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0N/A * particular file as subject to the "Classpath" exception as provided
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0N/A */
0N/A
0N/Apackage java.lang.ref;
0N/A
0N/A
0N/A/**
0N/A * Phantom reference objects, which are enqueued after the collector
0N/A * determines that their referents may otherwise be reclaimed. Phantom
0N/A * references are most often used for scheduling pre-mortem cleanup actions in
0N/A * a more flexible way than is possible with the Java finalization mechanism.
0N/A *
0N/A * <p> If the garbage collector determines at a certain point in time that the
0N/A * referent of a phantom reference is <a
0N/A * href="package-summary.html#reachability">phantom reachable</a>, then at that
0N/A * time or at some later time it will enqueue the reference.
0N/A *
0N/A * <p> In order to ensure that a reclaimable object remains so, the referent of
0N/A * a phantom reference may not be retrieved: The <code>get</code> method of a
0N/A * phantom reference always returns <code>null</code>.
0N/A *
0N/A * <p> Unlike soft and weak references, phantom references are not
0N/A * automatically cleared by the garbage collector as they are enqueued. An
0N/A * object that is reachable via phantom references will remain so until all
0N/A * such references are cleared or themselves become unreachable.
0N/A *
0N/A * @author Mark Reinhold
0N/A * @since 1.2
0N/A */
0N/A
0N/Apublic class PhantomReference<T> extends Reference<T> {
0N/A
0N/A /**
0N/A * Returns this reference object's referent. Because the referent of a
0N/A * phantom reference is always inaccessible, this method always returns
0N/A * <code>null</code>.
0N/A *
0N/A * @return <code>null</code>
0N/A */
0N/A public T get() {
0N/A return null;
0N/A }
0N/A
0N/A /**
0N/A * Creates a new phantom reference that refers to the given object and
0N/A * is registered with the given queue.
0N/A *
0N/A * <p> It is possible to create a phantom reference with a <tt>null</tt>
0N/A * queue, but such a reference is completely useless: Its <tt>get</tt>
0N/A * method will always return null and, since it does not have a queue, it
0N/A * will never be enqueued.
0N/A *
0N/A * @param referent the object the new phantom reference will refer to
0N/A * @param q the queue with which the reference is to be registered,
0N/A * or <tt>null</tt> if registration is not required
0N/A */
0N/A public PhantomReference(T referent, ReferenceQueue<? super T> q) {
0N/A super(referent, q);
0N/A }
0N/A
0N/A}