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 <tt>null</tt> if registration is not required
   67        */
   68       public WeakReference(T referent, ReferenceQueue<? super T> q) {
   69           super(referent, q);
   70       }
   71   
   72   }