org.jivesoftware.smack.util.collections
Class AbstractReferenceMap<K,V>

java.lang.Object
  java.util.AbstractMap<K,V>
      org.jivesoftware.smack.util.collections.AbstractHashedMap<K,V>
          org.jivesoftware.smack.util.collections.AbstractReferenceMap<K,V>

All Implemented Interfaces:

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

Direct Known Subclasses:

ReferenceMap

public abstract class AbstractReferenceMap<K,V>
extends AbstractHashedMap<K,V>

An abstract implementation of a hash-based map that allows the entries to be removed by the garbage collector.

This class implements all the features necessary for a subclass reference hash-based map. Key-value entries are stored in instances of the ReferenceEntry class which can be overridden and replaced. The iterators can similarly be replaced, without the need to replace the KeySet, EntrySet and Values view classes.

Overridable methods are provided to change the default hashing behaviour, and to change how entries are added to and removed from the map. Hopefully, all you need for unusual subclasses is here.

When you construct an AbstractReferenceMap, you can specify what kind of references are used to store the map's keys and values. If non-hard references are used, then the garbage collector can remove mappings if a key or value becomes unreachable, or if the JVM's memory is running low. For information on how the different reference types behave, see Reference.

Different types of references can be specified for keys and values. The keys can be configured to be weak but the values hard, in which case this class will behave like a WeakHashMap. However, you can also specify hard keys and weak values, or any other combination. The default constructor uses hard keys and soft values, providing a memory-sensitive cache.

This Map implementation does not allow null elements. Attempting to add a null key or value to the map will raise a NullPointerException.

All the available iterators can be reset back to the start by casting to ResettableIterator and calling reset().

This implementation is not synchronized. You can use Collections.synchronizedMap(java.util.Map) to provide synchronized access to a ReferenceMap.

Since:

Commons Collections 3.1 (extracted from ReferenceMap in 3.0)

Version:

$Revision: 1.1 $ $Date: 2005/10/11 17:05:32 $

Author:

Paul Jack, Matt Hall, John Watkinson, Stephen Colebourne

See Also:

Reference

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 java.util.Map

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

Field Summary

static int	HARD Constant indicating that hard references should be used
static int	SOFT Constant indicating that soft references should be used
static int	WEAK Constant indicating that weak references should be used

Method Summary

void	clear() Clears this map.
boolean	containsKey(java.lang.Object key) Checks whether the map contains the specified key.
boolean	containsValue(java.lang.Object value) Checks whether the map contains the specified value.
org.jivesoftware.smack.util.collections.AbstractHashedMap.HashEntry<K,V>	createEntry(org.jivesoftware.smack.util.collections.AbstractHashedMap.HashEntry<K,V> next, int hashCode, K key, V value) Creates a ReferenceEntry instead of a HashEntry.
java.util.Set<java.util.Map.Entry<K,V>>	entrySet() Returns a set view of this map's entries.
V	get(java.lang.Object key) Gets the value mapped to the key specified.
boolean	isEmpty() Checks whether the map is currently empty.
java.util.Set<K>	keySet() Returns a set view of this map's keys.
MapIterator<K,V>	mapIterator() Gets a MapIterator over the reference map.
V	put(K key, V value) Puts a key-value mapping into this map.
V	remove(java.lang.Object key) Removes the specified mapping from this map.
int	size() Gets the size of the map.
java.util.Collection<V>	values() Returns a collection view of this map's values.

Methods inherited from class org.jivesoftware.smack.util.collections.AbstractHashedMap

equals, hashCode, putAll, toString

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Field Detail

HARD

public static final int HARD

Constant indicating that hard references should be used

See Also:

Constant Field Values

SOFT

public static final int SOFT

Constant indicating that soft references should be used

See Also:

Constant Field Values

WEAK

public static final int WEAK

Constant indicating that weak references should be used

See Also:

Constant Field Values

Method Detail

size

public int size()

Gets the size of the map.

Specified by:

size in interface java.util.Map<K,V>

Overrides:

size in class AbstractHashedMap<K,V>

Returns:

the size

isEmpty

public boolean isEmpty()

Checks whether the map is currently empty.

Specified by:

isEmpty in interface java.util.Map<K,V>

Overrides:

isEmpty in class AbstractHashedMap<K,V>

Returns:

true if the map is currently size zero

containsKey

public boolean containsKey(java.lang.Object key)

Checks whether the map contains the specified key.

Specified by:

containsKey in interface java.util.Map<K,V>

Overrides:

containsKey in class AbstractHashedMap<K,V>

Parameters:

key - the key to search for

Returns:

true if the map contains the key

containsValue

public boolean containsValue(java.lang.Object value)

Checks whether the map contains the specified value.

Specified by:

containsValue in interface java.util.Map<K,V>

Overrides:

containsValue in class AbstractHashedMap<K,V>

Parameters:

value - the value to search for

Returns:

true if the map contains the value

get

public V get(java.lang.Object key)

Gets the value mapped to the key specified.

Specified by:

get in interface java.util.Map<K,V>

Overrides:

get in class AbstractHashedMap<K,V>

Parameters:

key - the key

Returns:

the mapped value, null if no match

put

public V put(K key,
             V value)

Puts a key-value mapping into this map. Neither the key nor the value may be null.

Specified by:

put in interface java.util.Map<K,V>

Overrides:

put in class AbstractHashedMap<K,V>

Parameters:

key - the key to add, must not be null

value - the value to add, must not be null

Returns:

the value previously mapped to this key, null if none

Throws:

java.lang.NullPointerException - if either the key or value is null

remove

public V remove(java.lang.Object key)

Removes the specified mapping from this map.

Specified by:

remove in interface java.util.Map<K,V>

Overrides:

remove in class AbstractHashedMap<K,V>

Parameters:

key - the mapping to remove

Returns:

the value mapped to the removed key, null if key not in map

clear

public void clear()

Clears this map.

Specified by:

clear in interface java.util.Map<K,V>

Overrides:

clear in class AbstractHashedMap<K,V>

mapIterator

public MapIterator<K,V> mapIterator()

Gets a MapIterator over the reference map. The iterator only returns valid key/value pairs.

Specified by:

mapIterator in interface IterableMap<K,V>

Overrides:

mapIterator in class AbstractHashedMap<K,V>

Returns:

a map iterator

entrySet

public java.util.Set<java.util.Map.Entry<K,V>> entrySet()

Returns a set view of this map's entries. An iterator returned entry is valid until next() is called again. The setValue() method on the toArray entries has no effect.

Specified by:

entrySet in interface java.util.Map<K,V>

Overrides:

entrySet in class AbstractHashedMap<K,V>

Returns:

a set view of this map's entries

keySet

public java.util.Set<K> keySet()

Returns a set view of this map's keys.

Specified by:

keySet in interface java.util.Map<K,V>

Overrides:

keySet in class AbstractHashedMap<K,V>

Returns:

a set view of this map's keys

values

public java.util.Collection<V> values()

Returns a collection view of this map's values.

Specified by:

values in interface java.util.Map<K,V>

Overrides:

values in class AbstractHashedMap<K,V>

Returns:

a set view of this map's values

createEntry

public org.jivesoftware.smack.util.collections.AbstractHashedMap.HashEntry<K,V> createEntry(org.jivesoftware.smack.util.collections.AbstractHashedMap.HashEntry<K,V> next,
                                                                                            int hashCode,
                                                                                            K key,
                                                                                            V value)

Creates a ReferenceEntry instead of a HashEntry.

Parameters:

next - the next entry in sequence

hashCode - the hash code to use

key - the key to store

value - the value to store

Returns:

the newly created entry