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Java Source Code / Java Documentation » Library » Apache common Collections » org.apache.commons.collections 
Source Cross Reference  Class Diagram Java Document (Java Doc) 


java.lang.Object
   org.apache.commons.collections.SequencedHashMap
      org.apache.commons.collections.LRUMap

LRUMap
public class LRUMap extends SequencedHashMap implements Externalizable(Code)

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
author:
   Morgan Delagrange



Constructor Summary
public  LRUMap()
     Default constructor, primarily for the purpose of de-externalization.
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.

Method Summary
public  Objectget(Object key)
    

Get the value for a key from the Map.

public  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.
public  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.

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


Constructor Detail
LRUMap
public LRUMap()(Code)
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)(Code)
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)(Code)

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 the value. Returns null if the key has anull value or if the key has no value.



getMaximumSize
public int getMaximumSize()(Code)
Getter for property maximumSize. Value of property maximumSize.



processRemovedLRU
protected void processRemovedLRU(Object key, Object value)(Code)
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
Parameters:
  value - value of that key (can be null)



put
public Object put(Object key, Object value)(Code)

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.
Parameters:
  value - Object to add Former value of the key



readExternal
public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException(Code)



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



setMaximumSize
public void setMaximumSize(int maximumSize)(Code)
Setter for property maximumSize.
Parameters:
  maximumSize - New value of property maximumSize.



writeExternal
public void writeExternal(ObjectOutput out) throws IOException(Code)



Methods inherited from org.apache.commons.collections.SequencedHashMap
public void clear()(Code)(Java Doc)
public Object clone() throws CloneNotSupportedException(Code)(Java Doc)
public boolean containsKey(Object key)(Code)(Java Doc)
public boolean containsValue(Object value)(Code)(Java Doc)
public Set entrySet()(Code)(Java Doc)
public boolean equals(Object obj)(Code)(Java Doc)
public Object get(Object o)(Code)(Java Doc)
public Object get(int index)(Code)(Java Doc)
public Map.Entry getFirst()(Code)(Java Doc)
public Object getFirstKey()(Code)(Java Doc)
public Object getFirstValue()(Code)(Java Doc)
public Map.Entry getLast()(Code)(Java Doc)
public Object getLastKey()(Code)(Java Doc)
public Object getLastValue()(Code)(Java Doc)
public Object getValue(int index)(Code)(Java Doc)
public int hashCode()(Code)(Java Doc)
public int indexOf(Object key)(Code)(Java Doc)
public boolean isEmpty()(Code)(Java Doc)
public Iterator iterator()(Code)(Java Doc)
public Set keySet()(Code)(Java Doc)
public int lastIndexOf(Object key)(Code)(Java Doc)
public Object put(Object key, Object value)(Code)(Java Doc)
public void putAll(Map t)(Code)(Java Doc)
public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException(Code)(Java Doc)
public Object remove(Object key)(Code)(Java Doc)
public Object remove(int index)(Code)(Java Doc)
public List sequence()(Code)(Java Doc)
public int size()(Code)(Java Doc)
public String toString()(Code)(Java Doc)
public Collection values()(Code)(Java Doc)
public void writeExternal(ObjectOutput out) throws IOException(Code)(Java Doc)

Methods inherited from java.lang.Object
native protected Object clone() throws CloneNotSupportedException(Code)(Java Doc)
public boolean equals(Object obj)(Code)(Java Doc)
protected void finalize() throws Throwable(Code)(Java Doc)
final native public Class getClass()(Code)(Java Doc)
native public int hashCode()(Code)(Java Doc)
final native public void notify()(Code)(Java Doc)
final native public void notifyAll()(Code)(Java Doc)
public String toString()(Code)(Java Doc)
final native public void wait(long timeout) throws InterruptedException(Code)(Java Doc)
final public void wait(long timeout, int nanos) throws InterruptedException(Code)(Java Doc)
final public void wait() throws InterruptedException(Code)(Java Doc)

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