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 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(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.
`Any!`	`clone()` Throws `CloneNotSupportedException`. A `Reference` cannot be meaningfully cloned. Construct a new `Reference` instead.
`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()` Tests if this reference object is in its associated queue, if any. This method returns `true` only if all of the following conditions are met: this reference object was registered with a queue when it was created; and the garbage collector has added this reference object to the queue or `enqueue()` is called; and this reference object is not yet removed from the queue. Otherwise, this method returns `false`. This method may return `false` if this reference object has been cleared but not enqueued due to the race condition.
`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.
`Boolean`	`refersTo(obj: T)` Tests if the referent of this reference object is `obj`. Using a `null` `obj` returns `true` if the reference object has been cleared. Prefer this to a comparison with the result of `get`.

Public constructors