1 /*
   2  * Copyright (c) 2017, 2017, 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 package jdk.internal.vm.compiler.collections;
  26 
  27 /**
  28  * Strategy for comparing two objects. Default predefined strategies are {@link #DEFAULT},
  29  * {@link #IDENTITY}, and {@link #IDENTITY_WITH_SYSTEM_HASHCODE}.
  30  *
  31  * @since 1.0
  32  */
  33 public abstract class Equivalence {
  34 
  35     /**
  36      * Default equivalence calling {@link #equals(Object)} to check equality and {@link #hashCode()}
  37      * for obtaining hash values. Do not change the logic of this class as it may be inlined in
  38      * other places.
  39      *
  40      * @since 1.0
  41      */
  42     public static final Equivalence DEFAULT = new Equivalence() {
  43 
  44         @Override
  45         public boolean equals(Object a, Object b) {
  46             return a.equals(b);
  47         }
  48 
  49         @Override
  50         public int hashCode(Object o) {
  51             return o.hashCode();
  52         }
  53     };
  54 
  55     /**
  56      * Identity equivalence using {@code ==} to check equality and {@link #hashCode()} for obtaining
  57      * hash values. Do not change the logic of this class as it may be inlined in other places.
  58      *
  59      * @since 1.0
  60      */
  61     public static final Equivalence IDENTITY = new Equivalence() {
  62 
  63         @Override
  64         public boolean equals(Object a, Object b) {
  65             return a == b;
  66         }
  67 
  68         @Override
  69         public int hashCode(Object o) {
  70             return o.hashCode();
  71         }
  72     };
  73 
  74     /**
  75      * Identity equivalence using {@code ==} to check equality and
  76      * {@link System#identityHashCode(Object)} for obtaining hash values. Do not change the logic of
  77      * this class as it may be inlined in other places.
  78      *
  79      * @since 1.0
  80      */
  81     public static final Equivalence IDENTITY_WITH_SYSTEM_HASHCODE = new Equivalence() {
  82 
  83         @Override
  84         public boolean equals(Object a, Object b) {
  85             return a == b;
  86         }
  87 
  88         @Override
  89         public int hashCode(Object o) {
  90             return System.identityHashCode(o);
  91         }
  92     };
  93 
  94     /**
  95      * Subclass for creating custom equivalence definitions.
  96      *
  97      * @since 1.0
  98      */
  99     protected Equivalence() {
 100     }
 101 
 102     /**
 103      * Returns {@code true} if the non-{@code null} arguments are equal to each other and
 104      * {@code false} otherwise.
 105      *
 106      * @since 1.0
 107      */
 108     public abstract boolean equals(Object a, Object b);
 109 
 110     /**
 111      * Returns the hash code of a non-{@code null} argument {@code o}.
 112      *
 113      * @since 1.0
 114      */
 115     public abstract int hashCode(Object o);
 116 }