WeakReference

Page Summary

• WeakReference objects do not prevent their referents from being garbage collected.

• When the garbage collector identifies an object as weakly reachable, it clears all weak references to that object and makes it eligible for finalization.

• WeakReference can be used to implement canonicalizing mappings, and they can optionally be registered with a ReferenceQueue for processing when the referent becomes weakly reachable.

• You can create a WeakReference with or without associating it with a ReferenceQueue.

public class WeakReference extends Reference<T>

Weak reference objects, which do not prevent their referents from being made finalizable, finalized, and then reclaimed. Weak references are most often used to implement canonicalizing mappings.

Suppose that the garbage collector determines at a certain point in time that an object is weakly reachable. At that time it will atomically clear all weak references to that object and all weak references to any other weakly-reachable objects from which that object is reachable through a chain of strong and soft references. At the same time it will declare all of the formerly weakly-reachable objects to be finalizable. At the same time or at some later time it will enqueue those newly-cleared weak references that are registered with reference queues.

Public Constructor Summary

	WeakReference(T referent) Creates a new weak reference that refers to the given object.
	WeakReference(T referent, ReferenceQueue<? super T> q) Creates a new weak reference that refers to the given object and is registered with the given queue.

Inherited Method Summary

From class java.lang.ref.Reference

void	clear() Clears this reference object.
boolean	enqueue() Adds this reference object to the queue with which it is registered, if any.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
T	get() Returns this reference object's referent.
boolean	isEnqueued() Tells whether or not this reference object has been enqueued, either by the program or by the garbage collector.

From class java.lang.Object

Object	clone() Creates and returns a copy of this Object.
boolean	equals(Object obj) Compares this instance with the specified object and indicates if they are equal.
void	finalize() Invoked when the garbage collector has detected that this instance is no longer reachable.
final Class<?>	getClass() Returns the unique instance of Class that represents this object's class.
int	hashCode() Returns an integer hash code for this object.
final void	notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
final void	notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up.
String	toString() Returns a string containing a concise, human-readable description of this object.
final void	wait(long timeout, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait(long timeout) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
final void	wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object.

Public Constructors

public WeakReference (T referent)

Creates a new weak reference that refers to the given object. The new reference is not registered with any queue.

Parameters

referent	object the new weak reference will refer to

public WeakReference (T referent, ReferenceQueue<? super T> q)

Creates a new weak reference that refers to the given object and is registered with the given queue.

Parameters

referent	object the new weak reference will refer to
q	the queue with which the reference is to be registered, or null if registration is not required