META-INF.modules.java.base.classes.java.lang.ref.PhantomReference Maven / Gradle / Ivy
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package java.lang.ref;
/**
* 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 {@code get} method of a
* phantom reference always returns {@code null}.
*
* @author Mark Reinhold
* @since 1.2
*/
public class PhantomReference extends Reference {
/**
* Returns this reference object's referent. Because the referent of a
* phantom reference is always inaccessible, this method always returns
* {@code null}.
*
* @return {@code null}
*/
public T get() {
return null;
}
/**
* 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 {@code null}
* queue, but such a reference is completely useless: Its {@code get}
* method will always return {@code null} and, since it does not have a queue,
* it will never be enqueued.
*
* @param referent the object the new phantom reference will refer to
* @param q the queue with which the reference is to be registered,
* or {@code null} if registration is not required
*/
public PhantomReference(T referent, ReferenceQueue q) {
super(referent, q);
}
}