java.util
Class IdentityHashMap<K,V>

java.lang.Object
  java.util.AbstractMap<K,V>
      java.util.IdentityHashMap<K,V>

All Implemented Interfaces:

Serializable, Cloneable, Map<K,V>

public class IdentityHashMap<K,V>
extends AbstractMap<K,V>
implements Map<K,V>, Serializable, Cloneable

IdentityHashMap This is a variant on HashMap which tests equality by reference instead of by value. Basically, keys and values are compared for equality by checking if their references are equal rather than by calling the "equals" function. IdentityHashMap uses open addressing (linear probing in particular) for collision resolution. This is different from HashMap which uses Chaining. Like HashMap, IdentityHashMap is not thread safe, so access by multiple threads must be synchronized by an external mechanism such as Collections.synchronizedMap.

Since:

1.4

See Also:

Serialized Form

Nested Class Summary

(package private) static class	IdentityHashMap.IdentityHashMapEntry<K,V>
(package private) static class	IdentityHashMap.IdentityHashMapEntrySet<KT,VT>
(package private) static class	IdentityHashMap.IdentityHashMapIterator<E,KT,VT>

Nested classes/interfaces inherited from interface java.util.Map

Map.Entry<K,V>

Field Summary

(package private) Object[]	elementData
(package private) int	modCount
(package private) int	size
(package private) int	threshold

Fields inherited from class java.util.AbstractMap

keySet, valuesCollection

Constructor Summary

IdentityHashMap()
Create an IdentityHashMap with default maximum size

IdentityHashMap(int maxSize)
Create an IdentityHashMap with the given maximum size parameter

IdentityHashMap(Map<? extends K,? extends V> map)
Create an IdentityHashMap using the given Map as initial values.

Method Summary

void	clear() Removes all elements from this Map, leaving it empty.
Object	clone() Returns a new IdentityHashMap with the same mappings and size as this one.
boolean	containsKey(Object key) Searches this Map for the specified key.
boolean	containsValue(Object value) Searches this Map for the specified value.
Set<Map.Entry<K,V>>	entrySet() Returns a Set of the mappings contained in this IdentityHashMap.
boolean	equals(Object object) Compares this map with other objects.
V	get(Object key) Returns the value of the mapping with the specified key.
boolean	isEmpty() Returns if this IdentityHashMap has no elements, a size of zero.
Set<K>	keySet() Returns a Set of the keys contained in this IdentityHashMap.
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 a mapping with the specified key from this IdentityHashMap.
int	size() Returns the number of mappings in this IdentityHashMap.
Collection<V>	values() Returns a Collection of the values contained in this IdentityHashMap.

Methods inherited from class java.util.AbstractMap

hashCode, toString

Methods inherited from class java.lang.Object

finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Map

hashCode

Field Detail

elementData

transient Object[] elementData

size

int size

threshold

transient int threshold

modCount

transient int modCount

Constructor Detail

IdentityHashMap

public IdentityHashMap()

Create an IdentityHashMap with default maximum size

IdentityHashMap

public IdentityHashMap(int maxSize)

Create an IdentityHashMap with the given maximum size parameter

Parameters:

maxSize - The estimated maximum number of entries that will be put in this map.

IdentityHashMap

public IdentityHashMap(Map<? extends K,? extends V> map)

Create an IdentityHashMap using the given Map as initial values.

Parameters:

map - A map of (key,value) pairs to copy into the IdentityHashMap

Method Detail

clear

public void clear()

Removes all elements from this Map, leaving it empty.

Specified by:

clear in interface Map<K,V>

Overrides:

clear in class AbstractMap<K,V>

Throws:

UnsupportedOperationException - when removing from this Map is not supported

See Also:

isEmpty(), size

containsKey

public boolean containsKey(Object key)

Searches this Map for the specified key.

Specified by:

containsKey in interface Map<K,V>

Overrides:

containsKey in class AbstractMap<K,V>

Parameters:

key - the object to search for

Returns:

true if key is a key of this Map, false otherwise

containsValue

public boolean containsValue(Object value)

Searches this Map for the specified value.

Specified by:

containsValue in interface Map<K,V>

Overrides:

containsValue in class AbstractMap<K,V>

Parameters:

value - the object to search for

Returns:

true if value is a value of this Map, false otherwise

get

public V get(Object key)

Returns the value of the mapping with the specified key.

Specified by:

get in interface Map<K,V>

Overrides:

get in class AbstractMap<K,V>

Parameters:

key - the key

Returns:

the value of the mapping with the specified key

put

public V put(K key,
             V value)

Maps the specified key to the specified value.

Specified by:

put in interface Map<K,V>

Overrides:

put in class 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

putAll

public 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.

Specified by:

putAll in interface Map<K,V>

Overrides:

putAll in class AbstractMap<K,V>

Parameters:

map - the Map to copy mappings from

Throws:

NullPointerException - if the given map is null

remove

public V remove(Object key)

Removes a mapping with the specified key from this IdentityHashMap.

Specified by:

remove in interface Map<K,V>

Overrides:

remove in class AbstractMap<K,V>

Parameters:

key - the key of the mapping to remove

Returns:

the value of the removed mapping, or null if key is not a key in this Map

entrySet

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

Returns a Set of the mappings contained in this IdentityHashMap. Each element in the set is a Map.Entry. The set is backed by this Map so changes to one are reflected by the other. The set does not support adding.

Specified by:

entrySet in interface Map<K,V>

Specified by:

entrySet in class AbstractMap<K,V>

Returns:

a Set of the mappings

keySet

public Set<K> keySet()

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

Specified by:

keySet in interface Map<K,V>

Overrides:

keySet in class AbstractMap<K,V>

Returns:

a Set of the keys

values

public Collection<V> values()

Returns a Collection of the values contained in this IdentityHashMap. The collection is backed by this IdentityHashMap so changes to one are reflected by the other. The collection does not support adding.

Specified by:

values in interface Map<K,V>

Overrides:

values in class AbstractMap<K,V>

Returns:

a Collection of the values

equals

public boolean equals(Object object)

Compares this map with other objects. This map is equal to another map is it represents the same set of mappings. With this map, two mappings are the same if both the key and the value are equal by reference. When compared with a map that is not an IdentityHashMap, the equals method is not necessarily symmetric (a.equals(b) implies b.equals(a)) nor transitive (a.equals(b) and b.equals(c) implies a.equals(c)).

Specified by:

equals in interface Map<K,V>

Overrides:

equals in class AbstractMap<K,V>

Parameters:

object - the object to compare with this object

Returns:

whether the argument object is equal to this object

See Also:

AbstractMap.hashCode()

clone

public Object clone()

Returns a new IdentityHashMap with the same mappings and size as this one.

Overrides:

clone in class AbstractMap<K,V>

Returns:

a shallow copy of this IdentityHashMap

See Also:

Cloneable

isEmpty

public boolean isEmpty()

Returns if this IdentityHashMap has no elements, a size of zero.

Specified by:

isEmpty in interface Map<K,V>

Overrides:

isEmpty in class AbstractMap<K,V>

Returns:

true if this IdentityHashMap has no elements, false otherwise

See Also:

size

size

public int size()

Returns the number of mappings in this IdentityHashMap.

Specified by:

size in interface Map<K,V>

Overrides:

size in class AbstractMap<K,V>

Returns:

the number of mappings in this IdentityHashMap