--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/jdk/src/share/classes/java/lang/ref/PhantomReference.java	Sat Dec 01 00:00:00 2007 +0000
@@ -0,0 +1,83 @@
+/*
+ * Copyright 1997-2003 Sun Microsystems, Inc.  All Rights Reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Sun designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Sun in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
+ * CA 95054 USA or visit www.sun.com if you need additional information or
+ * have any questions.
+ */
+
+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.
+ *
+ * <p> If the garbage collector determines at a certain point in time that the
+ * referent of a phantom reference is <a
+ * href="package-summary.html#reachability">phantom reachable</a>, then at that
+ * time or at some later time it will enqueue the reference.
+ *
+ * <p> In order to ensure that a reclaimable object remains so, the referent of
+ * a phantom reference may not be retrieved: The <code>get</code> method of a
+ * phantom reference always returns <code>null</code>.
+ *
+ * <p> 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<T> extends Reference<T> {
+
+    /**
+     * Returns this reference object's referent.  Because the referent of a
+     * phantom reference is always inaccessible, this method always returns
+     * <code>null</code>.
+     *
+     * @return  <code>null</code>
+     */
+    public T get() {
+        return null;
+    }
+
+    /**
+     * Creates a new phantom reference that refers to the given object and
+     * is registered with the given queue.
+     *
+     * <p> It is possible to create a phantom reference with a <tt>null</tt>
+     * queue, but such a reference is completely useless: Its <tt>get</tt>
+     * 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 <tt>null</tt> if registration is not required
+     */
+    public PhantomReference(T referent, ReferenceQueue<? super T> q) {
+        super(referent, q);
+    }
+
+}