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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *   http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   * 
17   */
18  
19  package org.apache.commons.lang3.builder;
20  
21  // adapted from org.apache.axis.utils.IDKey
22  
23  /**
24   * Wrap an identity key (System.identityHashCode()) 
25   * so that an object can only be equal() to itself.
26   * 
27   * This is necessary to disambiguate the occasional duplicate
28   * identityHashCodes that can occur.
29   * 
30   */ 
31  final class IDKey {
32          private final Object value;
33          private final int id;
34  
35          /**
36           * Constructor for IDKey
37           * @param _value The value
38           */ 
39          public IDKey(final Object _value) {
40              // This is the Object hashcode 
41              id = System.identityHashCode(_value);  
42              // There have been some cases (LANG-459) that return the 
43              // same identity hash code for different objects.  So 
44              // the value is also added to disambiguate these cases.
45              value = _value;
46          }
47  
48          /**
49           * returns hashcode - i.e. the system identity hashcode.
50           * @return the hashcode
51           */ 
52          @Override
53          public int hashCode() {
54             return id;
55          }
56  
57          /**
58           * checks if instances are equal
59           * @param other The other object to compare to
60           * @return if the instances are for the same object
61           */ 
62          @Override
63          public boolean equals(final Object other) {
64              if (!(other instanceof IDKey)) {
65                  return false;
66              }
67              final IDKey idKey = (IDKey) other;
68              if (id != idKey.id) {
69                  return false;
70              }
71              // Note that identity equals is used.
72              return value == idKey.value;
73           }
74  }