Java Doc for ReferenceIdentityMap.java in  » Library » Apache-common-Collections » org » apache » commons » collections » map » Java Source Code / Java DocumentationJava Source Code and Java Documentation

When you construct a ReferenceIdentityMap, you can specify what kind of references are used to store the map's keys and values. If non-hard references are used, then the garbage collector can remove mappings if a key or value becomes unreachable, or if the JVM's memory is running low. For information on how the different reference types behave, see Reference .

Different types of references can be specified for keys and values. The default constructor uses hard keys and soft values, providing a memory-sensitive cache.

This map is similar to org.apache.commons.collections.map.ReferenceMap ReferenceMap . It differs in that keys and values in this class are compared using ==.

This map will violate the detail of various Map and map view contracts. As a general rule, don't compare this map to other maps.

This java.util.Map Map implementation does not allow null elements. Attempting to add a null key or value to the map will raise a NullPointerException.

This implementation is not synchronized. You can use java.util.Collections.synchronizedMap to provide synchronized access to a ReferenceIdentityMap. Remember that synchronization will not stop the garbage collecter removing entries.

All the available iterators can be reset back to the start by casting to ResettableIterator and calling reset().

Note that ReferenceIdentityMap is not synchronized and is not thread-safe. If you wish to use this map from multiple threads concurrently, you must use appropriate synchronization. The simplest approach is to wrap this map using java.util.Collections.synchronizedMap . This class may throw exceptions when accessed by concurrent threads without synchronization.
See Also:   java.lang.ref.Reference
since:
   Commons Collections 3.0 (previously in main package v2.1)
version:
   $Revision: 348007 $ $Date: 2005-11-21 22:52:57 +0000 (Mon, 21 Nov 2005) $
author:
   Stephen Colebourne

This implementation uses the identity hash code.
Parameters:
  key - the key to get a hash code for the hash code

This implementation uses the identity hash code.
Parameters:
  key - the key to get a hash code for, may be null
Parameters:
  value - the value to get a hash code for, may be null the hash code, as per the MapEntry specification

This implementation converts the key from the entry to a real reference before comparison and uses ==.
Parameters:
  key1 - the first key to compare passed in from outside
Parameters:
  key2 - the second key extracted from the entry via entry.key true if equal by identity

This implementation uses ==.
Parameters:
  value1 - the first value to compare passed in from outside
Parameters:
  value2 - the second value extracted from the entry via getValue() true if equal by identity