java.lang.ref

Class WeakReference<T>

java.lang.Object

java.lang.ref.Reference<T>

java.lang.ref.WeakReference<T>

public class WeakReference<T>
extends Reference<T>

Implements a weak reference, which is the middle of the three types of references. Once the garbage collector decides that an object obj is is weakly-reachable, the following happens:

• A set ref of references is determined. ref contains the following elements:
  • All weak references pointing to obj.
  • All weak references pointing to objects from which obj is either strongly or softly reachable.
• All references in ref are atomically cleared.
• All objects formerly being referenced by ref become eligible for finalization.
• At some future point, all references in ref will be enqueued with their corresponding reference queues, if any.

Weak references are useful for mappings that should have their entries removed automatically once they are not referenced any more (from outside). The difference between a SoftReference and a WeakReference is the point of time at which the decision is made to clear and enqueue the reference:

• A SoftReference should be cleared and enqueued as late as possible, that is, in case the VM is in danger of running out of memory.
• A WeakReference may be cleared and enqueued as soon as is known to be weakly-referenced.

Field Summary

Fields inherited from class java.lang.ref.Reference

pendingNext

Constructor Summary

Constructors

Constructor and Description
WeakReference(T r) Constructs a new weak reference to the given referent.
WeakReference(T r, ReferenceQueue<? super T> q) Constructs a new weak reference to the given referent.

Method Summary

Methods inherited from class java.lang.ref.Reference

clear, enqueue, enqueueInternal, get, isEnqueued

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

WeakReference

public WeakReference(T r)

Constructs a new weak reference to the given referent. The newly created reference is not registered with any reference queue.

Parameters:

r - the referent to track

WeakReference

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

Constructs a new weak reference to the given referent. The newly created reference is registered with the given reference queue.

Parameters:

r - the referent to track

q - the queue to register to the reference object with. A null value results in a weak reference that is not associated with any queue.