1 |
/* |
2 |
* Copyright (c) 2015, 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. Oracle designates this |
8 |
* particular file as subject to the "Classpath" exception as provided |
9 |
* by Oracle in the LICENSE file that accompanied this code. |
10 |
* |
11 |
* This code is distributed in the hope that it will be useful, but WITHOUT |
12 |
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
13 |
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
14 |
* version 2 for more details (a copy is included in the LICENSE file that |
15 |
* accompanied this code). |
16 |
* |
17 |
* You should have received a copy of the GNU General Public License version |
18 |
* 2 along with this work; if not, write to the Free Software Foundation, |
19 |
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
20 |
* |
21 |
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
22 |
* or visit www.oracle.com if you need additional information or have any |
23 |
* questions. |
24 |
*/ |
25 |
|
26 |
package java.util; |
27 |
|
28 |
/** |
29 |
* An immutable container for a key and a value, suitable for use |
30 |
* in creating and populating {@code Map} instances. |
31 |
* |
32 |
* <p>This is a <a href="../lang/doc-files/ValueBased.html">value-based</a> |
33 |
* class; use of identity-sensitive operations (including reference equality |
34 |
* ({@code ==}), identity hash code, or synchronization) on instances of |
35 |
* {@code KeyValueHolder} may have unpredictable results and should be avoided. |
36 |
* |
37 |
* @apiNote |
38 |
* This class is not public. Instances can be created using the |
39 |
* {@link Map#entry Map.entry(k, v)} factory method, which is public. |
40 |
* |
41 |
* <p>This class differs from AbstractMap.SimpleImmutableEntry in the following ways: |
42 |
* it is not serializable, it is final, and its key and value must be non-null. |
43 |
* |
44 |
* @param <K> the key type |
45 |
* @param <V> the value type |
46 |
* |
47 |
* @see Map#ofEntries Map.ofEntries() |
48 |
* @since 9 |
49 |
*/ |
50 |
final class KeyValueHolder<K,V> implements Map.Entry<K,V> { |
51 |
final K key; |
52 |
final V value; |
53 |
|
54 |
KeyValueHolder(K k, V v) { |
55 |
key = Objects.requireNonNull(k); |
56 |
value = Objects.requireNonNull(v); |
57 |
} |
58 |
|
59 |
/** |
60 |
* Gets the key from this holder. |
61 |
* |
62 |
* @return the key |
63 |
*/ |
64 |
@Override |
65 |
public K getKey() { |
66 |
return key; |
67 |
} |
68 |
|
69 |
/** |
70 |
* Gets the value from this holder. |
71 |
* |
72 |
* @return the value |
73 |
*/ |
74 |
@Override |
75 |
public V getValue() { |
76 |
return value; |
77 |
} |
78 |
|
79 |
/** |
80 |
* Throws {@link UnsupportedOperationException}. |
81 |
* |
82 |
* @param value ignored |
83 |
* @return never returns normally |
84 |
*/ |
85 |
@Override |
86 |
public V setValue(V value) { |
87 |
throw new UnsupportedOperationException("not supported"); |
88 |
} |
89 |
|
90 |
/** |
91 |
* Compares the specified object with this entry for equality. |
92 |
* Returns {@code true} if the given object is also a map entry and |
93 |
* the two entries' keys and values are equal. Note that key and |
94 |
* value are non-null, so equals() can be called safely on them. |
95 |
*/ |
96 |
@Override |
97 |
public boolean equals(Object o) { |
98 |
if (!(o instanceof Map.Entry)) |
99 |
return false; |
100 |
Map.Entry<?,?> e = (Map.Entry<?,?>)o; |
101 |
return key.equals(e.getKey()) && value.equals(e.getValue()); |
102 |
} |
103 |
|
104 |
/** |
105 |
* Returns the hash code value for this map entry. The hash code |
106 |
* is {@code key.hashCode() ^ value.hashCode()}. Note that key and |
107 |
* value are non-null, so hashCode() can be called safely on them. |
108 |
*/ |
109 |
@Override |
110 |
public int hashCode() { |
111 |
return key.hashCode() ^ value.hashCode(); |
112 |
} |
113 |
|
114 |
/** |
115 |
* Returns a String representation of this map entry. This |
116 |
* implementation returns the string representation of this |
117 |
* entry's key followed by the equals character ("{@code =}") |
118 |
* followed by the string representation of this entry's value. |
119 |
* |
120 |
* @return a String representation of this map entry |
121 |
*/ |
122 |
@Override |
123 |
public String toString() { |
124 |
return key + "=" + value; |
125 |
} |
126 |
} |