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.io;
27
28 import java.io.ObjectOutput;
29 import java.io.ObjectInput;
30
31 /**
32 * Only the identity of the class of an Externalizable instance is
33 * written in the serialization stream and it is the responsibility
34 * of the class to save and restore the contents of its instances.
35 *
36 * The writeExternal and readExternal methods of the Externalizable
37 * interface are implemented by a class to give the class complete
38 * control over the format and contents of the stream for an object
39 * and its supertypes. These methods must explicitly
40 * coordinate with the supertype to save its state. These methods supersede
41 * customized implementations of writeObject and readObject methods.<br>
42 *
43 * Object Serialization uses the Serializable and Externalizable
44 * interfaces. Object persistence mechanisms can use them as well. Each
45 * object to be stored is tested for the Externalizable interface. If
46 * the object supports Externalizable, the writeExternal method is called. If the
47 * object does not support Externalizable and does implement
48 * Serializable, the object is saved using
49 * ObjectOutputStream. <br> When an Externalizable object is
50 * reconstructed, an instance is created using the public no-arg
51 * constructor, then the readExternal method called. Serializable
52 * objects are restored by reading them from an ObjectInputStream.<br>
53 *
54 * An Externalizable instance can designate a substitution object via
55 * the writeReplace and readResolve methods documented in the Serializable
56 * interface.<br>
57 *
58 * @see java.io.ObjectOutputStream
59 * @see java.io.ObjectInputStream
60 * @see java.io.ObjectOutput
61 * @see java.io.ObjectInput
62 * @see java.io.Serializable
63 * @since 1.1
64 */
65 public interface Externalizable extends java.io.Serializable {
66 /**
67 * The object implements the writeExternal method to save its contents
68 * by calling the methods of DataOutput for its primitive values or
69 * calling the writeObject method of ObjectOutput for objects, strings,
70 * and arrays.
71 *
72 * @serialData Overriding methods should use this tag to describe
73 * the data layout of this Externalizable object.
74 * List the sequence of element types and, if possible,
75 * relate the element to a public/protected field and/or
76 * method of this Externalizable class.
|
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.io;
27
28 import java.io.ObjectOutput;
29 import java.io.ObjectInput;
30
31 /**
32 * A {@code Serializable} class that fully implements its own protocol
33 * for reading and writing to a serialization stream.
34 * <p>
35 * Only the identity of the class of an {@code Externalizable} instance is
36 * written in the serialization stream and it is the responsibility
37 * of the class to save and restore the contents of its instances.
38 * The {@code writeExternal} and {@code readExternal} methods give the
39 * class complete control over the format and contents of the stream
40 * for an object and its supertypes. These methods must explicitly
41 * coordinate with the supertype to save its state. These methods supersede
42 * customized implementations of {@code writeObject} and {@code readObject}
43 * methods.
44 * <p>
45 * Object Serialization uses the {@code Serializable} and {@code Externalizable}
46 * interfaces. Object persistence mechanisms can use them as well. Each
47 * object to be stored is tested for the {@code Externalizable} interface. If
48 * the object supports {@code Externalizable}, the {@code writeExternal} method
49 * is called. If the object does not support {@code Externalizable} and does
50 * implement {@code Serializable}, the object is saved using
51 * {@code ObjectOutputStream}.
52 * <p>
53 * When an {@code Externalizable} object is reconstructed, an instance is
54 * created using the public no-arg constructor, then the
55 * {@code readExternal} method called.
56 * <p>
57 * An {@code Externalizable} instance can designate a substitution object via
58 * the {@code writeReplace} and {@code readResolve} methods documented in the
59 * {@link Serializable} interface.
60 * <p>
61 * Record classes can implement {@code Externalizable}, but it is ignored:
62 * instances will receive the same treatment as other {@code Serializable}
63 * instances, as defined by the
64 * <a href="{@docRoot}/../specs/serialization/serial-arch.html#serialization-of-records">
65 * <cite>Java Object Serialization Specification,</cite> Section 1.13,
66 * "Serialization of Records"</a>.
67 *
68 * <div class="preview-block">
69 * <div class="preview-comment">
70 * <p>{@linkplain Class#isValue Value classes} that are not records are
71 * permitted to implement {@code Externalizable}, but the class has no
72 * mutable fields, and so is unlikely to be able to properly implement
73 * the {@code readExternal} method. Instead, the {@code writeReplace}
74 * method should be used to designate an alternative object for
75 * serialization. At deserialization time, the alternative object can
76 * implement {@code readResolve} to construct the expected value class
77 * instance.
78 * </div>
79 * </div>
80 *
81 * @see java.io.ObjectOutputStream
82 * @see java.io.ObjectInputStream
83 * @see java.io.ObjectOutput
84 * @see java.io.ObjectInput
85 * @see java.io.Serializable
86 * @since 1.1
87 */
88 public interface Externalizable extends java.io.Serializable {
89 /**
90 * The object implements the writeExternal method to save its contents
91 * by calling the methods of DataOutput for its primitive values or
92 * calling the writeObject method of ObjectOutput for objects, strings,
93 * and arrays.
94 *
95 * @serialData Overriding methods should use this tag to describe
96 * the data layout of this Externalizable object.
97 * List the sequence of element types and, if possible,
98 * relate the element to a public/protected field and/or
99 * method of this Externalizable class.
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