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Added in API level 1

WeakHashMap

public class WeakHashMap
extends AbstractMap<K, V> implements Map<K, V>

java.lang.Object
   ↳ java.util.AbstractMap<K, V>
     ↳ java.util.WeakHashMap<K, V>


WeakHashMap is an implementation of Map 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:

Summary

Public constructors

WeakHashMap()

Constructs a new empty WeakHashMap instance.

WeakHashMap(int capacity)

Constructs a new WeakHashMap instance with the specified capacity.

WeakHashMap(int capacity, float loadFactor)

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

WeakHashMap(Map<? extends K, ? extends V> map)

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

Public methods

void clear()

Removes all mappings from this map, leaving it empty.

boolean containsKey(Object key)

Returns whether this map contains the specified key.

boolean containsValue(Object value)

Returns whether this map contains the specified value.

Set<Entry<K, V>> entrySet()

Returns a set containing all of the mappings in this map.

V get(Object key)

Returns the value of the mapping with the specified key.

boolean isEmpty()

Returns the number of elements in this map.

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.

void putAll(Map<? extends K, ? extends V> map)

Copies all the mappings in the given map to this map.

V remove(Object key)

Removes the mapping with the specified key from this map.

int size()

Returns the number of elements in this map.

Collection<V> values()

Returns a collection of the values contained in this map.

Inherited methods

From class java.util.AbstractMap
From class java.lang.Object
From interface java.util.Map

Public constructors

WeakHashMap

Added in API level 1
WeakHashMap ()

Constructs a new empty WeakHashMap instance.

WeakHashMap

Added in API level 1
WeakHashMap (int capacity)

Constructs a new WeakHashMap instance with the specified capacity.

Parameters
capacity int: the initial capacity of this map.
Throws
IllegalArgumentException if the capacity is less than zero.

WeakHashMap

Added in API level 1
WeakHashMap (int capacity, 
                float loadFactor)

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

Parameters
capacity int: the initial capacity of this map.
loadFactor float: the initial load factor.
Throws
IllegalArgumentException if the capacity is less than zero or the load factor is less or equal to zero.

WeakHashMap

Added in API level 1
WeakHashMap (Map<? extends K, ? extends V> map)

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

Parameters
map Map: the mappings to add.

Public methods

clear

Added in API level 1
void clear ()

Removes all mappings from this map, leaving it empty.

See also:

containsKey

Added in API level 1
boolean containsKey (Object key)

Returns whether this map contains the specified key.

Parameters
key Object: the key to search for.
Returns
boolean true if this map contains the specified key, false otherwise.

containsValue

Added in API level 1
boolean containsValue (Object value)

Returns whether this map contains the specified value.

Parameters
value Object: the value to search for.
Returns
boolean true if this map contains the specified value, false otherwise.

entrySet

Added in API level 1
Set<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.

Returns
Set<Entry<K, V>> a set of the mappings.

get

Added in API level 1
V get (Object key)

Returns the value of the mapping with the specified key.

Parameters
key Object: the key.
Returns
V the value of the mapping with the specified key, or null if no mapping for the specified key is found.

isEmpty

Added in API level 1
boolean isEmpty ()

Returns the number of elements in this map.

Returns
boolean the number of elements in this map.

keySet

Added in API level 1
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.

Returns
Set<K> a set of the keys.

put

Added in API level 1
V put (K key, 
                V value)

Maps the specified key to the specified value.

Parameters
key K: the key.
value V: the value.
Returns
V the value of any previous mapping with the specified key or null if there was no mapping.

putAll

Added in API level 1
void putAll (Map<? extends K, ? extends V> map)

Copies all the mappings in the given map to this map. These mappings will replace all mappings that this map had for any of the keys currently in the given map.

Parameters
map Map: the map to copy mappings from.
Throws
NullPointerException if map is null.

remove

Added in API level 1
V remove (Object key)

Removes the mapping with the specified key from this map.

Parameters
key Object: the key of the mapping to remove.
Returns
V the value of the removed mapping or null if no mapping for the specified key was found.

size

Added in API level 1
int size ()

Returns the number of elements in this map.

Returns
int the number of elements in this map.

values

Added in API level 1
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.

Returns
Collection<V> a collection of the values contained in this map.
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