edu.emory.mathcs.backport.java.util.concurrent

Interface ConcurrentMap

public interface ConcurrentMap extends Map

A 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.

Since: 1.5

Author: Doug Lea

Method Summary
ObjectputIfAbsent(Object key, Object value)
If the specified key is not already associated with a value, associate it with the given value.
booleanremove(Object key, Object value)
Removes the entry for a key only if currently mapped to a given value.
booleanreplace(Object key, Object oldValue, Object newValue)
Replaces the entry for a key only if currently mapped to a given value.
Objectreplace(Object key, Object value)
Replaces the entry for a key only if currently mapped to some value.

Method Detail

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.)

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 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

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

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.)

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