PhantomReference

extends Reference<T>

java.lang.Object
↳	java.lang.ref.Reference<T>
	↳	java.lang.ref.PhantomReference<T>

Known Direct Subclasses

Cleaner

Class Overview

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.

Summary

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

Public Methods
T	get() Returns this reference object's referent.

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Inherited Methods

From class java.lang.ref.Reference

From class java.lang.Object

Object	clone() Creates and returns a copy of this object.
boolean	equals(Object obj) Indicates whether some other object is "equal to" this one.
void	finalize() Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
final Class<?>	getClass() Returns the runtime class of this `Object`.
int	hashCode() Returns a hash code value for the object.
final void	notify() Wakes up a single thread that is waiting on this object's monitor.
final void	notifyAll() Wakes up all threads that are waiting on this object's monitor.
String	toString() Returns a string representation of the object.
final void	wait() Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object.
final void	wait(long timeout, int nanos) Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object, or some other thread interrupts the current thread, or a certain amount of real time has elapsed.
final void	wait(long timeout) Causes the current thread to wait until either another thread invokes the `notify()` method or the `notifyAll()` method for this object, or a specified amount of time has elapsed.

Public Constructors

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

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

It is possible to create a phantom reference with a null queue, but such a reference is completely useless: Its get method will always return null and, since it does not have a queue, it will never be enqueued.

Parameters

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

Public Methods

public T get ()

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

Returns

null

Classes