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Summary: Ctors | Methods | Inherited Methods

# 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 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.

### Inherited methods
From class `java.lang.ref.Reference`
`void` | `clear()` Clears this reference object.
`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 is deprecated. 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.
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 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.
`final void` | `wait()` Causes the current thread to wait until another thread invokes the `notify()` method or the `notifyAll()` method for this object.

## Public constructors

### PhantomReference

    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

    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`

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