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com.sun.jmx.mbeanserver

pack-priv Class WeakIdentityHashMap<K, V>

extends Object
Class Inheritance
Static Imports
com.sun.jmx.mbeanserver.Util.*

A map where keys are compared using identity comparison (like IdentityHashMap) but where the presence of an object as a key in the map does not prevent it being garbage collected (like WeakHashMap). This class does not implement the Map interface because it is difficult to ensure correct semantics for iterators over the entrySet().

Because we do not implement Map, we do not copy the questionable interface where you can call get(k) or remove(k) for any type of k, which of course can only have an effect if k is of type K.

This map does not support null keys.

Nested and Inner Type Summary

Modifier and TypeClass and Description
private static class
WeakIdentityHashMap.IdentityWeakReference<T>

WeakReference where equals and hashCode are based on the referent.

Field Summary

Modifier and TypeField and Description
private Map<WeakReference<K>, V>
map

private ReferenceQueue<K>
refQueue

Constructor Summary

AccessConstructor and Description
private
WeakIdentityHashMap()

Method Summary

Modifier and TypeMethod and Description
private void
expunge()

pack-priv V
get(K key)

pack-priv static <K, V> WeakIdentityHashMap<K, V>
make()

private WeakReference<K>
makeReference(K referent)

private WeakReference<K>
makeReference(K referent, ReferenceQueue<K> q)

public V
put(K key, V value)

public V
remove(K key)

Inherited from java.lang.Object:
cloneequalsfinalizegetClasshashCodenotifynotifyAlltoStringwaitwaitwait

Field Detail

mapback to summary
private Map<WeakReference<K>, V> map
refQueueback to summary
private ReferenceQueue<K> refQueue

Constructor Detail

WeakIdentityHashMapback to summary
private WeakIdentityHashMap()

Method Detail

expungeback to summary
private void expunge()
getback to summary
pack-priv V get(K key)
makeback to summary
pack-priv static <K, V> WeakIdentityHashMap<K, V> make()
makeReferenceback to summary
private WeakReference<K> makeReference(K referent)
makeReferenceback to summary
private WeakReference<K> makeReference(K referent, ReferenceQueue<K> q)
putback to summary
public V put(K key, V value)
removeback to summary
public V remove(K key)
com.sun.jmx.mbeanserver back to summary

private Class WeakIdentityHashMap.IdentityWeakReference<T>

extends WeakReference<T>
Class Inheritance
WeakReference where equals and hashCode are based on the referent. More precisely, two objects are equal if they are identical or if they both have the same non-null referent. The hashCode is the value the original referent had. Even if the referent is cleared, the hashCode remains. Thus, objects of this class can be used as keys in hash-based maps and sets.

Field Summary

Modifier and TypeField and Description
private final int
hashCode

Constructor Summary

AccessConstructor and Description
pack-priv
IdentityWeakReference(T o)

pack-priv
IdentityWeakReference(T o, ReferenceQueue<T> q)

Method Summary

Modifier and TypeMethod and Description
public boolean
equals(Object o)

Overrides java.lang.Object.equals.

Indicates whether some other object is "equal to" this one.

public int
hashCode()

Overrides java.lang.Object.hashCode.

Returns a hash code value for this object.

Field Detail

hashCodeback to summary
private final int hashCode

Constructor Detail

IdentityWeakReferenceback to summary
pack-priv IdentityWeakReference(T o)
IdentityWeakReferenceback to summary
pack-priv IdentityWeakReference(T o, ReferenceQueue<T> q)

Method Detail

equalsback to summary
public boolean equals(Object o)

Overrides java.lang.Object.equals.

Doc from java.lang.Object.equals.

Indicates whether some other object is "equal to" this one.

The equals method implements an equivalence relation on non-null object references:

  • It is reflexive: for any non-null reference value x, x.equals(x) should return true.
  • It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
  • It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
  • It is consistent: for any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified.
  • For any non-null reference value x, x.equals(null) should return false.

An equivalence relation partitions the elements it operates on into equivalence classes; all the members of an equivalence class are equal to each other. Members of an equivalence class are substitutable for each other, at least for some purposes.

hashCodeback to summary
public int hashCode()

Overrides java.lang.Object.hashCode.

Doc from java.lang.Object.hashCode.

Returns a hash code value for this object. This method is supported for the benefit of hash tables such as those provided by java.util.HashMap.

The general contract of hashCode is:

  • Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
  • If two objects are equal according to the equals method, then calling the hashCode method on each of the two objects must produce the same integer result.
  • It is not required that if two objects are unequal according to the equals method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.