# WeakHashMap

public class **WeakHashMap** extends [AbstractMap](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html)\<K, V\>  
implements [Map](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html)\<K, V\> Hash table based implementation of the Map interface, with
*weak keys* .
An entry in a WeakHashMap will automatically be removed when
its key is no longer in ordinary use. More precisely, the presence of a
mapping for a given key will not prevent the key from being discarded by the
garbage collector, that is, made finalizable, finalized, and then reclaimed.
When a key has been discarded its entry is effectively removed from the map,
so this class behaves somewhat differently from other Map
implementations.

Both null values and the null key are supported. This class has
performance characteristics similar to those of the HashMap
class, and has the same efficiency parameters of *initial capacity*
and *load factor*.

Like most collection classes, this class is not synchronized.
A synchronized WeakHashMap may be constructed using the
`https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collections.html#synchronizedMap(java.util.Map<K,%20V>)`
method.

This class is intended primarily for use with key objects whose
equals methods test for object identity using the
== operator. Once such a key is discarded it can never be
recreated, so it is impossible to do a lookup of that key in a
WeakHashMap at some later time and be surprised that its entry
has been removed. This class will work perfectly well with key objects
whose equals methods are not based upon object identity, such
as String instances. With such recreatable key objects,
however, the automatic removal of WeakHashMap entries whose
keys have been discarded may prove to be confusing.

The behavior of the WeakHashMap class depends in part upon
the actions of the garbage collector, so several familiar (though not
required) Map invariants do not hold for this class. Because
the garbage collector may discard keys at any time, a
WeakHashMap may behave as though an unknown thread is silently
removing entries. In particular, even if you synchronize on a
WeakHashMap instance and invoke none of its mutator methods, it
is possible for the size method to return smaller values over
time, for the isEmpty method to return false and
then true, for the containsKey method to return
true and later false for a given key, for the
get method to return a value for a given key but later return
null, for the put method to return
null and the remove method to return
false for a key that previously appeared to be in the map, and
for successive examinations of the key set, the value collection, and
the entry set to yield successively smaller numbers of elements.

Each key object in a WeakHashMap is stored indirectly as
the referent of a weak reference. Therefore a key will automatically be
removed only after the weak references to it, both inside and outside of the
map, have been cleared by the garbage collector.

**Implementation note:** The value objects in a
WeakHashMap are held by ordinary strong references. Thus care
should be taken to ensure that value objects do not strongly refer to their
own keys, either directly or indirectly, since that will prevent the keys
from being discarded. Note that a value object may refer indirectly to its
key via the WeakHashMap itself; that is, a value object may
strongly refer to some other key object whose associated value object, in
turn, strongly refers to the key of the first value object. If the values
in the map do not rely on the map holding strong references to them, one way
to deal with this is to wrap values themselves within
WeakReferences before
inserting, as in: m.put(key, new WeakReference(value)),
and then unwrapping upon each get.

The iterators returned by the iterator method of the collections
returned by all of this class's "collection view methods" are
*fail-fast*: if the map is structurally modified at any time after the
iterator is created, in any way except through the iterator's own
remove method, the iterator will throw a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/ConcurrentModificationException.html`. Thus, in the face of concurrent
modification, the iterator fails quickly and cleanly, rather than risking
arbitrary, non-deterministic behavior at an undetermined time in the future.

Note that the fail-fast behavior of an iterator cannot be guaranteed
as it is, generally speaking, impossible to make any hard guarantees in the
presence of unsynchronized concurrent modification. Fail-fast iterators
throw ConcurrentModificationException on a best-effort basis.
Therefore, it would be wrong to write a program that depended on this
exception for its correctness: *the fail-fast behavior of iterators should be used only to detect bugs.*

This class is a member of the
[Java Collections Framework](https://developers.google.com/j2objc/javadoc/jre/technotes/guides/collections/index.html).

##### See Also

- `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/HashMap.html`
- `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ref/WeakReference.html`

### Public Constructor Summary

|---|---|
|   | [WeakHashMap](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#WeakHashMap(int,%20float))(int initialCapacity, float loadFactor) Constructs a new, empty WeakHashMap with the given initial capacity and the given load factor. |
|   | [WeakHashMap](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#WeakHashMap(int))(int initialCapacity) Constructs a new, empty WeakHashMap with the given initial capacity and the default load factor (0.75). |
|   | [WeakHashMap](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#WeakHashMap())() Constructs a new, empty WeakHashMap with the default initial capacity (16) and load factor (0.75). |
|   | [WeakHashMap](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#WeakHashMap(java.util.Map<?%20extends%20K,%20?%20extends%20V>))([Map](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html)\<? extends K, ? extends V\> m) Constructs a new WeakHashMap with the same mappings as the specified map. |

### Public Method Summary

|---|---|
| void | [clear](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#clear())() Removes all of the mappings from this map. |
| boolean | [containsKey](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#containsKey(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key) Returns true if this map contains a mapping for the specified key. |
| boolean | [containsValue](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#containsValue(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) value) Returns true if this map maps one or more keys to the specified value. |
| [Set](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html)\<[Entry](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.Entry.html)\<K, V\>\> | [entrySet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#entrySet())() Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html` view of the mappings contained in this map. |
| void | [forEach](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#forEach(java.util.function.BiConsumer<?%20super%20K,%20?%20super%20V>))([BiConsumer](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiConsumer.html)\<? super K, ? super V\> action) Performs the given action for each entry in this map until all entries have been processed or the action throws an exception. |
| V | [get](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#get(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key) Returns the value to which the specified key is mapped, or `null` if this map contains no mapping for the key. |
| boolean | [isEmpty](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#isEmpty())() Returns true if this map contains no key-value mappings. |
| [Set](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html)\<K\> | [keySet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#keySet())() Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html` view of the keys contained in this map. |
| V | [put](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#put(K,%20V))(K key, V value) Associates the specified value with the specified key in this map. |
| void | [putAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#putAll(java.util.Map<?%20extends%20K,%20?%20extends%20V>))([Map](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html)\<? extends K, ? extends V\> m) Copies all of the mappings from the specified map to this map. |
| V | [remove](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#remove(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key) Removes the mapping for a key from this weak hash map if it is present. |
| void | [replaceAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#replaceAll(java.util.function.BiFunction<?%20super%20K,%20?%20super%20V,%20?%20extends%20V>))([BiFunction](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiFunction.html)\<? super K, ? super V, ? extends V\> function) Replaces each entry's value with the result of invoking the given function on that entry until all entries have been processed or the function throws an exception. |
| int | [size](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#size())() Returns the number of key-value mappings in this map. |
| [Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<V\> | [values](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#values())() Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html` view of the values contained in this map. |

### Inherited Method Summary

From class [java.util.AbstractMap](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html)

|---|---|
| void | [clear](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#clear())() Removes all of the mappings from this map (optional operation). |
| [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) | [clone](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#clone())() Returns a shallow copy of this AbstractMap instance: the keys and values themselves are not cloned. |
| boolean | [containsKey](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#containsKey(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key) Returns `true` if this map contains a mapping for the specified key. |
| boolean | [containsValue](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#containsValue(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) value) Returns `true` if this map maps one or more keys to the specified value. |
| abstract [Set](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html)\<[Entry](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.Entry.html)\<K, V\>\> | [entrySet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#entrySet())() Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html` view of the mappings contained in this map. |
| boolean | [equals](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#equals(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) o) Compares the specified object with this map for equality. |
| V | [get](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#get(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key) Returns the value to which the specified key is mapped, or `null` if this map contains no mapping for the key. |
| int | [hashCode](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#hashCode())() Returns the hash code value for this map. |
| boolean | [isEmpty](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#isEmpty())() Returns `true` if this map contains no key-value mappings. |
| [Set](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html)\<K\> | [keySet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#keySet())() Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html` view of the keys contained in this map. |
| V | [put](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#put(K,%20V))(K key, V value) Associates the specified value with the specified key in this map (optional operation). |
| void | [putAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#putAll(java.util.Map<?%20extends%20K,%20?%20extends%20V>))([Map](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html)\<? extends K, ? extends V\> m) Copies all of the mappings from the specified map to this map (optional operation). |
| V | [remove](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#remove(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key) Removes the mapping for a key from this map if it is present (optional operation). |
| int | [size](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#size())() Returns the number of key-value mappings in this map. |
| [String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) | [toString](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#toString())() Returns a string representation of this map. |
| [Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<V\> | [values](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/AbstractMap.html#values())() Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html` view of the values contained in this map. |

From class [java.lang.Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html)

|---|---|
| [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) | [clone](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#clone())() Creates and returns a copy of this `Object`. |
| boolean | [equals](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#equals(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) obj) Compares this instance with the specified object and indicates if they are equal. |
| void | [finalize](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#finalize())() Invoked when the garbage collector has detected that this instance is no longer reachable. |
| final [Class](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html)\<?\> | [getClass](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#getClass())() Returns the unique instance of `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html` that represents this object's class. |
| int | [hashCode](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#hashCode())() Returns an integer hash code for this object. |
| final void | [notify](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#notify())() Causes a thread which is waiting on this object's monitor (by means of calling one of the `wait()` methods) to be woken up. |
| final void | [notifyAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#notifyAll())() Causes all threads which are waiting on this object's monitor (by means of calling one of the `wait()` methods) to be woken up. |
| [String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) | [toString](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#toString())() Returns a string containing a concise, human-readable description of this object. |
| final void | [wait](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait(long,%20int))(long timeout, int nanos) Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object or until the specified timeout expires. |
| final void | [wait](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait(long))(long timeout) Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object or until the specified timeout expires. |
| final void | [wait](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait())() Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object. |

From interface [java.util.Map](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html)

|---|---|
| abstract void | [clear](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#clear())() Removes all of the mappings from this map (optional operation). |
| V | [compute](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#compute(K,%20java.util.function.BiFunction<?%20super%20K,%20?%20super%20V,%20?%20extends%20V>))(K key, [BiFunction](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiFunction.html)\<? super K, ? super V, ? extends V\> remappingFunction) Attempts to compute a mapping for the specified key and its current mapped value (or `null` if there is no current mapping). |
| V | [computeIfAbsent](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#computeIfAbsent(K,%20java.util.function.Function<?%20super%20K,%20?%20extends%20V>))(K key, [Function](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/Function.html)\<? super K, ? extends V\> mappingFunction) If the specified key is not already associated with a value (or is mapped to `null`), attempts to compute its value using the given mapping function and enters it into this map unless `null`. |
| V | [computeIfPresent](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#computeIfPresent(K,%20java.util.function.BiFunction<?%20super%20K,%20?%20super%20V,%20?%20extends%20V>))(K key, [BiFunction](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiFunction.html)\<? super K, ? super V, ? extends V\> remappingFunction) If the value for the specified key is present and non-null, attempts to compute a new mapping given the key and its current mapped value. |
| abstract boolean | [containsKey](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#containsKey(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key) Returns `true` if this map contains a mapping for the specified key. |
| abstract boolean | [containsValue](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#containsValue(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) value) Returns `true` if this map maps one or more keys to the specified value. |
| abstract [Set](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html)\<[Entry](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.Entry.html)\<K, V\>\> | [entrySet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#entrySet())() Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html` view of the mappings contained in this map. |
| abstract boolean | [equals](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#equals(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) o) Compares the specified object with this map for equality. |
| void | [forEach](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#forEach(java.util.function.BiConsumer<?%20super%20K,%20?%20super%20V>))([BiConsumer](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiConsumer.html)\<? super K, ? super V\> action) Performs the given action for each entry in this map until all entries have been processed or the action throws an exception. |
| abstract V | [get](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#get(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key) Returns the value to which the specified key is mapped, or `null` if this map contains no mapping for the key. |
| V | [getOrDefault](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#getOrDefault(java.lang.Object,%20V))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key, V defaultValue) Returns the value to which the specified key is mapped, or `defaultValue` if this map contains no mapping for the key. |
| abstract int | [hashCode](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#hashCode())() Returns the hash code value for this map. |
| abstract boolean | [isEmpty](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#isEmpty())() Returns `true` if this map contains no key-value mappings. |
| abstract [Set](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html)\<K\> | [keySet](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#keySet())() Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html` view of the keys contained in this map. |
| V | [merge](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#merge(K,%20V,%20java.util.function.BiFunction<?%20super%20V,%20?%20super%20V,%20?%20extends%20V>))(K key, V value, [BiFunction](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiFunction.html)\<? super V, ? super V, ? extends V\> remappingFunction) If the specified key is not already associated with a value or is associated with null, associates it with the given non-null value. |
| abstract V | [put](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#put(K,%20V))(K key, V value) Associates the specified value with the specified key in this map (optional operation). |
| abstract void | [putAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#putAll(java.util.Map<?%20extends%20K,%20?%20extends%20V>))([Map](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html)\<? extends K, ? extends V\> m) Copies all of the mappings from the specified map to this map (optional operation). |
| V | [putIfAbsent](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#putIfAbsent(K,%20V))(K key, V value) If the specified key is not already associated with a value (or is mapped to `null`) associates it with the given value and returns `null`, else returns the current value. |
| boolean | [remove](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#remove(java.lang.Object,%20java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key, [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) value) Removes the entry for the specified key only if it is currently mapped to the specified value. |
| abstract V | [remove](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#remove(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key) Removes the mapping for a key from this map if it is present (optional operation). |
| boolean | [replace](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#replace(K,%20V,%20V))(K key, V oldValue, V newValue) Replaces the entry for the specified key only if currently mapped to the specified value. |
| V | [replace](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#replace(K,%20V))(K key, V value) Replaces the entry for the specified key only if it is currently mapped to some value. |
| void | [replaceAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#replaceAll(java.util.function.BiFunction<?%20super%20K,%20?%20super%20V,%20?%20extends%20V>))([BiFunction](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiFunction.html)\<? super K, ? super V, ? extends V\> function) Replaces each entry's value with the result of invoking the given function on that entry until all entries have been processed or the function throws an exception. |
| abstract int | [size](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#size())() Returns the number of key-value mappings in this map. |
| abstract [Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<V\> | [values](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html#values())() Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html` view of the values contained in this map. |

## Public Constructors

#### public
**WeakHashMap**
(int initialCapacity, float loadFactor)

Constructs a new, empty WeakHashMap with the given initial
capacity and the given load factor.

##### Parameters

| initialCapacity | The initial capacity of the WeakHashMap |
| loadFactor | The load factor of the WeakHashMap |
|---|---|

##### Throws

| [IllegalArgumentException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalArgumentException.html) | if the initial capacity is negative, or if the load factor is nonpositive. |
|---|---|

#### public
**WeakHashMap**
(int initialCapacity)

Constructs a new, empty WeakHashMap with the given initial
capacity and the default load factor (0.75).

##### Parameters

| initialCapacity | The initial capacity of the WeakHashMap |
|---|---|

##### Throws

| [IllegalArgumentException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalArgumentException.html) | if the initial capacity is negative |
|---|---|

#### public
**WeakHashMap**
()

Constructs a new, empty WeakHashMap with the default initial
capacity (16) and load factor (0.75).

#### public
**WeakHashMap**
([Map](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html)\<? extends K, ? extends V\> m)

Constructs a new WeakHashMap with the same mappings as the
specified map. The WeakHashMap is created with the default
load factor (0.75) and an initial capacity sufficient to hold the
mappings in the specified map.

##### Parameters

| m | the map whose mappings are to be placed in this map |
|---|---|

##### Throws

| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if the specified map is null |
|---|---|

## Public Methods

#### public void
**clear**
()

Removes all of the mappings from this map.
The map will be empty after this call returns.

#### public boolean
**containsKey**
([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key)

Returns true if this map contains a mapping for the
specified key.

##### Parameters

| key | The key whose presence in this map is to be tested |
|---|---|

##### Returns

- true if there is a mapping for key; false otherwise

#### public boolean
**containsValue**
([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) value)

Returns true if this map maps one or more keys to the
specified value.

##### Parameters

| value | value whose presence in this map is to be tested |
|---|---|

##### Returns

- true if this map maps one or more keys to the specified value

#### public [Set](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html)\<[Entry](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.Entry.html)\<K, V\>\>
**entrySet**
()

Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html` view of the mappings contained in this map.
The set is backed by the map, so changes to the map are
reflected in the set, and vice-versa. If the map is modified
while an iteration over the set is in progress (except through
the iterator's own remove operation, or through the
setValue operation on a map entry returned by the
iterator) the results of the iteration are undefined. The set
supports element removal, which removes the corresponding
mapping from the map, via the Iterator.remove,
Set.remove, removeAll, retainAll and
clear operations. It does not support the
add or addAll operations.

##### Returns

- a set view of the mappings contained in this map

#### public void
**forEach**
([BiConsumer](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiConsumer.html)\<? super K, ? super V\> action)

Performs the given action for each entry in this map until all entries
have been processed or the action throws an exception. Unless
otherwise specified by the implementing class, actions are performed in
the order of entry set iteration (if an iteration order is specified.)
Exceptions thrown by the action are relayed to the caller.

##### Parameters

| action | The action to be performed for each entry |
|---|---|

#### public V
**get**
([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key)

Returns the value to which the specified key is mapped,
or `null` if this map contains no mapping for the key.

More formally, if this map contains a mapping from a key
`k` to a value `v` such that `(key==null ? k==null :
key.equals(k))`, then this method returns `v`; otherwise
it returns `null`. (There can be at most one such mapping.)

A return value of `null` does not *necessarily*
indicate that the map contains no mapping for the key; it's also
possible that the map explicitly maps the key to `null`.
The `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#containsKey(java.lang.Object)` operation may be used to
distinguish these two cases.

##### Parameters

| key | the key whose associated value is to be returned |
|---|---|

##### Returns

- the value to which the specified key is mapped, or `null` if this map contains no mapping for the key

##### See Also

- `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/WeakHashMap.html#put(K,%20V)`

#### public boolean
**isEmpty**
()

Returns true if this map contains no key-value mappings.
This result is a snapshot, and may not reflect unprocessed
entries that will be removed before next attempted access
because they are no longer referenced.

##### Returns

- `true` if this map contains no key-value mappings

#### public [Set](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html)\<K\>
**keySet**
()

Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Set.html` view of the keys contained in this map.
The set is backed by the map, so changes to the map are
reflected in the set, and vice-versa. If the map is modified
while an iteration over the set is in progress (except through
the iterator's own remove operation), the results of
the iteration are undefined. The set supports element removal,
which removes the corresponding mapping from the map, via the
Iterator.remove, Set.remove,
removeAll, retainAll, and clear
operations. It does not support the add or addAll
operations.

##### Returns

- a set view of the keys contained in this map

#### public V
**put**
(K key, V value)

Associates the specified value with the specified key in this map.
If the map previously contained a mapping for this key, the old
value is replaced.

##### Parameters

| key | key with which the specified value is to be associated. |
| value | value to be associated with the specified key. |
|---|---|

##### Returns

- the previous value associated with key, or null if there was no mapping for key. (A null return can also indicate that the map previously associated null with key.)

#### public void
**putAll**
([Map](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Map.html)\<? extends K, ? extends V\> m)

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

##### Parameters

| m | mappings to be stored in this map. |
|---|---|

##### Throws

| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if the specified map is null. |
|---|---|

#### public V
**remove**
([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) key)

Removes the mapping for a key from this weak hash map if it is present.
More formally, if this map contains a mapping from key k to
value v such that `(key==null ? k==null :
key.equals(k))`, that mapping is removed. (The map can contain
at most one such mapping.)

Returns the value to which this map previously associated the key,
or null if the map contained no mapping for the key. A
return value of null does not *necessarily* indicate
that the map contained no mapping for the key; it's also possible
that the map explicitly mapped the key to null.

The map will not contain a mapping for the specified key once the
call returns.

##### Parameters

| key | key whose mapping is to be removed from the map |
|---|---|

##### Returns

- the previous value associated with key, or null if there was no mapping for key

#### public void
**replaceAll**
([BiFunction](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/function/BiFunction.html)\<? super K, ? super V, ? extends V\> function)

Replaces each entry's value with the result of invoking the given
function on that entry until all entries have been processed or the
function throws an exception. Exceptions thrown by the function are
relayed to the caller.

##### Parameters

| function | the function to apply to each entry |
|---|---|

#### public int
**size**
()

Returns the number of key-value mappings in this map.
This result is a snapshot, and may not reflect unprocessed
entries that will be removed before next attempted access
because they are no longer referenced.

##### Returns

- the number of key-value mappings in this map

#### public [Collection](https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html)\<V\>
**values**
()

Returns a `https://developers.google.com/j2objc/javadoc/jre/reference/java/util/Collection.html` view of the values contained in this map.
The collection is backed by the map, so changes to the map are
reflected in the collection, and vice-versa. If the map is
modified while an iteration over the collection is in progress
(except through the iterator's own remove operation),
the results of the iteration are undefined. The collection
supports element removal, which removes the corresponding
mapping from the map, via the Iterator.remove,
Collection.remove, removeAll,
retainAll and clear operations. It does not
support the add or addAll operations.

##### Returns

- a collection view of the values contained in this map