org.apache.mahout.cf.taste.impl.common

Class Cache<K,V>

java.lang.Object

org.apache.mahout.cf.taste.impl.common.Cache<K,V>

All Implemented Interfaces:

Retriever<K,V>

public final class Cache<K,V>
extends Object
implements Retriever<K,V>

An efficient Map-like class which caches values for keys. Values are not "put" into a Cache; instead the caller supplies the instance with an implementation of Retriever which can load the value for a given key.

The cache does not support null keys.

Thanks to Amila Jayasooriya for helping evaluate performance of the rewrite of this class, as part of a Google Summer of Code 2007 project.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	Cache.MatchPredicate<T> Used by {#link #removeKeysMatching(Object)} to decide things that are matching.

Constructor Summary

Constructors

Constructor and Description
Cache(Retriever<? super K,? extends V> retriever) Creates a new cache based on the given Retriever.
Cache(Retriever<? super K,? extends V> retriever, int maxEntries) Creates a new cache based on the given Retriever and with given maximum size.

Method Summary

Modifier and Type	Method and Description
void	clear() Clears the cache.
V	get(K key) Returns cached value for a key.
void	remove(K key) Uncaches any existing value for a given key.
void	removeKeysMatching(Cache.MatchPredicate<K> predicate) Clears all cache entries whose key matches the given predicate.
void	removeValueMatching(Cache.MatchPredicate<V> predicate) Clears all cache entries whose value matches the given predicate.
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

Cache

public Cache(Retriever<? super K,? extends V> retriever)

Creates a new cache based on the given Retriever.

Parameters:

retriever - object which can retrieve values for keys

Cache

public Cache(Retriever<? super K,? extends V> retriever,
             int maxEntries)

Creates a new cache based on the given Retriever and with given maximum size.

Parameters:

retriever - object which can retrieve values for keys

maxEntries - maximum number of entries the cache will store before evicting some

Method Detail

get

public V get(K key)
      throws TasteException

Returns cached value for a key. If it does not exist, it is loaded using a Retriever.

Specified by:

get in interface Retriever<K,V>

Parameters:

key - cache key

Returns:

value for that key

Throws:

TasteException - if an exception occurs while retrieving a new cached value

remove

public void remove(K key)

Uncaches any existing value for a given key.

Parameters:

key - cache key

removeKeysMatching

public void removeKeysMatching(Cache.MatchPredicate<K> predicate)

Clears all cache entries whose key matches the given predicate.

removeValueMatching

public void removeValueMatching(Cache.MatchPredicate<V> predicate)

Clears all cache entries whose value matches the given predicate.

clear

public void clear()

Clears the cache.

toString

public String toString()

Overrides:

toString in class Object