@Deprecated
public class WeakIdentityHashMap<K,V>
extends java.util.AbstractMap<K,V>
implements java.util.Map<K,V>
WeakHashMap and
IdentityHashMap.
The implementation is a modified version of WeakHashMap
from JDK 1.5, which differs from the original in two ways:
IdentityHashMap
for more information on the changes made in an identity hash map..
Map implementation with weak
keys. 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,
so this class behaves somewhat differently than 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 WeakIdentityHashMap may be constructed using the
Collections.synchronizedMap method.
The behavior of the WeakIdentityHashMap 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 WeakIdentityHashMap may behave as though an
unknown thread is silently removing entries. In particular, even
if you synchronize on a WeakIdentityHashMap 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 set, and
the entry set to yield successively smaller numbers of elements.
Each key object in a WeakIdentityHashMap 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
WeakIdentityHashMap 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
WeakIdentityHashMap 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. 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 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 or add methods, the iterator will throw a
ConcurrentModificationException. 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.
HashMap,
WeakReference| Constructor and Description |
|---|
WeakIdentityHashMap()
Deprecated.
Constructs a new, empty
WeakIdentityHashMap with the
default initial capacity (16) and the default load factor
(0.75). |
WeakIdentityHashMap(int initialCapacity)
Deprecated.
Constructs a new, empty
WeakIdentityHashMap with the
given initial capacity and the default load factor, which is
0.75. |
WeakIdentityHashMap(int initialCapacity,
float loadFactor)
Deprecated.
Constructs a new, empty
WeakIdentityHashMap with the
given initial capacity and the given load factor. |
WeakIdentityHashMap(java.util.Map<? extends K,? extends V> t)
Deprecated.
Constructs a new
WeakIdentityHashMap with the same
mappings as the specified Map. |
| Modifier and Type | Method and Description |
|---|---|
void |
clear()
Deprecated.
Removes all mappings from this map.
|
boolean |
containsKey(java.lang.Object key)
Deprecated.
Returns
true if this map contains a mapping for the
specified key. |
boolean |
containsValue(java.lang.Object value)
Deprecated.
Returns
true if this map maps one or more keys to the
specified value. |
java.util.Set<java.util.Map.Entry<K,V>> |
entrySet()
Deprecated.
Returns a collection view of the mappings contained in this map.
|
V |
get(java.lang.Object key)
Deprecated.
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()
Deprecated.
Returns
true if this map contains no key-value mappings. |
java.util.Set<K> |
keySet()
Deprecated.
Returns a set view of the keys contained in this map.
|
V |
put(K key,
V value)
Deprecated.
Associates the specified value with the specified key in this map.
|
void |
putAll(java.util.Map<? extends K,? extends V> m)
Deprecated.
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(java.lang.Object key)
Deprecated.
Removes the mapping for this key from this map if present.
|
int |
size()
Deprecated.
Returns the number of key-value mappings in this map.
|
java.util.Collection<V> |
values()
Deprecated.
Returns a collection view of the values contained in this map.
|
public WeakIdentityHashMap(int initialCapacity,
float loadFactor)
WeakIdentityHashMap with the
given initial capacity and the given load factor.initialCapacity - the initial capacity of the
WeakIdentityHashMaploadFactor - the load factor of the
WeakIdentityHashMapjava.lang.IllegalArgumentException - If the initial capacity is negative,
or if the load factor is nonpositivepublic WeakIdentityHashMap(int initialCapacity)
WeakIdentityHashMap with the
given initial capacity and the default load factor, which is
0.75.initialCapacity - the initial capacity of the
WeakIdentityHashMapjava.lang.IllegalArgumentException - If the initial capacity is negativepublic WeakIdentityHashMap()
WeakIdentityHashMap with the
default initial capacity (16) and the default load factor
(0.75).public WeakIdentityHashMap(java.util.Map<? extends K,? extends V> t)
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.t - the map whose mappings are to be placed in this mapjava.lang.NullPointerException - if the specified map is nullpublic int size()
public boolean isEmpty()
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.public V get(java.lang.Object key)
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.get in interface java.util.Map<K,V>get in class java.util.AbstractMap<K,V>key - the key whose associated value is to be returnednull if the map contains no mapping for this key.put(Object, Object)public boolean containsKey(java.lang.Object key)
true if this map contains a mapping for the
specified key.public V put(K key, V value)
put in interface java.util.Map<K,V>put in class java.util.AbstractMap<K,V>key - key with which the specified value is to be associatedvalue - value to be associated with the specified keynull
if there was no mapping for key. A null return can
also indicate that the HashMap previously associated
null with the specified key.public void putAll(java.util.Map<? extends K,? extends V> m)
public V remove(java.lang.Object key)
remove in interface java.util.Map<K,V>remove in class java.util.AbstractMap<K,V>key - key whose mapping is to be removed from the mapnull
if there was no mapping for key. A null return can
also indicate that the map previously associated null
with the specified key.public void clear()
public boolean containsValue(java.lang.Object value)
true if this map maps one or more keys to the
specified value.public java.util.Set<K> keySet()
Iterator.remove,
Set.remove, removeAll, retainAll, and
clear operations. It does not support the add or
addAll operations.public java.util.Collection<V> values()
Iterator.remove, Collection.remove,
removeAll, retainAll, and clear operations.
It does not support the add or addAll operations.public java.util.Set<java.util.Map.Entry<K,V>> entrySet()
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.