Module java.base
Package java.lang.ref

# Class PhantomReference

≠
public class PhantomReference<T>
extends java.lang.ref.Reference<T>
Comparing jdk-master and valhalla-csr-open

Type Parameters:
  `T` - the type of the referent

public non-sealed class PhantomReference<T> extends Reference<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.
Moved out of a paragraph.Moved to a division with class preview-block.
The referent must have object identityPREVIEW . When preview features are enabled, attempts to create a reference to a value objectPREVIEW result in an `IdentityException` PREVIEW .

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` . The `refersTo` method can be used to test whether some object is the referent of a phantom reference.

Since:
  1.2

## Constructors

- ≠
  public PhantomReference(T arg0, java.lang.ref.ReferenceQueue<? super T> arg1)
  Comparing jdk-master and valhalla-csr-open

  ### 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. Such a reference will never be enqueued.

  Parameters:
    `referent` - the object the new phantom reference will refer to
    `q` - the queue with which the reference is to be registered, or `null` if registration is not required
  Throws:
    `IdentityExceptionPREVIEW` - if the referent is not an `identity object` PREVIEW

## Methods

- =
  public T get()

## Summary

Differences
| Elements | Comments | Descriptions | Total
Added | Changed | Removed | Added | Changed | Removed | Added | Changed | Removed
--- | --- | --- | --- | --- | --- | --- | --- | ---
PhantomReference |  |  |  |  |  |  |  | 1 |  | 1
<init>(T,ReferenceQueue) |  |  |  |  |  |  | 4 |  |  | 4
Total |  |  |  |  |  |  | 4 | 1 |  | 5