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 package org.graalvm.util;

    24 

    25 /**

    26  * Strategy for comparing two objects. Default predefined strategies are {@link #DEFAULT},

    27  * {@link #IDENTITY}, and {@link #IDENTITY_WITH_SYSTEM_HASHCODE}.

    28  */

    29 public abstract class Equivalence {

    30 

    31     /**

    32      * Default equivalence calling {@link #equals(Object)} to check equality and {@link #hashCode()}

    33      * for obtaining hash values. Do not change the logic of this class as it may be inlined in

    34      * other places.

    35      */

    36     public static final Equivalence DEFAULT = new Equivalence() {

    37 

    38         @Override

    39         public boolean equals(Object a, Object b) {

    40             return a.equals(b);

    41         }

    42 

    43         @Override

    44         public int hashCode(Object o) {

    45             return o.hashCode();

    46         }

    47     };

    48 

    49     /**

    50      * Identity equivalence using {@code ==} to check equality and {@link #hashCode()} for obtaining

    51      * hash values. Do not change the logic of this class as it may be inlined in other places.

    52      */

    53     public static final Equivalence IDENTITY = new Equivalence() {

    54 

    55         @Override

    56         public boolean equals(Object a, Object b) {

    57             return a == b;

    58         }

    59 

    60         @Override

    61         public int hashCode(Object o) {

    62             return o.hashCode();

    63         }

    64     };

    65 

    66     /**

    67      * Identity equivalence using {@code ==} to check equality and

    68      * {@link System#identityHashCode(Object)} for obtaining hash values. Do not change the logic of

    69      * this class as it may be inlined in other places.

    70      */

    71     public static final Equivalence IDENTITY_WITH_SYSTEM_HASHCODE = new Equivalence() {

    72 

    73         @Override

    74         public boolean equals(Object a, Object b) {

    75             return a == b;

    76         }

    77 

    78         @Override

    79         public int hashCode(Object o) {

    80             return System.identityHashCode(o);

    81         }

    82     };

    83 

    84     /**

    85      * Subclass for creating custom equivalence definitions.

    86      */

    87     protected Equivalence() {

    88     }

    89 

    90     public abstract boolean equals(Object a, Object b);

    91 

    92     public abstract int hashCode(Object o);

    93 }