net.sourceforge.jtds.jdbc.cache
Class SimpleLRUCache

java.lang.Object
  java.util.AbstractMap<K,V>
      java.util.HashMap
          net.sourceforge.jtds.jdbc.cache.SimpleLRUCache

All Implemented Interfaces:

java.io.Serializable, java.lang.Cloneable, java.util.Map

public class SimpleLRUCache
extends java.util.HashMap

Simple LRU cache for any type of object. Implemented as an extended HashMap with a maximum size and an aggregated List as LRU queue.

Version:

$Id: SimpleLRUCache.java,v 1.1 2005/04/25 11:46:56 alin_sinpalean Exp $

Author:

Brett Wooldridge

See Also:

Serialized Form

Nested Class Summary

Nested classes/interfaces inherited from class java.util.AbstractMap

java.util.AbstractMap.SimpleEntry<K,V>, java.util.AbstractMap.SimpleImmutableEntry<K,V>

Field Summary

private java.util.LinkedList	list LRU list.
private int	maxCacheSize Maximum cache size.

Constructor Summary

SimpleLRUCache(int maxCacheSize)
Constructs a new LRU cache instance.

Method Summary

void	clear() Overrides clear() to also clear the LRU list.
private void	freshenKey(java.lang.Object key) Moves the specified value to the top of the LRU list (the bottom of the list is where least recently used items live).
java.lang.Object	get(java.lang.Object key) Overrides get() so that it also updates the LRU list.
java.lang.Object	put(java.lang.Object key, java.lang.Object value) Overrides put() so that it also updates the LRU list.
java.lang.Object	remove(java.lang.Object key)

Methods inherited from class java.util.HashMap

clone, containsKey, containsValue, entrySet, isEmpty, keySet, putAll, size, values

Methods inherited from class java.util.AbstractMap

equals, hashCode, toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Map

equals, hashCode

Field Detail

maxCacheSize

private final int maxCacheSize

Maximum cache size.

list

private final java.util.LinkedList list

LRU list.

Constructor Detail

SimpleLRUCache

public SimpleLRUCache(int maxCacheSize)

Constructs a new LRU cache instance.

Parameters:

maxCacheSize - the maximum number of entries in this cache before entries are aged off

Method Detail

clear

public void clear()

Overrides clear() to also clear the LRU list.

Specified by:

clear in interface java.util.Map

Overrides:

clear in class java.util.HashMap

put

public java.lang.Object put(java.lang.Object key,
                            java.lang.Object value)

Overrides put() so that it also updates the LRU list.

Specified by:

put in interface java.util.Map

Overrides:

put in class java.util.HashMap

Parameters:

key - key with which the specified value is to be associated

value - value to be associated with the key

Returns:

previous value associated with key or null if there was no mapping for key; a null return can also indicate that the cache previously associated null with the specified key

See Also:

Map.put(Object, Object)

get

public java.lang.Object get(java.lang.Object key)

Overrides get() so that it also updates the LRU list.

Specified by:

get in interface java.util.Map

Overrides:

get in class java.util.HashMap

Parameters:

key - key with which the expected value is associated

Returns:

the value to which the cache maps the specified key, or null if the map contains no mapping for this key

remove

public java.lang.Object remove(java.lang.Object key)

Specified by:

remove in interface java.util.Map

Overrides:

remove in class java.util.HashMap

See Also:

Map.remove(Object)

freshenKey

private void freshenKey(java.lang.Object key)

Moves the specified value to the top of the LRU list (the bottom of the list is where least recently used items live).

Parameters:

key - key of the value to move to the top of the list