@Deprecated
public final class WeakHasherMap<K,V>
extends java.util.AbstractMap<K,V>
implements java.util.Map<K,V>
WeakHashMap from JDK 1.2.2,
that adds a constructor that takes a Hasher argument.
I also replaced uses of hashCode() and equals() by uses of Hasher,
where appropriate.
I've changed the name so that this version is not used accidentally.
It is slightly less efficient, in the absence of a Hasher, and has
not been as extensively tested.
Map implementation with weak keys.
An entry in a WeakHashMap 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 WeakHashMap may be constructed using the
Collections.synchronizedMap method.
This class is intended primarily for use with key objects whose
equals methods test for object identity using the
== operator. Once such a key is discarded it can never be
recreated, so it is impossible to do a lookup of that key in a
WeakHashMap at some later time and be surprised that its entry
has been removed. This class will work perfectly well with key objects
whose equals methods are not based upon object identity, such
as String instances. With such recreatable key objects,
however, the automatic removal of WeakHashMap entries whose
keys have been discarded may prove to be confusing.
The behavior of the WeakHashMap 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
WeakHashMap may behave as though an unknown thread is silently
removing entries. In particular, even if you synchronize on a
WeakHashMap 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 WeakHashMap 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
WeakHashMap 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 WeakHashMap 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. This problem
may be fixed in a future release.
HashMap,
WeakReference| Constructor and Description |
|---|
WeakHasherMap()
Deprecated.
Constructs a new, empty
WeakHashMap with the default
capacity and the default load factor, which is 0.75. |
WeakHasherMap(Hasher h)
Deprecated.
Constructs a new, empty
WeakHashMap with the default
capacity and the default load factor, which is 0.75. |
WeakHasherMap(int initialCapacity)
Deprecated.
Constructs a new, empty
WeakHashMap with the given
initial capacity and the default load factor, which is
0.75. |
WeakHasherMap(int initialCapacity,
float loadFactor)
Deprecated.
Constructs a new, empty
WeakHashMap with the given
initial capacity and the given load factor. |
| 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. |
java.util.Set<java.util.Map.Entry<K,V>> |
entrySet()
Deprecated.
Returns a
Set view of the mappings in this map. |
V |
get(java.lang.Object key)
Deprecated.
Returns the value to which this map maps the specified
key. |
boolean |
isEmpty()
Deprecated.
Returns
true if this map contains no key-value mappings. |
V |
put(K key,
V value)
Deprecated.
Updates this map so that the given
key maps to the given
value. |
V |
remove(java.lang.Object key)
Deprecated.
Removes the mapping for the given
key from this map, if
present. |
int |
size()
Deprecated.
Returns the number of key-value mappings in this map.
|
clone, containsValue, equals, hashCode, keySet, putAll, toString, valuespublic WeakHasherMap(int initialCapacity,
float loadFactor)
WeakHashMap with the given
initial capacity and the given load factor.initialCapacity - the initial capacity of the
WeakHashMaploadFactor - the load factor of the WeakHashMapjava.lang.IllegalArgumentException - If the initial capacity is less than
zero, or if the load factor is
nonpositivepublic WeakHasherMap(int initialCapacity)
WeakHashMap with the given
initial capacity and the default load factor, which is
0.75.initialCapacity - the initial capacity of the
WeakHashMapjava.lang.IllegalArgumentException - If the initial capacity is less than
zeropublic WeakHasherMap()
WeakHashMap with the default
capacity and the default load factor, which is 0.75.public WeakHasherMap(Hasher h)
WeakHashMap with the default
capacity and the default load factor, which is 0.75.
The WeakHashMap uses the specified hasher for hashing
keys and comparing them for equality.h - the Hasher to use when hashing values for this mappublic int size()
Map interface, the time required by this operation is
linear in the size of the map.public boolean isEmpty()
true if this map contains no key-value mappings.public boolean containsKey(java.lang.Object key)
true if this map contains a mapping for the
specified key.public V get(java.lang.Object key)
key.
If this map does not contain a value for this key, then return
null.public V put(K key, V value)
key maps to the given
value. If the map previously contained a mapping for
key then that mapping is replaced and the previous value is
returned.put in interface java.util.Map<K,V>put in class java.util.AbstractMap<K,V>key - the key that is to be mapped to the given
valuevalue - the value to which the given key is to be
mappednull if if there was no mapping for the keypublic V remove(java.lang.Object key)
key from this map, if
present.public void clear()