Added in API level 1

PhantomReference

open class PhantomReference<T : Any!> : Reference<T>

kotlin.Any
↳	java.lang.ref.Reference<T>
	↳	java.lang.ref.PhantomReference

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
`<init>(referent: T, q: ReferenceQueue<in T>!)` Creates a new phantom reference that refers to the given object and is registered with the given queue.

Public methods
open T?	`get()` Returns this reference object's referent.

Inherited functions

From class Reference

`Unit`	`clear()` Clears this reference object. Invoking this method will not cause this object to be enqueued. This method is invoked only by Java code; when the garbage collector clears references it does so directly, without invoking this method.
`Boolean`	`enqueue()` Adds this reference object to the queue with which it is registered, if any. This method is invoked only by Java code; when the garbage collector enqueues references it does so directly, without invoking this method.
`Boolean`	`isEnqueued()` Tells whether or not this reference object has been enqueued, either by the program or by the garbage collector. If this reference object was not registered with a queue when it was created, then this method will always return `false`.
`Unit`	`reachabilityFence(ref: Any!)` 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. Invocation of this method does not itself initiate garbage collection or finalization. This method establishes an ordering for strong reachability with respect to garbage collection. It controls relations that are otherwise only implicit in a program -- the reachability conditions triggering garbage collection. This method is designed for use in uncommon situations of premature finalization where using `synchronized` blocks or methods, or using other synchronization facilities are not possible or do not provide the desired control. This method is applicable only when reclamation may have visible effects, which is possible for objects with finalizers (See Section 12.6 17 of The Java™ Language Specification) that are implemented in ways that rely on ordering control for correctness.

Public constructors

<init>

Added in API level 1

PhantomReference(
    referent: T, 
    q: ReferenceQueue<in T>!)

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<in T>!: 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

open fun get(): T?

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

Return
`T?`	`null`