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3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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13  * accompanied this code).
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22  */
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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