Added in API level 1

PhantomReference

public class PhantomReference
extends Reference<T>

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


Phantom reference objects, which are enqueued after the collector determines that their referents may otherwise be reclaimed. Phantom references are most often used to schedule post-mortem cleanup actions.

Suppose the garbage collector determines at a certain point in time that an object is phantom reachable. At that time it will atomically clear all phantom references to that object and all phantom references to any other phantom-reachable objects from which that object is reachable. At the same time or at some later time it will enqueue those newly-cleared phantom references that are registered with reference queues.

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.

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.

Inherited methods

Public constructors

PhantomReference

Added in API level 1
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 T: the object the new phantom reference will refer to

q ReferenceQueue: the queue with which the reference is to be registered, or null if registration is not required

Public methods

get

Added in API level 1
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
T null