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 * Phantom reference objects, which are enqueued after the collector
31 * determines that their referents may otherwise be reclaimed. Phantom
32 * references are most often used to schedule post-mortem cleanup actions.
33 *
34 * <p> Suppose the garbage collector determines at a certain point in time
35 * that an object is <a href="package-summary.html#reachability">
36 * phantom reachable</a>. At that time it will atomically clear
37 * all phantom references to that object and all phantom references to
38 * any other phantom-reachable objects from which that object is reachable.
39 * At the same time or at some later time it will enqueue those newly-cleared
40 * phantom references that are registered with reference queues.
41 *
42 * <p> In order to ensure that a reclaimable object remains so, the referent of
43 * a phantom reference may not be retrieved: The {@code get} method of a
44 * phantom reference always returns {@code null}.
45 *
46 * @author Mark Reinhold
47 * @since 1.2
48 */
49
50 public class PhantomReference<T> extends Reference<T> {
51
52 /**
55 * {@code null}.
56 *
57 * @return {@code null}
58 */
59 public T get() {
60 return null;
61 }
62
63 /**
64 * Creates a new phantom reference that refers to the given object and
65 * is registered with the given queue.
66 *
67 * <p> It is possible to create a phantom reference with a {@code null}
68 * queue, but such a reference is completely useless: Its {@code get}
69 * method will always return {@code null} and, since it does not have a queue,
70 * it will never be enqueued.
71 *
72 * @param referent the object the new phantom reference will refer to
73 * @param q the queue with which the reference is to be registered,
74 * or {@code null} if registration is not required
75 */
76 public PhantomReference(T referent, ReferenceQueue<? super T> q) {
77 super(referent, q);
78 }
79
80 }
|
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 * Phantom reference objects, which are enqueued after the collector
31 * determines that their referents may otherwise be reclaimed. Phantom
32 * references are most often used to schedule post-mortem cleanup actions.
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 the garbage collector determines at a certain point in time
38 * that an object is <a href="package-summary.html#reachability">
39 * phantom reachable</a>. At that time it will atomically clear
40 * all phantom references to that object and all phantom references to
41 * any other phantom-reachable objects from which that object is reachable.
42 * At the same time or at some later time it will enqueue those newly-cleared
43 * phantom references that are registered with reference queues.
44 *
45 * <p> In order to ensure that a reclaimable object remains so, the referent of
46 * a phantom reference may not be retrieved: The {@code get} method of a
47 * phantom reference always returns {@code null}.
48 *
49 * @author Mark Reinhold
50 * @since 1.2
51 */
52
53 public class PhantomReference<T> extends Reference<T> {
54
55 /**
58 * {@code null}.
59 *
60 * @return {@code null}
61 */
62 public T get() {
63 return null;
64 }
65
66 /**
67 * Creates a new phantom reference that refers to the given object and
68 * is registered with the given queue.
69 *
70 * <p> It is possible to create a phantom reference with a {@code null}
71 * queue, but such a reference is completely useless: Its {@code get}
72 * method will always return {@code null} and, since it does not have a queue,
73 * it will never be enqueued.
74 *
75 * @param referent the object the new phantom reference will refer to
76 * @param q the queue with which the reference is to be registered,
77 * or {@code null} if registration is not required
78 * @throws IllegalArgumentException if the referent is an instance of an
79 * {@link Class#isInlineClass() inlineClass}
80 */
81 public PhantomReference(T referent, ReferenceQueue<? super T> q) {
82 super(referent, q);
83 }
84
85 }
|