public interface

ConcurrentMap

implements Map<K, V>
java.util.concurrent.ConcurrentMap<K, V>
Known Indirect Subclasses

Class Overview

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.

Summary

Public Methods
abstract V putIfAbsent(K key, V value)
If the specified key is not already associated with a value, associate it with the given value.
abstract boolean remove(Object key, Object value)
Removes the entry for a key only if currently mapped to a given value.
abstract boolean replace(K key, V oldValue, V newValue)
Replaces the entry for a key only if currently mapped to a given value.
abstract V replace(K key, V value)
Replaces the entry for a key only if currently mapped to some value.
[Expand]
Inherited Methods
From interface java.util.Map

Public Methods

public abstract V putIfAbsent (K key, V value)

Since: API Level 1

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

public abstract boolean remove (Object key, Object value)

Since: API Level 1

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)

public abstract boolean replace (K key, V oldValue, V newValue)

Since: API Level 1

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

public abstract V replace (K key, V value)

Since: API Level 1

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