PhantomReference (Java 2 Platform SE v1.4.1_"07")

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JavaTM 2 Platform
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## java.lang.ref
Class PhantomReference

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

public class PhantomReference
extends Reference

Phantom reference objects, which are enqueued after the collector determines that their referents may otherwise be reclaimed. Phantom references are most often used for scheduling pre-mortem cleanup actions in a more flexible way than is possible with the Java finalization mechanism.

If the garbage collector determines at a certain point in time that the referent of a phantom reference is phantom reachable, then at that time or at some later time it 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:
  1.2

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

Method Summary
`Object` | `get()` Returns this reference object's referent.

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)

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

Parameters:
  `referent` - the object the new phantom reference will refer to
  `q` - queue the phantom reference is registered with
Throws:
  `NullPointerException` - If the `queue` argument is `null`

Method Detail

### get

    public Object get()

  Returns this reference object's referent. Because the referent of a phantom reference is always inaccessible, this method always returns `null`.

  Overrides:
    `get` in class `Reference`
  Returns:
    `null`

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For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.

Copyright 2002 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms.