LibreOffice 24.8.4 · com.sun.star.lib.util.WeakMap · APIdia, the JavaDoc alternative

A hash map that holds values of type WeakReference.

Like HashMap, this implementation provides all of the optional map operations, and permits the null key.

Also like HashMap, this implementation is not synchronized. If multiple threads share an instance, and at least one of them executes any modifying operations on the WeakMap, they have to use external synchronization.

Unlike other map implementations, WeakMap is asymmetric in that put expects the given value to be a plain object that is then wrapped in a WeakReference, while the occurrences of values in all other methods (containsValue, entrySet, equals, get, hashCode, remove, values, and also the return value of put) expect already wrapped instances of WeakReference. That is, after weakMap.put("key", o), weakMap.get("key").equals(o) does not work as naïvely expected; neither does weakMap1.putAll(weakMap2).

At an arbitrary time after the WeakReference value of an entry has been cleared by the garbage collector, the entry is automatically removed from the map.

Values placed into a WeakMap may optionally support the DisposeNotifier interface. For those that do, the associated WeakReference wrappers are automatically cleared as soon as the values are disposed.

Note that this class does not actually implement the Map interface properly, the type of the return value of the entrySet and values methods is wrong, but the "implements Map" is retained for backward compatibility.

Nested and Inner Type Summary

Modifier and Type	Class and Description
private static class	WeakMap.Entry<K, V>

Field Summary

Modifier and Type	Field and Description
private final HashMap<K, WeakReference<V>>	map Declare the map as WeakReference instead of Entry because it makes the return type signatures of values() and keySet() cleaner.
private final ReferenceQueue<V>	queue

Constructor Summary

Access	Constructor and Description
public	WeakMap() Constructs an empty `WeakMap`.
public	WeakMap(Map<K, V> the map whose mappings are to be placed in this map m) Constructs a new `WeakMap` with the same mappings as the specified `Map`.

Method Summary

Modifier and Type	Method and Description
private void	cleanUp() cleanUp() must only be called from within modifying methods.
public void	clear() Implements java.util.Map.clear. Removes all mappings from this map.
public boolean	Returns: `true` if this map contains a mapping for the specified key containsKey(Object the key whose presence in this map is to be tested key) Implements java.util.Map.containsKey. Returns `true` if this map contains a mapping for the specified key.
public boolean	Returns: `true` if this map maps one or more keys to the specified value containsValue(Object the value whose presence in this map is to be tested value) Implements java.util.Map.containsValue. Returns `true` if this map maps one or more keys to the specified value.
public Set<E>	Returns: a collection view of the mappings contained in this map entrySet() Implements java.util.Map.entrySet. Returns a collection view of the mappings contained in this map.
public boolean	equals(Object o) Overrides java.lang.Object.equals. Implements java.util.Map.equals. Compares the specified object with this map for equality.
public WeakReference<V>	Returns: the value to which this map maps the specified key, or `null` if the map contains no mapping for this key get(Object the key whose associated value is to be returned key) Implements java.util.Map.get. Returns the value to which the specified key is mapped in this map, or `null` if the map contains no mapping for this key.
public static <T> T	Returns: the referent of the specified `WeakReference`, or `null` if `ref` is `null` getValue(Object must be either an instance of `WeakReference` or `null` ref) Returns the referent of a `WeakReference`, silently handling a `null` argument.
public int	hashCode() Overrides java.lang.Object.hashCode. Implements java.util.Map.hashCode. Returns the hash code value for this map.
public boolean	Returns: `true` if this map contains no key–value mappings isEmpty() Implements java.util.Map.isEmpty. Returns `true` if this map contains no key–value mappings.
public Set<K>	Returns: a set view of the keys contained in this map keySet() Implements java.util.Map.keySet. Returns a view of the keys contained in this map.
public Object	Returns: previous value associated with the specified key, or `null` if there was no mapping for the key put(Object the key with which the specified value is to be associated key, Object the value to be associated with the specified key. This must be a plain object, which is then wrapped in a `WeakReference`. value) Implements java.util.Map.put. Associates the specified value with the specified key in this map.
public void	putAll(Map<K, V> mappings to be stored in this map. The values of those mappings must be plain objects, which are then wrapped in instances of `WeakReference`. m) Implements java.util.Map.putAll. Copies all of the mappings from the specified map to this map.
public Object	Returns: previous value associated with the specified key, or `null` if there was no mapping for the key remove(Object the key whose mapping is to be removed from the map key) Implements java.util.Map.remove. Removes the mapping for this key from this map if present.
public int	Returns: the number of key–value mappings in this map size() Implements java.util.Map.size. Returns the number of key–value mappings in this map.
public Collection<WeakReference<V>>	Returns: a collection view of the values contained in this map values() Implements java.util.Map.values. Returns a collection view of the values contained in this map.

Inherited from java.lang.Object:: clone finalize getClass notify notifyAll toString wait wait wait

Field Detail

map	back to summary
private final HashMap<K, WeakReference<V>> map Declare the map as WeakReference instead of Entry because it makes the return type signatures of values() and keySet() cleaner.

queue	back to summary
private final ReferenceQueue<V> queue

Constructor Detail

WeakMap	back to summary
public WeakMap() Constructs an empty `WeakMap`.

WeakMap back to summary

WeakMap	back to summary
public WeakMap(Map<K, V> m) Constructs a new `WeakMap` with the same mappings as the specified `Map`. Parameters m:Map<K, V> the map whose mappings are to be placed in this map

public WeakMap(Map<K, V> m)

Constructs a new WeakMap with the same mappings as the specified Map.

Parameters

m:Map<K, V>: the map whose mappings are to be placed in this map

Method Detail

cleanUp	back to summary
private void cleanUp() cleanUp() must only be called from within modifying methods. Otherwise, the implementations of entrySet, keySet and values would break (Specifically, iterating over the collections returned by those methods), as non-modifying methods might modify the underlying map. Annotations @SuppressWarnings:unchecked

cleanUp

back to summary

private void cleanUp()

cleanUp() must only be called from within modifying methods. Otherwise, the implementations of entrySet, keySet and values would break (Specifically, iterating over the collections returned by those methods), as non-modifying methods might modify the underlying map.

Annotations

@SuppressWarnings:unchecked

clear	back to summary
public void clear() Implements java.util.Map.clear. Removes all mappings from this map. This is a modifying operation.

clear

back to summary

public void clear()

Implements java.util.Map.clear.

Removes all mappings from this map.

This is a modifying operation.

containsKey back to summary

containsKey	back to summary
public boolean containsKey(Object key) Implements java.util.Map.containsKey. Returns `true` if this map contains a mapping for the specified key. This is a non-modifying operation. Parameters key:Object the key whose presence in this map is to be tested Returns:boolean `true` if this map contains a mapping for the specified key

public boolean containsKey(Object key)

Implements java.util.Map.containsKey.

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

This is a non-modifying operation.

Parameters

key:Object: the key whose presence in this map is to be tested

Returns:boolean

true if this map contains a mapping for the specified key

containsValue back to summary

containsValue	back to summary
public boolean containsValue(Object value) Implements java.util.Map.containsValue. Returns `true` if this map maps one or more keys to the specified value. This is a non-modifying operation. Parameters value:Object the value whose presence in this map is to be tested Returns:boolean `true` if this map maps one or more keys to the specified value

public boolean containsValue(Object value)

Implements java.util.Map.containsValue.

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

This is a non-modifying operation.

Parameters

value:Object: the value whose presence in this map is to be tested

Returns:boolean

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

entrySet	back to summary
public Set<E> entrySet() Implements java.util.Map.entrySet. Returns a collection view of the mappings contained in this map. This is a non-modifying operation. Returns:Set<E> a collection view of the mappings contained in this map

entrySet

back to summary

public Set<E> entrySet()

Implements java.util.Map.entrySet.

Returns a collection view of the mappings contained in this map.

This is a non-modifying operation.

Returns:Set<E>: a collection view of the mappings contained in this map

equals back to summary

equals	back to summary
public boolean equals(Object o) Overrides java.lang.Object.equals. Implements java.util.Map.equals. Doc from java.util.Map.equals. Compares the specified object with this map for equality. Returns `true` if the given object is also a map and the two maps represent the same mappings. More formally, two maps `m1` and `m2` represent the same mappings if `m1.entrySet().equals(m2.entrySet())`. This ensures that the `equals` method works properly across different implementations of the `Map` interface. Annotations @Override

public boolean equals(Object o)

Overrides java.lang.Object.equals.

Implements java.util.Map.equals.

Doc from java.util.Map.equals.

Compares the specified object with this map for equality. Returns true if the given object is also a map and the two maps represent the same mappings. More formally, two maps m1 and m2 represent the same mappings if m1.entrySet().equals(m2.entrySet()). This ensures that the equals method works properly across different implementations of the Map interface.

Annotations

@Override

get back to summary

get	back to summary
public WeakReference<V> get(Object key) Implements java.util.Map.get. Returns the value to which the specified key is mapped in this map, or `null` if the map contains no mapping for this key. This is a non-modifying operation. Parameters key:Object the key whose associated value is to be returned Returns:WeakReference<V> the value to which this map maps the specified key, or `null` if the map contains no mapping for this key

public WeakReference<V> get(Object key)

Implements java.util.Map.get.

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

This is a non-modifying operation.

Parameters

key:Object: the key whose associated value is to be returned

Returns:WeakReference<V>

the value to which this map maps the specified key, or null if the map contains no mapping for this key

getValue back to summary

getValue	back to summary
public static <T> T getValue(Object ref) Returns the referent of a `WeakReference`, silently handling a `null` argument. This static method is useful to wrap around the return values of methods like `get`. Parameters ref:Object must be either an instance of `WeakReference` or `null` Returns:T the referent of the specified `WeakReference`, or `null` if `ref` is `null` Annotations @SuppressWarnings:unchecked

public static <T> T getValue(Object ref)

Returns the referent of a WeakReference, silently handling a null argument.

This static method is useful to wrap around the return values of methods like get.

Parameters

ref:Object: must be either an instance of WeakReference or null

Returns:T

the referent of the specified WeakReference, or null if ref is null

Annotations

@SuppressWarnings:unchecked

hashCode back to summary

hashCode	back to summary
public int hashCode() Overrides java.lang.Object.hashCode. Implements java.util.Map.hashCode. Doc from java.util.Map.hashCode. Returns the hash code value for this map. The hash code of a map is defined to be the sum of the hash codes of each entry in the map's `entrySet()` view. This ensures that `m1.equals(m2)` implies that `m1.hashCode()==m2.hashCode()` for any two maps `m1` and `m2`, as required by the general contract of `Object#hashCode`. Annotations @Override

public int hashCode()

Overrides java.lang.Object.hashCode.

Implements java.util.Map.hashCode.

Doc from java.util.Map.hashCode.

Returns the hash code value for this map. The hash code of a map is defined to be the sum of the hash codes of each entry in the map's entrySet() view. This ensures that m1.equals(m2) implies that m1.hashCode()==m2.hashCode() for any two maps m1 and m2, as required by the general contract of Object#hashCode.

Annotations

@Override

isEmpty back to summary

isEmpty	back to summary
public boolean isEmpty() Implements java.util.Map.isEmpty. Returns `true` if this map contains no key–value mappings. This is a non-modifying operation. Returns:boolean `true` if this map contains no key–value mappings

public boolean isEmpty()

Implements java.util.Map.isEmpty.

Returns true if this map contains no key–value mappings.

This is a non-modifying operation.

Returns:boolean: true if this map contains no key–value mappings

keySet	back to summary
public Set<K> keySet() Implements java.util.Map.keySet. Returns a view of the keys contained in this map. This is a non-modifying operation. Returns:Set<K> a set view of the keys contained in this map

keySet

back to summary

public Set<K> keySet()

Implements java.util.Map.keySet.

Returns a view of the keys contained in this map.

This is a non-modifying operation.

Returns:Set<K>: a set view of the keys contained in this map

put back to summary

put	back to summary
public Object put(Object key, Object value) Implements java.util.Map.put. Associates the specified value with the specified key in this map. This is a modifying operation. Parameters key:Object the key with which the specified value is to be associated value:Object the value to be associated with the specified key. This must be a plain object, which is then wrapped in a `WeakReference`. Returns:Object previous value associated with the specified key, or `null` if there was no mapping for the key Annotations @SuppressWarnings:unchecked

public Object put(Object key, Object value)

Implements java.util.Map.put.

Associates the specified value with the specified key in this map.

This is a modifying operation.

Parameters

key:Object: the key with which the specified value is to be associated
value:Object: the value to be associated with the specified key. This must be a plain object, which is then wrapped in a WeakReference.

Returns:Object

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

Annotations

@SuppressWarnings:unchecked

putAll back to summary

putAll	back to summary
public void putAll(Map<K, V> m) Implements java.util.Map.putAll. Copies all of the mappings from the specified map to this map. This is a modifying operation. Parameters m:Map<K, V> mappings to be stored in this map. The values of those mappings must be plain objects, which are then wrapped in instances of `WeakReference`. Annotations @SuppressWarnings:unchecked

public void putAll(Map<K, V> m)

Implements java.util.Map.putAll.

Copies all of the mappings from the specified map to this map.

This is a modifying operation.

Parameters

m:Map<K, V>: mappings to be stored in this map. The values of those mappings must be plain objects, which are then wrapped in instances of WeakReference.

Annotations

@SuppressWarnings:unchecked

remove back to summary

remove	back to summary
public Object remove(Object key) Implements java.util.Map.remove. Removes the mapping for this key from this map if present. This is a modifying operation. Parameters key:Object the key whose mapping is to be removed from the map Returns:Object previous value associated with the specified key, or `null` if there was no mapping for the key

public Object remove(Object key)

Implements java.util.Map.remove.

Removes the mapping for this key from this map if present.

This is a modifying operation.

Parameters

key:Object: the key whose mapping is to be removed from the map

Returns:Object

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

size	back to summary
public int size() Implements java.util.Map.size. Returns the number of key–value mappings in this map. This is a non-modifying operation. Returns:int the number of key–value mappings in this map

size

back to summary

public int size()

Implements java.util.Map.size.

Returns the number of key–value mappings in this map.

This is a non-modifying operation.

Returns:int: the number of key–value mappings in this map

values	back to summary
public Collection<WeakReference<V>> values() Implements java.util.Map.values. Returns a collection view of the values contained in this map. This is a non-modifying operation. Returns:Collection<WeakReference<V>> a collection view of the values contained in this map

values

back to summary

public Collection<WeakReference<V>> values()

Implements java.util.Map.values.

Returns a collection view of the values contained in this map.

This is a non-modifying operation.

Returns:Collection<WeakReference<V>>: a collection view of the values contained in this map

public final Class WeakMap<K, V>

Nested and Inner Type Summary

Field Summary

Constructor Summary

Method Summary

Field Detail

Constructor Detail

Method Detail

private final Class WeakMap.Entry<K, V>

Field Summary

Constructor Summary

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Field Detail

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Method Detail