java.util.concurrent
Interface ConcurrentMap<K,V>

All Superinterfaces:

Map

All Known Implementing Classes:

ConcurrentHashMap

public interface ConcurrentMap<K,V>

extends Map<K,V>

A Map providing additional atomic putIfAbsent and remove methods.

Since:

1.5

Author:

Doug Lea

Nested Class Summary

Nested classes inherited from class java.util.Map

Map.Entry<K,V>

Method Summary

V	putIfAbsent(K key, V value) If the specified key is not already associated with a value, associate it with the given value.
boolean	remove(java.lang.Object key, java.lang.Object value) Remove entry for key only if currently mapped to given value.

Methods inherited from interface java.util.Map

clear, containsKey, containsValue, entrySet, equals, get, hashCode, isEmpty, keySet, put, putAll, remove, size, values

Method Detail

putIfAbsent

public V putIfAbsent(K key,
                     V value)

If the specified key is not already associated with a value, associate it with the given value. This is equivalent to

   if (!map.containsKey(key)) 
      return map.put(key, value);
   else
      return map.get(key);
 

Except that the action is performed atomically.

Parameters:

key - key with which the specified value is to be associated.

value - value to be associated with the specified key.

Returns:

previous value associated with specified key, or null if there was no mapping for key. A null return can also indicate that the map previously associated null with the specified key, if the implementation supports null values.

Throws:

java.lang.UnsupportedOperationException - if the put operation is not supported by this map.

java.lang.ClassCastException - if the class of the specified key or value prevents it from being stored in this map.

java.lang.IllegalArgumentException - if some aspect of this key or value prevents it from being stored in this map.

java.lang.NullPointerException - if this map does not permit null keys or values, and the specified key or value is null.

remove

public boolean remove(java.lang.Object key,
                      java.lang.Object value)

Remove entry for key only if currently mapped to given value. Acts as

 
  if (map.get(key).equals(value)) {
     map.remove(key);
     return true;
 } else return false;
 

except that the action is performed atomically.

Parameters:

key - key with which the specified value is associated.

value - value associated with the specified key.

Returns:

true if the value was removed

Throws:

java.lang.NullPointerException - if this map does not permit null keys or values, and the specified key or value is null.