org.apache.commons.collections

Class LRUMap

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) $

Author: James Strachan Morgan Delagrange

Constructor Summary
LRUMap()
Default constructor, primarily for the purpose of de-externalization.
LRUMap(int i)
Create a new LRUMap with a maximum capacity of i.
Method Summary
Objectget(Object key)

Get the value for a key from the Map.

intgetMaximumSize()
Getter for property maximumSize.
protected voidprocessRemovedLRU(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.
Objectput(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.

voidreadExternal(ObjectInput in)
protected voidremoveLRU()
This method is used internally by the class for finding and removing the LRU Object.
voidsetMaximumSize(int maximumSize)
Setter for property maximumSize.
voidwriteExternal(ObjectOutput out)

Constructor Detail

LRUMap

public LRUMap()
Default constructor, primarily for the purpose of de-externalization. This constructors sets a default LRU limit of 100 keys, but this value may be overridden internally as a result of de-externalization.

LRUMap

public LRUMap(int i)
Create a new LRUMap with a maximum capacity of i. Once i capacity is achieved, subsequent gets and puts will push keys out of the map. See .

Parameters: i Maximum capacity of the LRUMap

Method Detail

get

public Object get(Object key)

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.

getMaximumSize

public int getMaximumSize()
Getter for property maximumSize.

Returns: Value of property maximumSize.

processRemovedLRU

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. By default, this method does nothing.

Parameters: key key that was removed value value of that key (can be null)

put

public 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. 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

readExternal

public void readExternal(ObjectInput in)

removeLRU

protected void removeLRU()
This method is used internally by the class for finding and removing the LRU Object.

setMaximumSize

public void setMaximumSize(int maximumSize)
Setter for property maximumSize.

Parameters: maximumSize New value of property maximumSize.

writeExternal

public void writeExternal(ObjectOutput out)
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