1 /*
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 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
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 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.
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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  * <p>
34  * The referent must not be an instance of a {@linkplain Class#isValue()
35  * value class}; such a value can never have another reference to it
36  * and cannot be held in a reference type.
37  *
38  * <p> Suppose that the garbage collector determines at a certain point in time
39  * that an object is <a href="package-summary.html#reachability">weakly
40  * reachable</a>.  At that time it will atomically clear all weak references to
41  * that object and all weak references to any other weakly-reachable objects
42  * from which that object is reachable through a chain of strong and soft
43  * references.  At the same time it will declare all of the formerly
44  * weakly-reachable objects to be finalizable.  At the same time or at some
45  * later time it will enqueue those newly-cleared weak references that are
46  * registered with reference queues.
47  *
48  * @author   Mark Reinhold
49  * @since    1.2
50  */
51 
52 public non-sealed class WeakReference<T> extends Reference<T> {
53 
54     /**
55      * Creates a new weak reference that refers to the given object.  The new
56      * reference is not registered with any queue.
57      *
58      * @param referent object the new weak reference will refer to
59      * @throws IllegalArgumentException if the referent is an instance of a
60      *         {@link Class#isValue() value class}
61      */
62     public WeakReference(T referent) {
63         super(referent);
64     }
65 
66     /**
67      * Creates a new weak reference that refers to the given object and is
68      * registered with the given queue.
69      *
70      * @param referent object the new weak reference will refer to
71      * @param q the queue with which the reference is to be registered,
72      *          or {@code null} if registration is not required
73      * @throws IllegalArgumentException if the referent is an instance of a
74      *         {@link Class#isValue() value class}
75      */
76     public WeakReference(T referent, ReferenceQueue<? super T> q) {
77         super(referent, q);
78     }
79 
80 }