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

All Superinterfaces:

java.util.Map

All Known Subinterfaces:

ConcurrentNavigableMap

All Known Implementing Classes:

ConcurrentHashMap, ConcurrentSkipListMap

public interface ConcurrentMap

extends java.util.Map

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 as a key or value happen-before actions subsequent to the access or removal of that object from the in another thread.

This interface is a member of the Java Collections Framework.

Since:

1.5

Author:

Doug Lea

Nested Class Summary

Nested classes inherited from class java.util.Map

java.util.Map.Entry

Method Summary

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

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

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

remove

public boolean remove(java.lang.Object key,
                      java.lang.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:

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

java.lang.ClassCastException - if the key or value is of an inappropriate type for this map (optional)

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

replace

public boolean replace(java.lang.Object key,
                       java.lang.Object oldValue,
                       java.lang.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:

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

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

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

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

replace

public java.lang.Object replace(java.lang.Object key,
                                java.lang.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:

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

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