java.util.concurrent
interface ConcurrentMap

All Superinterfaces:

Map

All Known Implementing Classes:

ConcurrentHashMap

public interface ConcurrentMap
extends Map

A {@link java.util.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 {@code ConcurrentMap} as a key or value happen-before actions subsequent to the access or removal of that object from the {@code ConcurrentMap} in another thread.

This interface is a member of the Java Collections Framework.

putIfAbsent

public Object putIfAbsent(Object key,
                          Object 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.)

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

replace

public Object replace(Object key,
                      Object 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.)

replace

public boolean replace(Object key,
                       Object oldValue,
                       Object 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