1 /* 2 * Copyright (c) 2017, 2019, 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. 8 * 9 * This code is distributed in the hope that it will be useful, but WITHOUT 10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or 11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License 12 * version 2 for more details (a copy is included in the LICENSE file that 13 * accompanied this code). 14 * 15 * You should have received a copy of the GNU General Public License version 16 * 2 along with this work; if not, write to the Free Software Foundation, 17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. 18 * 19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA 20 * or visit www.oracle.com if you need additional information or have any 21 * questions. 22 */ 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 package jdk.internal.vm.compiler.collections; 42 43 /** 44 * Strategy for comparing two objects. Default predefined strategies are {@link #DEFAULT}, 45 * {@link #IDENTITY}, and {@link #IDENTITY_WITH_SYSTEM_HASHCODE}. 46 * 47 * @since 19.0 48 */ 49 public abstract class Equivalence { 50 51 /** 52 * Default equivalence calling {@link #equals(Object)} to check equality and {@link #hashCode()} 53 * for obtaining hash values. Do not change the logic of this class as it may be inlined in 54 * other places. 55 * 56 * @since 19.0 57 */ 58 public static final Equivalence DEFAULT = new Equivalence() { 59 60 @Override 61 public boolean equals(Object a, Object b) { 62 return a.equals(b); 63 } 64 65 @Override 66 public int hashCode(Object o) { 67 return o.hashCode(); 68 } 69 }; 70 71 /** 72 * Identity equivalence using {@code ==} to check equality and {@link #hashCode()} for obtaining 73 * hash values. Do not change the logic of this class as it may be inlined in other places. 74 * 75 * @since 19.0 76 */ 77 public static final Equivalence IDENTITY = new Equivalence() { 78 79 @Override 80 public boolean equals(Object a, Object b) { 81 return a == b; 82 } 83 84 @Override 85 public int hashCode(Object o) { 86 return o.hashCode(); 87 } 88 }; 89 90 /** 91 * Identity equivalence using {@code ==} to check equality and 92 * {@link System#identityHashCode(Object)} for obtaining hash values. Do not change the logic of 93 * this class as it may be inlined in other places. 94 * 95 * @since 19.0 96 */ 97 public static final Equivalence IDENTITY_WITH_SYSTEM_HASHCODE = new Equivalence() { 98 99 @Override 100 public boolean equals(Object a, Object b) { 101 return a == b; 102 } 103 104 @Override 105 public int hashCode(Object o) { 106 return System.identityHashCode(o); 107 } 108 }; 109 110 /** 111 * Subclass for creating custom equivalence definitions. 112 * 113 * @since 19.0 114 */ Equivalence()115 protected Equivalence() { 116 } 117 118 /** 119 * Returns {@code true} if the non-{@code null} arguments are equal to each other and 120 * {@code false} otherwise. 121 * 122 * @since 19.0 123 */ equals(Object a, Object b)124 public abstract boolean equals(Object a, Object b); 125 126 /** 127 * Returns the hash code of a non-{@code null} argument {@code o}. 128 * 129 * @since 19.0 130 */ hashCode(Object o)131 public abstract int hashCode(Object o); 132 } 133