org.apache.directory.shared.util

Class SynchronizedLRUMap

java.lang.Object

org.apache.directory.shared.util.SequencedHashMap

org.apache.directory.shared.util.SynchronizedLRUMap

All Implemented Interfaces:

Externalizable, Serializable, Cloneable, Map

public final class SynchronizedLRUMap
extends SequencedHashMap
implements Externalizable

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

Author:

Apache Directory Project

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
SynchronizedLRUMap() Default constructor, primarily for the purpose of de-externalization.
SynchronizedLRUMap(int i) Create a new LRUMap with a maximum capacity of i.

Method Summary

Methods

Modifier and Type	Method and Description
Object	get(Object key) Get the value for a key from the Map.
int	getMaximumSize() Getter for property maximumSize.
Object	put(Object key, Object value) Removes the key and its Object from the Map.
void	setMaximumSize(int maximumSize) Setter for property maximumSize.

Methods inherited from class org.apache.directory.shared.util.SequencedHashMap

clear, clone, containsKey, containsValue, entrySet, equals, get, getFirst, getFirstKey, getFirstValue, getLast, getLastKey, getLastValue, getValue, hashCode, indexOf, isEmpty, iterator, keySet, lastIndexOf, putAll, readExternal, remove, remove, sequence, size, toString, values, writeExternal

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.io.Externalizable

readExternal, writeExternal

Constructor Detail

SynchronizedLRUMap

public SynchronizedLRUMap()

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.

SynchronizedLRUMap

public SynchronizedLRUMap(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.

Specified by:

get in interface Map

Overrides:

get in class SequencedHashMap

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.

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.)

Specified by:

put in interface Map

Overrides:

put in class SequencedHashMap

Parameters:

key - Key of the Object to add.

value - Object to add

Returns:

Former value of the key

getMaximumSize

public int getMaximumSize()

Getter for property maximumSize.

Returns:

Value of property maximumSize.

setMaximumSize

public void setMaximumSize(int maximumSize)

Setter for property maximumSize.

Parameters:

maximumSize - New value of property maximumSize.