IdentityHashMap<K,V> (GNU Classpath 0.94-pre Documentation)

This class provides a hashtable-backed implementation of the Map interface, but uses object identity to do its hashing. In fact, it uses object identity for comparing values, as well. It uses a linear-probe hash table, which may have faster performance than the chaining employed by HashMap.

WARNING: This is not a general purpose map. Because it uses System.identityHashCode and ==, instead of hashCode and equals, for comparison, it violated Map's general contract, and may cause undefined behavior when compared to other maps which are not IdentityHashMaps. This is designed only for the rare cases when identity semantics are needed. An example use is topology-preserving graph transformations, such as deep cloning, or as proxy object mapping such as in debugging.

This map permits null keys and values, and does not guarantee that elements will stay in the same order over time. The basic operations (get and put) take constant time, provided System.identityHashCode is decent. You can tune the behavior by specifying the expected maximum size. As more elements are added, the map may need to allocate a larger table, which can be expensive.

This implementation is unsynchronized. If you want multi-thread access to be consistent, you must synchronize it, perhaps by using Collections.synchronizedMap(new IdentityHashMap(...));. The iterators are fail-fast, meaning that a structural modification made to the map outside of an iterator's remove method cause the iterator, and in the case of the entrySet, the Map.Entry, to fail with a {@link ConcurrentModificationException}.

Since: 1.4

UNKNOWN: updated to 1.4

Constructor Summary
	IdentityHashMap() Create a new IdentityHashMap with the default capacity (21 entries).
	IdentityHashMap(int max) Create a new IdentityHashMap with the indicated number of entries.
	IdentityHashMap(Map<? extends K,? extends V> m) Create a new IdentityHashMap whose contents are taken from the given Map.

Method Summary
void	clear() Remove all mappings from this map.
Object	clone() Creates a shallow copy where keys and values are not cloned.
boolean	containsKey(Object key) Tests whether the specified key is in this map.
boolean	containsValue(Object value) Returns true if this HashMap contains the value.
Set<Entry<K,V>>	entrySet() Returns a "set view" of this Map's entries.
boolean	equals(Object o) Compares two maps for equality.
V	get(Object key) Return the value in this Map associated with the supplied key, or `null` if the key maps to nothing.
int	hashCode() Returns the hashcode of this map.
boolean	isEmpty() Returns true if there are no key-value mappings currently in this Map
Set<K>	keySet() Returns a "set view" of this Map's keys.
V	put(K key, V value) Puts the supplied value into the Map, mapped by the supplied key.
void	putAll(Map<? extends K,? extends V> m) Copies all of the mappings from the specified map to this.
V	remove(Object key) Removes from the HashMap and returns the value which is mapped by the supplied key.
int	size() Returns the number of kay-value mappings currently in this Map
Collection<V>	values() Returns a "collection view" (or "bag view") of this Map's values.

Tests whether the specified key is in this map. Unlike normal Maps, this test uses entry == key instead of entry == null ? key == null : entry.equals(key).

Parameters: key the key to look for

Returns: true if the key is contained in the map

Class IdentityHashMap<K,V>