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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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|
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package java.util.concurrent; |
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import java.util.Map; |
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|
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/** |
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* A {@link java.util.Map} providing thread safety and atomicity |
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* guarantees. |
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* |
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* <p>Memory consistency effects: As with other concurrent |
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* collections, actions in a thread prior to placing an object into a |
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* {@code ConcurrentMap} as a key or value |
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* <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a> |
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* actions subsequent to the access or removal of that object from |
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* the {@code ConcurrentMap} in another thread. |
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* |
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* <p>This interface is a member of the |
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* <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
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* Java Collections Framework</a>. |
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* |
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* @since 1.5 |
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* @author Doug Lea |
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* @param <K> the type of keys maintained by this map |
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* @param <V> the type of mapped values |
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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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/** |
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* {@inheritDoc} |
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* |
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* @implNote This implementation assumes that the ConcurrentMap cannot |
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* contain null values and get() returning null unambiguously means the key |
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* is absent. Implementations which support null values must override this |
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* default implementation. |
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*/ |
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@Override |
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default V getOrDefault(Object key, V defaultValue) { |
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V v; |
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return ((v = get(key)) != null) ? v : defaultValue; |
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} |
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|
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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> {@code |
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* if (!map.containsKey(key)) |
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* return map.put(key, value); |
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* else |
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* return map.get(key);}</pre> |
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* |
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* except that the action is performed atomically. |
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* |
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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 the previous value associated with the specified key, or |
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* {@code null} if there was no mapping for the key. |
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* (A {@code null} return can also indicate that the map |
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* previously associated {@code null} with the key, |
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* if the implementation supports null values.) |
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* @throws UnsupportedOperationException if the {@code put} operation |
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* is 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 NullPointerException if the specified key or value is null, |
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* and this map does not permit null keys or values |
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* @throws IllegalArgumentException if some property of the specified key |
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* or value prevents it from being stored in this map |
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*/ |
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V putIfAbsent(K key, V value); |
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|
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/** |
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* Removes the entry for a key only if currently mapped to a given value. |
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* This is equivalent to |
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* <pre> {@code |
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* if (map.containsKey(key) && Objects.equals(map.get(key), value)) { |
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* map.remove(key); |
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* return true; |
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* } else |
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* return false;}</pre> |
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* |
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* except that the action is performed atomically. |
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* |
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* @param key key with which the specified value is associated |
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* @param value value expected to be associated with the specified key |
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* @return {@code true} if the value was removed |
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* @throws UnsupportedOperationException if the {@code remove} operation |
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* is not supported by this map |
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* @throws ClassCastException if the key or value is of an inappropriate |
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* type for this map |
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* (<a href="../Collection.html#optional-restrictions">optional</a>) |
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* @throws NullPointerException if the specified key or value is null, |
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* and this map does not permit null keys or values |
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* (<a href="../Collection.html#optional-restrictions">optional</a>) |
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*/ |
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boolean remove(Object key, Object value); |
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|
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/** |
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* Replaces the entry for a key only if currently mapped to a given value. |
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* This is equivalent to |
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* <pre> {@code |
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* if (map.containsKey(key) && Objects.equals(map.get(key), oldValue)) { |
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* map.put(key, newValue); |
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* return true; |
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* } else |
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* return false;}</pre> |
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* |
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* except that the action is performed atomically. |
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* |
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* @param key key with which the specified value is associated |
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* @param oldValue value expected to be associated with the specified key |
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* @param newValue value to be associated with the specified key |
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* @return {@code true} if the value was replaced |
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* @throws UnsupportedOperationException if the {@code put} operation |
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* is not supported by this map |
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* @throws ClassCastException if the class of a specified key or value |
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* prevents it from being stored in this map |
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* @throws NullPointerException if a specified key or value is null, |
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* and this map does not permit null keys or values |
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* @throws IllegalArgumentException if some property of a specified key |
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* or value prevents it from being stored in this map |
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*/ |
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boolean replace(K key, V oldValue, V newValue); |
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|
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/** |
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* Replaces the entry for a key only if currently mapped to some value. |
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* This is equivalent to |
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* <pre> {@code |
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* if (map.containsKey(key)) { |
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* return map.put(key, value); |
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* } else |
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* return null;}</pre> |
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* |
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* except that the action is performed atomically. |
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* |
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* @param key key with which the specified value is associated |
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* @param value value to be associated with the specified key |
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* @return the previous value associated with the specified key, or |
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* {@code null} if there was no mapping for the key. |
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* (A {@code null} return can also indicate that the map |
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* previously associated {@code null} with the key, |
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* if the implementation supports null values.) |
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* @throws UnsupportedOperationException if the {@code put} operation |
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* is 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 NullPointerException if the specified key or value is null, |
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* and this map does not permit null keys or values |
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* @throws IllegalArgumentException if some property of the specified key |
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* or value prevents it from being stored in this map |
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*/ |
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V replace(K key, V value); |
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} |
