net.sourceforge.rcache
Class SoftCache<K,V>

java.lang.Object
  java.util.AbstractMap<K,V>
      net.sourceforge.rcache.BaseCache<K,V>
          net.sourceforge.rcache.SoftCache<K,V>

Type Parameters:

K - the type of keys maintained by this cache

V - the type of cached values

All Implemented Interfaces:

java.util.Map<K,V>, Cache<K,V>

public class SoftCache<K,V>
extends BaseCache<K,V>

Memory-Sensitive Cache Based on SoftReferences

Entries in a SoftCache can be garbage collected if, and only if, the JVM considers that more memory is needed. This means that all SoftCache instances will be effectively cleared before an OutOfMemory error is thrown.

For certain applications, this class may be too much memory-consuming. If the programmer only needs to enforce that a single instance is used for a given key, and it is not important to keep this instance afterwards, WeakCache may be a better option.

Author:

Rodrigo Ruiz

See Also:

SoftReference

Nested Class Summary

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

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

Nested classes/interfaces inherited from interface net.sourceforge.rcache.Cache

Cache.Operation

Nested classes/interfaces inherited from interface java.util.Map

java.util.Map.Entry<K,V>

Field Summary

Fields inherited from interface net.sourceforge.rcache.Cache

DEFAULT_CONCURRENCY_LEVEL, DEFAULT_INITIAL_CAPACITY, DEFAULT_LOAD_FACTOR

Constructor Summary

SoftCache()
Default constructor.

SoftCache(int initialCapacity)
Creates an instance with a custom initial capacity.

SoftCache(int initialCapacity, float loadFactor)
Creates an instance with a custom initial capacity and load factor.

SoftCache(int initialCapacity, float loadFactor, int concurrencyLevel)
Creates an instance with custom capacity and concurrency level.

Method Summary

protected KeyedReference<K,V>

createRef(K key, V value, java.lang.ref.ReferenceQueue<V> queue) Factory method for creating a new reference instance.

Methods inherited from class net.sourceforge.rcache.BaseCache

clear, entrySet, equals, get, hashCode, purge, put, remove, size, values

Methods inherited from class java.util.AbstractMap

clone, containsKey, containsValue, isEmpty, keySet, putAll, toString

Methods inherited from class java.lang.Object

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

Constructor Detail

SoftCache

public SoftCache()

Default constructor.

Instances created with this constructor will have a small initial capacity and a highly restricted concurrency level.

For concurrent maps, resizing is a costly operation. Whenever possible, it is advised to specify the expected maximum size, in order to minimise the number of resizes.

SoftCache

public SoftCache(int initialCapacity)

Creates an instance with a custom initial capacity.

Parameters:

initialCapacity - The map initial capacity

SoftCache

public SoftCache(int initialCapacity,
                 float loadFactor)

Creates an instance with a custom initial capacity and load factor.

Parameters:

initialCapacity - The map initial capacity

loadFactor - The map load factor

SoftCache

public SoftCache(int initialCapacity,
                 float loadFactor,
                 int concurrencyLevel)

Creates an instance with custom capacity and concurrency level.

The concurrency level is used as a hint to select the internal Map implementation:

• < 0 : Do not care about concurrency. A HashMap will be used.
• = 0 : No concurrent access allowed. A Hashtable will be selected.
• > 0 : A ConcurrentHashMap will be created with the specified concurrency level.

Parameters:

initialCapacity - The map initial capacity

loadFactor - The map load factor

concurrencyLevel - The concurrency level.

Method Detail

createRef

protected final KeyedReference<K,V> createRef(K key,
                                              V value,
                                              java.lang.ref.ReferenceQueue<V> queue)

Factory method for creating a new reference instance.

Specified by:

createRef in class BaseCache<K,V>

Parameters:

key - The key

value - The value

queue - A reference queue

Returns:

A reference instance containing the key and value