de.ipcon.tools

Class WeakIdentityHashMap<K,V>

java.lang.Object

java.util.AbstractMap<K,V>

de.ipcon.tools.WeakIdentityHashMap<K,V>

All Implemented Interfaces:

java.util.Map<K,V>

public class WeakIdentityHashMap<K,V>
extends java.util.AbstractMap<K,V>
implements java.util.Map<K,V>

WeakIdentityHashMap is an implementation of IdentityHashMap with keys which are WeakReferences. A key/value mapping is removed when the key is no longer referenced. All optional operations (adding and removing) are supported. Keys and values can be any objects. Note that the garbage collector acts similar to a second thread on this collection, possibly removing keys.

See Also:

IdentityHashMap, WeakHashMap, WeakReference

Nested Class Summary

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

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

Constructor Summary

Constructors

Constructor and Description
WeakIdentityHashMap() Constructs a new empty WeakIdentityHashMap instance.
WeakIdentityHashMap(int capacity) Constructs a new WeakIdentityHashMap instance with the specified capacity.
WeakIdentityHashMap(int capacity, float loadFactor) Constructs a new WeakIdentityHashMap instance with the specified capacity and load factor.
WeakIdentityHashMap(java.util.Map<? extends K,? extends V> map) Constructs a new WeakIdentityHashMap instance containing the mappings from the specified map.

Method Summary

Modifier and Type	Method and Description
void	cleanup() Force a cleanup by checking the reference queue and removing gc'd entries.
void	clear() Removes all mappings from this map, leaving it empty.
boolean	containsKey(java.lang.Object key) Returns whether this map contains the specified key.
boolean	containsValue(java.lang.Object value) Returns whether this map contains the specified value.
java.util.Set<java.util.Map.Entry<K,V>>	entrySet() Returns a set containing all of the mappings in this map.
V	get(java.lang.Object key) Returns the value of the mapping with the specified key.
boolean	isEmpty()
java.util.Set<K>	keySet() Returns a set of the keys contained in this map.
V	put(K key, V value) Maps the specified key to the specified value.
V	remove(java.lang.Object key) Removes the mapping with the specified key from this map.
int	size()
java.util.Collection<V>	values() Returns a collection of the values contained in this map.

Methods inherited from class java.util.AbstractMap

equals, hashCode, putAll, toString

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Map

compute, computeIfAbsent, computeIfPresent, equals, forEach, getOrDefault, hashCode, merge, putAll, putIfAbsent, remove, replace, replace, replaceAll

Constructor Detail

WeakIdentityHashMap

public WeakIdentityHashMap()

Constructs a new empty WeakIdentityHashMap instance.

WeakIdentityHashMap

public WeakIdentityHashMap(int capacity)

Constructs a new WeakIdentityHashMap instance with the specified capacity.

Parameters:

capacity - the initial capacity of this map.

Throws:

java.lang.IllegalArgumentException - if the capacity is less than zero.

WeakIdentityHashMap

public WeakIdentityHashMap(int capacity,
                           float loadFactor)

Constructs a new WeakIdentityHashMap instance with the specified capacity and load factor.

Parameters:

capacity - the initial capacity of this map.

loadFactor - the initial load factor.

Throws:

java.lang.IllegalArgumentException - if the capacity is less than zero or the load factor is less or equal to zero.

WeakIdentityHashMap

public WeakIdentityHashMap(java.util.Map<? extends K,? extends V> map)

Constructs a new WeakIdentityHashMap instance containing the mappings from the specified map.

Parameters:

map - the mappings to add.

Method Detail

clear

public void clear()

Removes all mappings from this map, leaving it empty.

Specified by:

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

Overrides:

clear in class java.util.AbstractMap<K,V>

See Also:

isEmpty(), size()

containsKey

public boolean containsKey(java.lang.Object key)

Returns whether this map contains the specified key.

Specified by:

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

Overrides:

containsKey in class java.util.AbstractMap<K,V>

Parameters:

key - the key to search for.

Returns:

true if this map contains the specified key, false otherwise.

entrySet

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

Returns a set containing all of the mappings in this map. Each mapping is an instance of Map.Entry. As the set is backed by this map, changes in one will be reflected in the other. It does not support adding operations.

Specified by:

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

Specified by:

entrySet in class java.util.AbstractMap<K,V>

Returns:

a set of the mappings.

keySet

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

Returns a set of the keys contained in this map. The set is backed by this map so changes to one are reflected by the other. The set does not support adding.

Specified by:

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

Overrides:

keySet in class java.util.AbstractMap<K,V>

Returns:

a set of the keys.

values

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

Returns a collection of the values contained in this map. The collection is backed by this map so changes to one are reflected by the other. The collection supports remove, removeAll, retainAll and clear operations, and it does not support add or addAll operations.

This method returns a collection which is the subclass of AbstractCollection. The iterator method of this subclass returns a "wrapper object" over the iterator of map's entrySet(). The size method wraps the map's size method and the contains method wraps the map's containsValue method.

The collection is created when this method is called at first time and returned in response to all subsequent calls. This method may return different Collection when multiple calls to this method, since it has no synchronization performed.

Specified by:

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

Overrides:

values in class java.util.AbstractMap<K,V>

Returns:

a collection of the values contained in this map.

get

public V get(java.lang.Object key)

Returns the value of the mapping with the specified key.

Specified by:

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

Overrides:

get in class java.util.AbstractMap<K,V>

Parameters:

key - the key.

Returns:

the value of the mapping with the specified key, or null if no mapping for the specified key is found.

containsValue

public boolean containsValue(java.lang.Object value)

Returns whether this map contains the specified value.

Specified by:

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

Overrides:

containsValue in class java.util.AbstractMap<K,V>

Parameters:

value - the value to search for.

Returns:

true if this map contains the specified value, false otherwise.

isEmpty

public boolean isEmpty()

Specified by:

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

Overrides:

isEmpty in class java.util.AbstractMap<K,V>

Returns:

true if this map is empty. false otherwise.

cleanup

public void cleanup()

Force a cleanup by checking the reference queue and removing gc'd entries. This method is called occasionally within the API anyways, so depending upon your entries' size, you might ignore it. Otherwise I suggest calling this method once in a while when appropriate.

put

public V put(K key,
             V value)

Maps the specified key to the specified value.

Specified by:

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

Overrides:

put in class java.util.AbstractMap<K,V>

Parameters:

key - the key.

value - the value.

Returns:

the value of any previous mapping with the specified key or null if there was no mapping.

remove

public V remove(java.lang.Object key)

Removes the mapping with the specified key from this map.

Specified by:

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

Overrides:

remove in class java.util.AbstractMap<K,V>

Parameters:

key - the key of the mapping to remove.

Returns:

the value of the removed mapping or null if no mapping for the specified key was found.

size

public int size()

Specified by:

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

Overrides:

size in class java.util.AbstractMap<K,V>

Returns:

the number of elements in this map.