java.util.concurrent

Interface ConcurrentMap<K,V>

All Superinterfaces:
Map<K,V>
Known Subinterfaces:
ConcurrentNavigableMap<K,V>
Known Implementing Classes:
ConcurrentHashMap<K,V>, ConcurrentSkipListMap<K,V>

public interface ConcurrentMap<K,V>
extends Map<K,V>

A Map providing additional atomic putIfAbsent, remove, and replace methods.

Memory consistency effects: As with other concurrent collections, actions in a thread prior to placing an object into a ConcurrentMap as a key or value happen-before actions subsequent to the access or removal of that object from the ConcurrentMap in another thread.

This interface is a member of the ../../../../technotes/guides/collections/index.html"> Java Collections Framework.

Since:
1.5

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(Object key, Object value)
Removes the entry for a key only if currently mapped to a given value.
V
replace(K key, V value)
Replaces the entry for a key only if currently mapped to some value.
boolean
replace(K key, V oldValue, V newValue)
Replaces the entry for a key only if currently mapped to a given value.

Methods inherited from interface java.util.Map<K,V>

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

Method Details

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:
the previous value associated with the specified key, or null if there was no mapping for the key. (A null return can also indicate that the map previously associated null with the key, if the implementation supports null values.)
Throws:
UnsupportedOperationException - if the put operation is not supported by this map
ClassCastException - if the class of the specified key or value prevents it from being stored in this map
NullPointerException - if the specified key or value is null, and this map does not permit null keys or values
IllegalArgumentException - if some property of the specified key or value prevents it from being stored in this map

remove

public boolean remove(Object key,
                      Object value)
Removes the entry for a key only if currently mapped to a given value. This is equivalent to
   if (map.containsKey(key) && 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 expected to be associated with the specified key
Returns:
true if the value was removed
Throws:
UnsupportedOperationException - if the remove operation is not supported by this map
ClassCastException - if the key or value is of an inappropriate type for this map (optional)
NullPointerException - if the specified key or value is null, and this map does not permit null keys or values (optional)

replace

public V replace(K key,
                 V value)
Replaces the entry for a key only if currently mapped to some value. This is equivalent to
   if (map.containsKey(key)) {
       return map.put(key, value);
   } else return null;
except that the action is performed atomically.
Parameters:
key - key with which the specified value is associated
value - value to be associated with the specified key
Returns:
the previous value associated with the specified key, or null if there was no mapping for the key. (A null return can also indicate that the map previously associated null with the key, if the implementation supports null values.)
Throws:
UnsupportedOperationException - if the put operation is not supported by this map
ClassCastException - if the class of the specified key or value prevents it from being stored in this map
NullPointerException - if the specified key or value is null, and this map does not permit null keys or values
IllegalArgumentException - if some property of the specified key or value prevents it from being stored in this map

replace

public boolean replace(K key,
                       V oldValue,
                       V newValue)
Replaces the entry for a key only if currently mapped to a given value. This is equivalent to
   if (map.containsKey(key) && map.get(key).equals(oldValue)) {
       map.put(key, newValue);
       return true;
   } else return false;
except that the action is performed atomically.
Parameters:
key - key with which the specified value is associated
oldValue - value expected to be associated with the specified key
newValue - value to be associated with the specified key
Returns:
true if the value was replaced
Throws:
UnsupportedOperationException - if the put operation is not supported by this map
ClassCastException - if the class of a specified key or value prevents it from being stored in this map
NullPointerException - if a specified key or value is null, and this map does not permit null keys or values
IllegalArgumentException - if some property of a specified key or value prevents it from being stored in this map