org.egothor.cache.lfu

Class LfuCache<K,V>

java.lang.Object

org.egothor.cache.AbstractCache<K,V>

org.egothor.cache.lfu.LfuCache<K,V>

Type Parameters:

K - type of the key

V - type of the value

All Implemented Interfaces:

Cache<K,V>

public class LfuCache<K,V>
extends AbstractCache<K,V>

Implementation of Cache that uses the LFU algorithm as an eviction policy.

Field Summary

Fields inherited from class org.egothor.cache.AbstractCache

DEFAULT_CAPACITY

Constructor Summary

Constructors

Constructor and Description
LfuCache() Constructor for the LfuCache object.
LfuCache(int capacity) Constructor for the LfuCache object.
LfuCache(Resolver<K,V> resolver) Constructor for the LfuCache object.
LfuCache(Resolver<K,V> resolver, int capacity) Constructor for the LfuCache object.

Method Summary

Modifier and Type	Method and Description
void	clear() Removes all key-value mappings from the cache and cleans all queues.
boolean	containsKey(K key) Checks whether the specified key is cached.
void	evict() Removes the least frequent key from the cache.
V	get(K key) Gets the value associated with the specified key from the cache if a mapping exists, or the value returned by the resolver.
Set<K>	keySet() Gets all keys contained in the cache.
K	nextEvicted() Gets the least frequent key from the cache.
V	put(K key, V value) Adds a new key-value mapping to the cache.
V	remove(K key) Removes the specified key and its value from the cache.
int	size() Returns the number of key-value mappings in the cache.
String	toString() Returns a text representation of the cache.
V	update(K key, V value) Updates the value associated with the specified key in the cache if a mapping exists for the key.

Methods inherited from class org.egothor.cache.AbstractCache

capacity, getResolver, hitRatio, hits, misses, requests, resetCounters, setResolver

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

LfuCache

public LfuCache()

Constructor for the LfuCache object. Capacity is set to default and resolver always returns null.

LfuCache

public LfuCache(int capacity)

Constructor for the LfuCache object. Resolver always returns null.

Parameters:

capacity - capacity of the cache

LfuCache

public LfuCache(Resolver<K,V> resolver)

Constructor for the LfuCache object. Capacity is set to default.

Parameters:

resolver - resolver to associate with the cache

LfuCache

public LfuCache(Resolver<K,V> resolver,
                int capacity)

Constructor for the LfuCache object.

Parameters:

resolver - resolver to associate with the cache

capacity - capacity of the cache

Method Detail

put

public V put(K key,
             V value)

Adds a new key-value mapping to the cache. If a mapping previously existed for the specified key, it is removed at first. If the cache is full, the least frequent key is removed from the cache.

Specified by:

put in interface Cache<K,V>

Overrides:

put in class AbstractCache<K,V>

Parameters:

key - key to add to the cache

value - value to map the key on

Returns:

previous value associated with the key or null if a previous mapping did not exists in the cache for the specified key

get

public V get(K key)

Gets the value associated with the specified key from the cache if a mapping exists, or the value returned by the resolver.

Specified by:

get in interface Cache<K,V>

Overrides:

get in class AbstractCache<K,V>

Parameters:

key - key to get the value for

Returns:

value associated with the key from the cache, or from the resolver if a mapping does not exits in the cache

remove

public V remove(K key)

Removes the specified key and its value from the cache.

Specified by:

remove in interface Cache<K,V>

Overrides:

remove in class AbstractCache<K,V>

Parameters:

key - key to remove from the cache.

Returns:

value associated with the key, or null if a mapping did not exist

update

public V update(K key,
                V value)

Updates the value associated with the specified key in the cache if a mapping exists for the key.

Specified by:

update in interface Cache<K,V>

Overrides:

update in class AbstractCache<K,V>

Parameters:

key - key to change the value for

value - new value associated with the key

Returns:

previous associated value or null if the key is not cached

containsKey

public boolean containsKey(K key)

Checks whether the specified key is cached.

Specified by:

containsKey in interface Cache<K,V>

Specified by:

containsKey in class AbstractCache<K,V>

Parameters:

key - key to check

Returns:

true, if the key is currently cached, false otherwise

clear

public void clear()

Removes all key-value mappings from the cache and cleans all queues.

keySet

public Set<K> keySet()

Gets all keys contained in the cache.

Returns:

Set of keys contained in the cache.

size

public int size()

Returns the number of key-value mappings in the cache.

Specified by:

size in interface Cache<K,V>

Specified by:

size in class AbstractCache<K,V>

Returns:

number of key-value mappings in the cache

nextEvicted

public K nextEvicted()

Gets the least frequent key from the cache.

Specified by:

nextEvicted in interface Cache<K,V>

Specified by:

nextEvicted in class AbstractCache<K,V>

Returns:

the least frequent key

evict

public void evict()

Removes the least frequent key from the cache.

Specified by:

evict in interface Cache<K,V>

Specified by:

evict in class AbstractCache<K,V>

toString

public String toString()

Returns a text representation of the cache.

Specified by:

toString in class AbstractCache<K,V>

Returns:

text representation of the cache