1 /* 2 * Copyright (c) 2018, 2020, 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.io; 27 28 import java.lang.annotation.*; 29 30 /** 31 * Indicates that an annotated field or method is part of the {@linkplain 32 * Serializable serialization mechanism} defined by the 33 * <cite>Java Object Serialization Specification</cite>. This 34 * annotation type is intended to allow compile-time checking of 35 * serialization-related declarations, analogous to the checking 36 * enabled by the {@link java.lang.Override} annotation type to 37 * validate method overriding. {@code Serializable} classes are encouraged to 38 * use {@code @Serial} annotations to help a compiler catch 39 * mis-declared serialization-related fields and methods, 40 * mis-declarations that may otherwise be difficult to detect. 41 * 42 * <p>Specifically, annotations of this type should be 43 * applied to serialization-related methods and fields in classes 44 * declared to be {@code Serializable}. The five serialization-related 45 * methods are: 46 * 47 * <ul> 48 * <li>{@code private void writeObject(java.io.ObjectOutputStream stream) throws IOException} 49 * <li>{@code private void readObject(java.io.ObjectInputStream stream) throws IOException, ClassNotFoundException} 50 * <li>{@code private void readObjectNoData() throws ObjectStreamException} 51 * <li><i>ANY-ACCESS-MODIFIER</i> {@code Object writeReplace() throws ObjectStreamException} 52 * <li><i>ANY-ACCESS-MODIFIER</i> {@code Object readResolve() throws ObjectStreamException} 53 * </ul> 54 * 55 * The two serialization-related fields are: 56 * 57 * <ul> 58 * <li>{@code private static final ObjectStreamField[] serialPersistentFields} 59 * <li>{@code private static final long serialVersionUID} 60 * </ul> 61 * 62 * Compilers are encouraged to validate that a method or field marked with a 63 * {@code @Serial} annotation is one of the defined serialization-related 64 * methods or fields declared in a meaningful context and issue a warning 65 * if that is not the case. 66 * 67 * <p>It is a semantic error to apply this annotation to other fields or methods, including: 68 * <ul> 69 * <li>fields or methods in a class that is not {@code Serializable} 70 * 71 * <li>fields or methods of the proper structural declaration, but in 72 * a type where they are ineffectual. For example, {@code enum} types 73 * are defined to have a {@code serialVersionUID} of {@code 0L} so a 74 * {@code serialVersionUID} field declared in an {@code enum} type is 75 * ignored. The five serialization-related methods identified above 76 * are likewise ignored for an {@code enum} type. 77 * 78 * <li>in a class that is {@code Externalizable}: 79 * <ul> 80 * <li> method declarations of {@code writeObject}, {@code 81 * readObject}, and {@code readObjectNoData} 82 * 83 * <li>a field declaration for {@code serialPersistentFields} 84 * </ul> 85 * 86 * While the {@code Externalizable} interface extends {@code 87 * Serializable}, the three methods and one field above are 88 * <em>not</em> used for externalizable classes. 89 * 90 * </ul> 91 * 92 * Note that serialization mechanism accesses its designated fields 93 * and methods reflectively and those fields and methods may appear 94 * otherwise unused in a {@code Serializable} class. 95 * 96 * @see Serializable 97 * @see Externalizable 98 * @since 14 99 */ 100 @Target({ElementType.METHOD, ElementType.FIELD}) 101 @Retention(RetentionPolicy.SOURCE) 102 public @interface Serial {} 103