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

From class


        
          java.lang.ref.Reference

`void`	`clear()` Clears this reference object.
`Object`	`clone()` Throws `CloneNotSupportedException`.
`boolean`	`enqueue()` Adds this reference object to the queue with which it is registered, if any.
`T`	`get()` Returns this reference object's referent.
`boolean`	`isEnqueued()` This method was deprecated in API level 31. This method was never implemented to test if a reference object has been cleared and enqueued as it was previously specified since 1.2. This method could be misused due to the inherent race condition or without an associated `ReferenceQueue`. An application relying on this method to release critical resources could cause serious performance issue. An application should use `ReferenceQueue` to reliably determine what reference objects that have been enqueued or `refersTo(null)` to determine if this reference object has been cleared.
`static void`	`reachabilityFence(Object ref)` Ensures that the object referenced by the given reference remains strongly reachable, regardless of any prior actions of the program that might otherwise cause the object to become unreachable; thus, the referenced object is not reclaimable by garbage collection at least until after the invocation of this method.
`final boolean`	`refersTo(T obj)` Tests if the referent of this reference object is `obj`.

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(long timeoutMillis, int nanos)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis)` Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait()` Causes the current thread to wait until it is awakened, typically by being notified or interrupted.

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`