jdbm.helper
Class MRU

java.lang.Object
  jdbm.helper.MRU

All Implemented Interfaces:

CachePolicy

public class MRU
extends java.lang.Object
implements CachePolicy

MRU - Most Recently Used cache policy. Methods are *not* synchronized, so no concurrent access is allowed.

Version:

$Id: MRU.java,v 1.8 2005/06/25 23:12:31 doomdark Exp $

Author:

Alex Boisvert

Field Summary

(package private) CacheEntry	_first Beginning of linked-list of cache elements.
(package private) java.util.Hashtable	_hash Cached object hashtable
(package private) CacheEntry	_last End of linked-list of cache elements.
(package private) int	_max Maximum number of objects in the cache.
(package private) java.util.Vector	listeners Cache eviction listeners

Constructor Summary

MRU(int max)
Construct an MRU with a given maximum number of objects.

Method Summary

protected void	addEntry(CacheEntry entry) Add a CacheEntry.
void	addListener(CachePolicyListener listener) Add a listener to this cache policy
java.util.Enumeration	elements() Enumerate elements' values in the cache
java.lang.Object	get(java.lang.Object key) Obtain an object in the cache
protected CacheEntry	purgeEntry() Purge least recently used object from the cache
void	put(java.lang.Object key, java.lang.Object value) Place an object in the cache.
void	remove(java.lang.Object key) Remove an object from the cache
void	removeAll() Remove all objects from the cache
protected void	removeEntry(CacheEntry entry) Remove a CacheEntry from linked list
void	removeListener(CachePolicyListener listener) Remove a listener from this cache policy
protected void	touchEntry(CacheEntry entry) Place entry at the end of linked list -- Most Recently Used

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

_hash

java.util.Hashtable _hash

Cached object hashtable

_max

int _max

Maximum number of objects in the cache.

_first

CacheEntry _first

Beginning of linked-list of cache elements. First entry is element which has been used least recently.

_last

CacheEntry _last

End of linked-list of cache elements. Last entry is element which has been used most recently.

listeners

java.util.Vector listeners

Cache eviction listeners

Constructor Detail

MRU

public MRU(int max)

Construct an MRU with a given maximum number of objects.

Method Detail

put

public void put(java.lang.Object key,
                java.lang.Object value)
         throws CacheEvictionException

Place an object in the cache.

Specified by:

put in interface CachePolicy

Parameters:

key - key for the cached object

value - the cached object

Throws:

CacheEvictionException - propagated if, while evicting objects to make room for new object, an eviction listener encountered this problem.

get

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

Obtain an object in the cache

Specified by:

get in interface CachePolicy

Parameters:

key - key the object was cached under

Returns:

the object if it is still in the cache, null otherwise.

remove

public void remove(java.lang.Object key)

Remove an object from the cache

Specified by:

remove in interface CachePolicy

Parameters:

key - key the object was stored in the cache under.

removeAll

public void removeAll()

Remove all objects from the cache

Specified by:

removeAll in interface CachePolicy

elements

public java.util.Enumeration elements()

Enumerate elements' values in the cache

Specified by:

elements in interface CachePolicy

addListener

public void addListener(CachePolicyListener listener)

Add a listener to this cache policy

Specified by:

addListener in interface CachePolicy

Parameters:

listener - Listener to add to this policy

removeListener

public void removeListener(CachePolicyListener listener)

Remove a listener from this cache policy

Specified by:

removeListener in interface CachePolicy

Parameters:

listener - Listener to remove from this policy

addEntry

protected void addEntry(CacheEntry entry)

Add a CacheEntry. Entry goes at the end of the list.

removeEntry

protected void removeEntry(CacheEntry entry)

Remove a CacheEntry from linked list

touchEntry

protected void touchEntry(CacheEntry entry)

Place entry at the end of linked list -- Most Recently Used

purgeEntry

protected CacheEntry purgeEntry()
                         throws CacheEvictionException

Purge least recently used object from the cache

Returns:

recyclable CacheEntry

Throws:

CacheEvictionException