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31 * Written by Doug Lea with assistance from members of JCP JSR-166
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36 package java.util.concurrent;
40 * A {@link java.util.Map} providing additional atomic
41 * <tt>putIfAbsent</tt>, <tt>remove</tt>, and <tt>replace</tt> methods.
43 * <p>Memory consistency effects: As with other concurrent
44 * collections, actions in a thread prior to placing an object into a
45 * {@code ConcurrentMap} as a key or value
46 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
47 * actions subsequent to the access or removal of that object from
48 * the {@code ConcurrentMap} in another thread.
50 * <p>This interface is a member of the
51 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
52 * Java Collections Framework</a>.
56 * @param <K> the type of keys maintained by this map
57 * @param <V> the type of mapped values
59 public interface ConcurrentMap<K, V> extends Map<K, V> {
61 * If the specified key is not already associated
62 * with a value, associate it with the given value.
63 * This is equivalent to
65 * if (!map.containsKey(key))
66 * return map.put(key, value);
68 * return map.get(key);</pre>
69 * except that the action is performed atomically.
71 * @param key key with which the specified value is to be associated
72 * @param value value to be associated with the specified key
73 * @return the previous value associated with the specified key, or
74 * <tt>null</tt> if there was no mapping for the key.
75 * (A <tt>null</tt> return can also indicate that the map
76 * previously associated <tt>null</tt> with the key,
77 * if the implementation supports null values.)
78 * @throws UnsupportedOperationException if the <tt>put</tt> operation
79 * is not supported by this map
80 * @throws ClassCastException if the class of the specified key or value
81 * prevents it from being stored in this map
82 * @throws NullPointerException if the specified key or value is null,
83 * and this map does not permit null keys or values
84 * @throws IllegalArgumentException if some property of the specified key
85 * or value prevents it from being stored in this map
88 V putIfAbsent(K key, V value);
91 * Removes the entry for a key only if currently mapped to a given value.
92 * This is equivalent to
94 * if (map.containsKey(key) && map.get(key).equals(value)) {
97 * } else return false;</pre>
98 * except that the action is performed atomically.
100 * @param key key with which the specified value is associated
101 * @param value value expected to be associated with the specified key
102 * @return <tt>true</tt> if the value was removed
103 * @throws UnsupportedOperationException if the <tt>remove</tt> operation
104 * is not supported by this map
105 * @throws ClassCastException if the key or value is of an inappropriate
107 * (<a href="../Collection.html#optional-restrictions">optional</a>)
108 * @throws NullPointerException if the specified key or value is null,
109 * and this map does not permit null keys or values
110 * (<a href="../Collection.html#optional-restrictions">optional</a>)
112 boolean remove(Object key, Object value);
115 * Replaces the entry for a key only if currently mapped to a given value.
116 * This is equivalent to
118 * if (map.containsKey(key) && map.get(key).equals(oldValue)) {
119 * map.put(key, newValue);
121 * } else return false;</pre>
122 * except that the action is performed atomically.
124 * @param key key with which the specified value is associated
125 * @param oldValue value expected to be associated with the specified key
126 * @param newValue value to be associated with the specified key
127 * @return <tt>true</tt> if the value was replaced
128 * @throws UnsupportedOperationException if the <tt>put</tt> operation
129 * is not supported by this map
130 * @throws ClassCastException if the class of a specified key or value
131 * prevents it from being stored in this map
132 * @throws NullPointerException if a specified key or value is null,
133 * and this map does not permit null keys or values
134 * @throws IllegalArgumentException if some property of a specified key
135 * or value prevents it from being stored in this map
137 boolean replace(K key, V oldValue, V newValue);
140 * Replaces the entry for a key only if currently mapped to some value.
141 * This is equivalent to
143 * if (map.containsKey(key)) {
144 * return map.put(key, value);
145 * } else return null;</pre>
146 * except that the action is performed atomically.
148 * @param key key with which the specified value is associated
149 * @param value value to be associated with the specified key
150 * @return the previous value associated with the specified key, or
151 * <tt>null</tt> if there was no mapping for the key.
152 * (A <tt>null</tt> return can also indicate that the map
153 * previously associated <tt>null</tt> with the key,
154 * if the implementation supports null values.)
155 * @throws UnsupportedOperationException if the <tt>put</tt> operation
156 * is not supported by this map
157 * @throws ClassCastException if the class of the specified key or value
158 * prevents it from being stored in this map
159 * @throws NullPointerException if the specified key or value is null,
160 * and this map does not permit null keys or values
161 * @throws IllegalArgumentException if some property of the specified key
162 * or value prevents it from being stored in this map
164 V replace(K key, V value);