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 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.
*
* @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
* null.
*
* @return 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 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.
*
* @param referent the object the new phantom reference will refer to
* @param q the queue with which the reference is to be registered,
* or null if registration is not required
*/
public PhantomReference(T referent, ReferenceQueue q) {
super(referent, q);
}
}