1 /*
 2  * Copyright (c) 1997, 2022, 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  *
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19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20  *
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22  * or visit www.oracle.com if you need additional information or have any
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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  * @param <T> the type of the referent
44  *
45  * @author   Mark Reinhold
46  * @since    1.2
47  */
48 
49 public non-sealed class WeakReference<@jdk.internal.RequiresIdentity T> extends Reference<T> {
50 
51     /**
52      * Creates a new weak reference that refers to the given object.  The new
53      * reference is not registered with any queue.
54      *
55      * @param referent object the new weak reference will refer to
56      */
57     public WeakReference(@jdk.internal.RequiresIdentity T referent) {
58         super(referent);
59     }
60 
61     /**
62      * Creates a new weak reference that refers to the given object and is
63      * registered with the given queue.
64      *
65      * @param referent object the new weak reference will refer to
66      * @param q the queue with which the reference is to be registered,
67      *          or {@code null} if registration is not required
68      */
69     public WeakReference(@jdk.internal.RequiresIdentity T referent, ReferenceQueue<? super T> q) {
70         super(referent, q);
71     }
72 
73 }