1 /*
   2  * Copyright (c) 1997, 2019, 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  * <p>
  34  * The referent must not be an instance of an inline class; such a value
  35  * can never have another reference to it and cannot be held in a reference type.
  36  *
  37  * <p> Suppose that the garbage collector determines at a certain point in time
  38  * that an object is <a href="package-summary.html#reachability">weakly
  39  * reachable</a>.  At that time it will atomically clear all weak references to
  40  * that object and all weak references to any other weakly-reachable objects
  41  * from which that object is reachable through a chain of strong and soft
  42  * references.  At the same time it will declare all of the formerly
  43  * weakly-reachable objects to be finalizable.  At the same time or at some
  44  * later time it will enqueue those newly-cleared weak references that are
  45  * registered with reference queues.
  46  *
  47  * @author   Mark Reinhold
  48  * @since    1.2
  49  */
  50 
  51 public class WeakReference<T> extends Reference<T> {
  52 
  53     /**
  54      * Creates a new weak reference that refers to the given object.  The new
  55      * reference is not registered with any queue.
  56      *
  57      * @param referent object the new weak reference will refer to
  58      * @throws IllegalArgumentException if the referent is an instance of an
  59      *         {@link Class#isInlineClass() inlineClass}
  60      */
  61     public WeakReference(T referent) {
  62         super(referent);
  63     }
  64 
  65     /**
  66      * Creates a new weak reference that refers to the given object and is
  67      * registered with the given queue.
  68      *
  69      * @param referent object the new weak reference will refer to
  70      * @param q the queue with which the reference is to be registered,
  71      *          or {@code null} if registration is not required
  72      * @throws IllegalArgumentException if the referent is an instance of an
  73      *         {@link Class#isInlineClass() inlineClass}
  74      */
  75     public WeakReference(T referent, ReferenceQueue<? super T> q) {
  76         super(referent, q);
  77     }
  78 
  79 }