org.apache.commons.collections
public class LRUMap extends SequencedHashMap implements Externalizable
Deprecated: Moved to map subpackage. Due to be removed in v4.0.
An implementation of a Map which has a maximum size and uses a Least Recently Used algorithm to remove items from the Map when the maximum size is reached and new items are added.
A synchronized version can be obtained with:
Collections.synchronizedMap( theMapToSynchronize )
If it will be accessed by multiple threads, you _must_ synchronize access
to this Map. Even concurrent get(Object) operations produce indeterminate
behaviour.
Unlike the Collections 1.0 version, this version of LRUMap does use a true LRU algorithm. The keys for all gets and puts are moved to the front of the list. LRUMap is now a subclass of SequencedHashMap, and the "LRU" key is now equivalent to LRUMap.getFirst().
Since: Commons Collections 1.0
Version: $Revision: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $
Constructor Summary | |
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LRUMap()
Default constructor, primarily for the purpose of
de-externalization. | |
LRUMap(int i)
Create a new LRUMap with a maximum capacity of i.
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Method Summary | |
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Object | get(Object key) Get the value for a key from the Map. |
int | getMaximumSize() Getter for property maximumSize. |
protected void | processRemovedLRU(Object key, Object value)
Subclasses of LRUMap may hook into this method to
provide specialized actions whenever an Object is
automatically removed from the cache. |
Object | put(Object key, Object value) Removes the key and its Object from the Map. (Note: this may result in the "Least Recently Used" object being removed from the Map. |
void | readExternal(ObjectInput in) |
protected void | removeLRU()
This method is used internally by the class for
finding and removing the LRU Object. |
void | setMaximumSize(int maximumSize) Setter for property maximumSize. |
void | writeExternal(ObjectOutput out) |
Parameters: i Maximum capacity of the LRUMap
Get the value for a key from the Map. The key will be promoted to the Most Recently Used position. Note that get(Object) operations will modify the underlying Collection. Calling get(Object) inside of an iteration over keys, values, etc. is currently unsupported.
Parameters: key Key to retrieve
Returns: Returns the value. Returns null if the key has a null value or if the key has no value.
Returns: Value of property maximumSize.
Parameters: key key that was removed value value of that key (can be null)
Removes the key and its Object from the Map.
(Note: this may result in the "Least Recently Used" object being removed from the Map. In that case, the removeLRU() method is called. See javadoc for removeLRU() for more details.)
Parameters: key Key of the Object to add. value Object to add
Returns: Former value of the key
Parameters: maximumSize New value of property maximumSize.