org.zeroturnaround.javarebel.integration.util

Class WeakIdentityHashMap<K,V>

java.lang.Object

org.zeroturnaround.javarebel.integration.util.WeakIdentityHashMap<K,V>

All Implemented Interfaces:

Map<K,V>

public class WeakIdentityHashMap<K,V>
extends Object
implements Map<K,V>

A hashtable-based Map implementation with weak keys and using reference-equality in place of object-equality when comparing keys (and values). In an WeakIdentityHashMap, two keys k1 and k2 are considered equal if and only if (k1 == k2). An entry in a WeakIdentityHashMap 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.

Based on java.util.WeakHashMap

Version:

1.0

Author:

Dawid Kurzyniec

See Also:

IdentityHashMap, WeakHashMap

Constructor Summary

Constructors

Constructor and Description
WeakIdentityHashMap() Constructs a new, empty WeakIdentityHashMap with the default initial capacity (16) and the default load factor (0.75).
WeakIdentityHashMap(int initialCapacity) Constructs a new, empty WeakIdentityHashMap with the given initial capacity and the default load factor, which is 0.75.
WeakIdentityHashMap(int initialCapacity, float loadFactor) Constructs a new, empty WeakIdentityHashMap with the given initial capacity and the given load factor.
WeakIdentityHashMap(Map<K,V> t) Constructs a new WeakIdentityHashMap with the same mappings as the specified Map.

Method Summary

Modifier and Type	Method and Description
void	clear() Removes all mappings from this map.
boolean	containsKey(Object key) Returns true if this map contains a mapping for the specified key.
boolean	containsValue(Object value) Returns true if this map maps one or more keys to the specified value.
Set	entrySet() Returns a collection view of the mappings contained in this map.
V	get(Object key) Returns the value to which the specified key is mapped in this weak hash map, or null if the map contains no mapping for this key.
boolean	isEmpty() Returns true if this map contains no key-value mappings.
Set<K>	keySet() Returns a set view of the keys contained in this map.
V	put(K key, V value) Associates the specified value with the specified key in this map.
void	putAll(Map<? extends K,? extends V> t) 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.
V	remove(Object key) Removes the mapping for this key from this map if present.
int	size() Returns the number of key-value mappings in this map.
Collection<V>	values() Returns a collection view of the values contained in this map.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface java.util.Map

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

Constructor Detail

WeakIdentityHashMap

public WeakIdentityHashMap(int initialCapacity,
                           float loadFactor)

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

Parameters:

initialCapacity - The initial capacity of the WeakIdentityHashMap

loadFactor - The load factor of the WeakIdentityHashMap

Throws:

IllegalArgumentException - If the initial capacity is negative, or if the load factor is nonpositive.

WeakIdentityHashMap

public WeakIdentityHashMap(int initialCapacity)

Constructs a new, empty WeakIdentityHashMap with the given initial capacity and the default load factor, which is 0.75.

Parameters:

initialCapacity - The initial capacity of the WeakIdentityHashMap

Throws:

IllegalArgumentException - If the initial capacity is negative.

WeakIdentityHashMap

public WeakIdentityHashMap()

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

WeakIdentityHashMap

public WeakIdentityHashMap(Map<K,V> t)

Constructs a new WeakIdentityHashMap with the same mappings as the specified Map. The WeakIdentityHashMap is created with default load factor, which is 0.75 and an initial capacity sufficient to hold the mappings in the specified Map.

Parameters:

t - the map whose mappings are to be placed in this map.

Throws:

NullPointerException - if the specified map is null.

Method Detail

size

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.

Specified by:

size in interface Map<K,V>

isEmpty

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.

Specified by:

isEmpty in interface Map<K,V>

get

public V get(Object key)

Returns the value to which the specified key is mapped in this weak hash map, or null if the map contains no mapping for this key. A return value of null does not necessarily indicate that the map contains no mapping for the key; it is also possible that the map explicitly maps the key to null. The containsKey method may be used to distinguish these two cases.

Specified by:

get in interface Map<K,V>

Parameters:

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

Returns:

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

See Also:

put(Object, Object)

containsKey

public boolean containsKey(Object key)

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

Specified by:

containsKey in interface Map<K,V>

Parameters:

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

Returns:

true if there is a mapping for key; false otherwise

put

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.

Specified by:

put in interface Map<K,V>

Parameters:

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

value - value to be associated with the specified key.

Returns:

previous value associated with specified key, or null if there was no mapping for key. A null return can also indicate that the HashMap previously associated null with the specified key.

putAll

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

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.

Specified by:

putAll in interface Map<K,V>

Parameters:

t - mappings to be stored in this map.

Throws:

NullPointerException - if the specified map is null.

remove

public V remove(Object key)

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

Specified by:

remove in interface Map<K,V>

Parameters:

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

Returns:

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

clear

public void clear()

Removes all mappings from this map.

Specified by:

clear in interface Map<K,V>

containsValue

public boolean containsValue(Object value)

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

Specified by:

containsValue in interface Map<K,V>

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.

keySet

public Set<K> keySet()

Returns a set 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. The set supports element removal, which removes the corresponding mapping from this map, via the Iterator.remove, Set.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.

Specified by:

keySet in interface Map<K,V>

Returns:

a set view of the keys contained in this map.

values

public Collection<V> values()

Returns a collection 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. The collection supports element removal, which removes the corresponding mapping from this map, via the Iterator.remove, Collection.remove, removeAll, retainAll, and clear operations. It does not support the add or addAll operations.

Specified by:

values in interface Map<K,V>

Returns:

a collection view of the values contained in this map.

entrySet

public Set entrySet()

Returns a collection view of the mappings contained in this map. Each element in the returned collection is a Map.Entry. The collection is backed by the map, so changes to the map are reflected in the collection, and vice-versa. 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.

Specified by:

entrySet in interface Map<K,V>

Returns:

a collection view of the mappings contained in this map.

See Also:

Map.Entry