| |
| /** |
| * Returns a comparator that compares {@link Comparable} objects in natural |
| * order. |
| * |
| * <p>The returned comparator is serializable and throws {@link |
| * NullPointerException} when comparing {@code null}. |
| * |
| * @param <T> the {@link Comparable} type of element to be compared |
| * @return a comparator that imposes the <i>natural ordering</i> on {@code |
| * Comparable} objects. |
| * @see Comparable |
| * @since 1.8 |
| */ |
| @SuppressWarnings("unchecked") |
| public static <T extends Comparable<? super T>> Comparator<T> naturalOrder() { |
| return (Comparator<T>) Comparators.NaturalOrderComparator.INSTANCE; |
| } |
| |
| /** |
| * Returns a null-friendly comparator that considers {@code null} to be |
| * less than non-null. When both are {@code null}, they are considered |
| * equal. If both are non-null, the specified {@code Comparator} is used |
| * to determine the order. If the specified comparator is {@code null}, |
| * then the returned comparator considers all non-null values to be equal. |
| * |
| * <p>The returned comparator is serializable if the specified comparator |
| * is serializable. |
| * |
| * @param <T> the type of the elements to be compared |
| * @param comparator a {@code Comparator} for comparing non-null values |
| * @return a comparator that considers {@code null} to be less than |
| * non-null, and compares non-null objects with the supplied |
| * {@code Comparator}. |
| * @since 1.8 |
| */ |
| public static <T> Comparator<T> nullsFirst(Comparator<? super T> comparator) { |
| return new Comparators.NullComparator<>(true, comparator); |
| } |
| |
| /** |
| * Returns a null-friendly comparator that considers {@code null} to be |
| * greater than non-null. When both are {@code null}, they are considered |
| * equal. If both are non-null, the specified {@code Comparator} is used |
| * to determine the order. If the specified comparator is {@code null}, |
| * then the returned comparator considers all non-null values to be equal. |
| * |
| * <p>The returned comparator is serializable if the specified comparator |
| * is serializable. |
| * |
| * @param <T> the type of the elements to be compared |
| * @param comparator a {@code Comparator} for comparing non-null values |
| * @return a comparator that considers {@code null} to be greater than |
| * non-null, and compares non-null objects with the supplied |
| * {@code Comparator}. |
| * @since 1.8 |
| */ |
| public static <T> Comparator<T> nullsLast(Comparator<? super T> comparator) { |
| return new Comparators.NullComparator<>(false, comparator); |
| } |
| |
| /** |
| * Accepts a function that extracts a sort key from a type {@code T}, and |
| * returns a {@code Comparator<T>} that compares by that sort key using |
| * the specified {@link Comparator}. |
| * |
| * <p>The returned comparator is serializable if the specified function |
| * and comparator are both serializable. |
| * |
| * @apiNote |
| * For example, to obtain a {@code Comparator} that compares {@code |
| * Person} objects by their last name ignoring case differences, |
| * |
| * <pre>{@code |
| * Comparator<Person> cmp = Comparator.comparing( |
| * Person::getLastName, |
| * String.CASE_INSENSITIVE_ORDER); |
| * }</pre> |
| * |
| * @param <T> the type of element to be compared |
| * @param <U> the type of the sort key |
| * @param keyExtractor the function used to extract the sort key |
| * @param keyComparator the {@code Comparator} used to compare the sort key |
| * @return a comparator that compares by an extracted key using the |
| * specified {@code Comparator} |
| * @throws NullPointerException if either argument is null |
| * @since 1.8 |
| */ |
| public static <T, U> Comparator<T> comparing( |
| Function<? super T, ? extends U> keyExtractor, |
| Comparator<? super U> keyComparator) |
| { |
| Objects.requireNonNull(keyExtractor); |
| Objects.requireNonNull(keyComparator); |
| return (Comparator<T> & Serializable) |
| (c1, c2) -> keyComparator.compare(keyExtractor.apply(c1), |
| keyExtractor.apply(c2)); |
| } |
| |
| /** |
| * Accepts a function that extracts a {@link java.lang.Comparable |
| * Comparable} sort key from a type {@code T}, and returns a {@code |
| * Comparator<T>} that compares by that sort key. |
| * |
| * <p>The returned comparator is serializable if the specified function |
| * is also serializable. |
| * |
| * @apiNote |
| * For example, to obtain a {@code Comparator} that compares {@code |
| * Person} objects by their last name, |
| * |
| * <pre>{@code |
| * Comparator<Person> byLastName = Comparator.comparing(Person::getLastName); |
| * }</pre> |
| * |
| * @param <T> the type of element to be compared |
| * @param <U> the type of the {@code Comparable} sort key |
| * @param keyExtractor the function used to extract the {@link |
| * Comparable} sort key |
| * @return a comparator that compares by an extracted key |
| * @throws NullPointerException if the argument is null |
| * @since 1.8 |
| */ |
| public static <T, U extends Comparable<? super U>> Comparator<T> comparing( |
| Function<? super T, ? extends U> keyExtractor) |
| { |
| Objects.requireNonNull(keyExtractor); |
| return (Comparator<T> & Serializable) |
| (c1, c2) -> keyExtractor.apply(c1).compareTo(keyExtractor.apply(c2)); |
| } |
| |
| /** |
| * Accepts a function that extracts an {@code int} sort key from a type |
| * {@code T}, and returns a {@code Comparator<T>} that compares by that |
| * sort key. |
| * |
| * <p>The returned comparator is serializable if the specified function |
| * is also serializable. |
| * |
| * @param <T> the type of element to be compared |
| * @param keyExtractor the function used to extract the integer sort key |
| * @return a comparator that compares by an extracted key |
| * @see #comparing(Function) |
| * @throws NullPointerException if the argument is null |
| * @since 1.8 |
| */ |
| public static <T> Comparator<T> comparingInt(ToIntFunction<? super T> keyExtractor) { |
| Objects.requireNonNull(keyExtractor); |
| return (Comparator<T> & Serializable) |
| (c1, c2) -> Integer.compare(keyExtractor.applyAsInt(c1), keyExtractor.applyAsInt(c2)); |
| } |
| |
| /** |
| * Accepts a function that extracts a {@code long} sort key from a type |
| * {@code T}, and returns a {@code Comparator<T>} that compares by that |
| * sort key. |
| * |
| * <p>The returned comparator is serializable if the specified function is |
| * also serializable. |
| * |
| * @param <T> the type of element to be compared |
| * @param keyExtractor the function used to extract the long sort key |
| * @return a comparator that compares by an extracted key |
| * @see #comparing(Function) |
| * @throws NullPointerException if the argument is null |
| * @since 1.8 |
| */ |
| public static <T> Comparator<T> comparingLong(ToLongFunction<? super T> keyExtractor) { |
| Objects.requireNonNull(keyExtractor); |
| return (Comparator<T> & Serializable) |
| (c1, c2) -> Long.compare(keyExtractor.applyAsLong(c1), keyExtractor.applyAsLong(c2)); |
| } |
| |
| /** |
| * Accepts a function that extracts a {@code double} sort key from a type |
| * {@code T}, and returns a {@code Comparator<T>} that compares by that |
| * sort key. |
| * |
| * <p>The returned comparator is serializable if the specified function |
| * is also serializable. |
| * |
| * @param <T> the type of element to be compared |
| * @param keyExtractor the function used to extract the double sort key |
| * @return a comparator that compares by an extracted key |
| * @see #comparing(Function) |
| * @throws NullPointerException if the argument is null |
| * @since 1.8 |
| */ |
| public static<T> Comparator<T> comparingDouble(ToDoubleFunction<? super T> keyExtractor) { |
| Objects.requireNonNull(keyExtractor); |
| return (Comparator<T> & Serializable) |
| (c1, c2) -> Double.compare(keyExtractor.applyAsDouble(c1), keyExtractor.applyAsDouble(c2)); |
| } |
| } |
