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Java Platform 1.2
Beta 4

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Class java.lang.ref.PhantomReference

java.lang.Object
  |
  +--java.lang.ref.Reference
        |
        +--java.lang.ref.PhantomReference

public class PhantomReference

extends Reference

Phantom reference objects, for use in scheduling pre-mortem cleanup actions.

A phantom reference is a reference object that remains valid even after the collector determines that its referent may otherwise be reclaimed. If the garbage collector determines at a certain point in time that the referent of a phantom reference is no longer strongly reachable, has no soft or weak references, and has been finalized, then at some later time the collector will enqueue the reference.

In order to ensure that a reclaimable object remains so, the referent of a phantom reference may not be retrieved: The get method of a phantom reference always returns null.

Unlike soft and weak references, phantom references are not automatically cleared by the garbage collector as they are enqueued. An object that is reachable via phantom references will remain so until all such references are cleared or themselves become unreachable.

Since:

JDK1.2

See Also:

Reference

Constructor Summary

PhantomReference(Object referent, ReferenceQueue q)
Create a new phantom reference that refers to the given object and is registered with the given queue.

Method Summary

Object

get() Return null, since the referent of a phantom reference is always inaccessible.

Methods inherited from class java.lang.ref.Reference

clear , enqueue , isEnqueued

Methods inherited from class java.lang.Object

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

Constructor Detail

PhantomReference

public PhantomReference(Object referent,
                        ReferenceQueue q)

Create a new phantom reference that refers to the given object and is registered with the given queue.

Throws:

NullPointerException - If the queue argument is null

Method Detail

get

public Object get()

Return null, since the referent of a phantom reference is always inaccessible.

Overrides:

get in class Reference