1 /*
   2  * Copyright (c) 1997, 2003, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package java.lang.ref;
  27 
  28 
  29 /**
  30  * Weak reference objects, which do not prevent their referents from being
  31  * made finalizable, finalized, and then reclaimed.  Weak references are most
  32  * often used to implement canonicalizing mappings.
  33  *
  34  * <p> Suppose that the garbage collector determines at a certain point in time
  35  * that an object is <a href="package-summary.html#reachability">weakly
  36  * reachable</a>.  At that time it will atomically clear all weak references to
  37  * that object and all weak references to any other weakly-reachable objects
  38  * from which that object is reachable through a chain of strong and soft
  39  * references.  At the same time it will declare all of the formerly
  40  * weakly-reachable objects to be finalizable.  At the same time or at some
  41  * later time it will enqueue those newly-cleared weak references that are
  42  * registered with reference queues.
  43  *
  44  * @author   Mark Reinhold
  45  * @since    1.2
  46  */
  47 
  48 public class WeakReference<T> extends Reference<T> {
  49 
  50     /**
  51      * Creates a new weak reference that refers to the given object.  The new
  52      * reference is not registered with any queue.
  53      *
  54      * @param referent object the new weak reference will refer to
  55      */
  56     public WeakReference(T referent) {
  57         super(referent);
  58     }
  59 
  60     /**
  61      * Creates a new weak reference that refers to the given object and is
  62      * registered with the given queue.
  63      *
  64      * @param referent object the new weak reference will refer to
  65      * @param q the queue with which the reference is to be registered,
  66      *          or {@code null} if registration is not required
  67      */
  68     public WeakReference(T referent, ReferenceQueue<? super T> q) {
  69         super(referent, q);
  70     }
  71 
  72 }