org.josef.util

Class CCache<K,V>

java.lang.Object

org.josef.util.CCache<K,V>

Type Parameters:

K - The Key of the objects to cache.

V - The Value of the objects to cache.

@Status(stage=PRODUCTION,
        unitTests=PARTIAL)
 @Review(by="Kees Schotanus",
        at="2009-09-28")
public class CCache<K,V>
extends Object

A thread-safe LRU (Least Recently Used) cache.
An LRU discards its least recently used objects, effectively keeping the MRU (Most Recently Used) objects in cache.
This cache locates objects with the speed of a Map while maintaining an ordering from Most Recently Used to Least Recently Used. The speed of maintaining the ordering is always the same, no matter what cache size you use.
Before jdk 1.5 this class implemented its own combination of a map and a linked list. But jdk 1.5 has a LinkedHashMap which almost completely creates an LRU cache. This CCache only adds some synchronization and some statistics.

Version:

1.0 $Revision: 6488 $

Author:

Kees Schotanus

See Also:

LinkedHashMap

Constructor Summary

Constructors

Constructor and Description
CCache(int maximumSize) Constructs a cache of the supplied maximumSize.

Method Summary

Modifier and Type	Method and Description
void	add(K key, V value) Adds the supplied key/value pair to the cache.
void	clear() Clears the cache.
boolean	containsKey(K key) Determines whether the cache contains a value corresponding to the supplied key.
V	get(K key) Gets the value corresponding to the supplied key from the cache.
double	getCacheHitRatio() Gets the cache/hit ratio.
String	statisticsToString() Creates a String representation of the statistics of this cache.
String	toString() Creates a String representation of this cache, consisting of all the comma separated keys, within brackets.

Methods inherited from class java.lang.Object

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

Constructor Detail

CCache

public CCache(int maximumSize)

Constructs a cache of the supplied maximumSize.

Parameters:

maximumSize - The maximum size of the cache.

Throws:

IllegalArgumentException - When the supplied maximumSize is less than 2.

Method Detail

add

public void add(K key,
                V value)

Adds the supplied key/value pair to the cache.

Parameters:

key - The key used to store the supplied value.

value - The value to cache.

Throws:

NullPointerException - When either the supplied key or the supplied value is null.

containsKey

public boolean containsKey(K key)

Determines whether the cache contains a value corresponding to the supplied key.
This method is non-intrusive (does not change the cache in any way).

Parameters:

key - Key corresponding to the value to check for existence.

Returns:

boolean True when the cache contains a value corresponding to the supplied key or null when this is not the case.

get

public V get(K key)

Gets the value corresponding to the supplied key from the cache.

Parameters:

key - Key corresponding to the value to get from the cache.

Returns:

Null when no value corresponding to the supplied key exists in the cache else the value from the cache that corresponds to the supplied key is returned.

clear

public void clear()

Clears the cache.
This includes the statistical data.

toString

public String toString()

Creates a String representation of this cache, consisting of all the comma separated keys, within brackets. For example: "[1,2,3]".
The order is from LRU to MRU.

Overrides:

toString in class Object

Returns:

A String representation of this cache.

getCacheHitRatio

public double getCacheHitRatio()

Gets the cache/hit ratio.

Returns:

The cache/hit ratio.

statisticsToString

public String statisticsToString()

Creates a String representation of the statistics of this cache.

Returns:

A String representation of the statistics of this cache.