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package java.util.concurrent; |
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|
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import java.util.Map; |
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|
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/** |
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* A ConcurrentMap is a Map providing an additional atomic |
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* <tt>putIfAbsent</tt> method. |
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**/ |
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public interface ConcurrentMap<K, V> extends Map<K, V> { |
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/** |
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* If the specified key is not already associated |
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* with a value, associate it with the given value. |
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* This is equivalent to |
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* <pre> |
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* if (!map.containsKey(key)) map.put(key, value); |
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* return get(key); |
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* </pre> |
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* Except that the action is performed atomically. |
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* @param key key with which the specified value is to be associated. |
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* @param value value to be associated with the specified key. |
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* @return previous value associated with specified key, or <tt>null</tt> |
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* if there was no mapping for key. A <tt>null</tt> return can |
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* also indicate that the map previously associated <tt>null</tt> |
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* with the specified key, if the implementation supports |
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* <tt>null</tt> values. |
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* |
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* @throws UnsupportedOperationException if the <tt>put</tt> operation is |
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* not supported by this map. |
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* @throws ClassCastException if the class of the specified key or value |
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* prevents it from being stored in this map. |
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* @throws IllegalArgumentException if some aspect of this key or value |
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* prevents it from being stored in this map. |
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* @throws NullPointerException this map does not permit <tt>null</tt> |
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* keys or values, and the specified key or value is |
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* <tt>null</tt>. |
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* |
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**/ |
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public V putIfAbsent(K key, V value); |
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} |
