1/* 2 * Copyright (c) 2003, 2013, 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 26package java.lang.annotation; 27 28/** 29 * The common interface extended by all annotation types. Note that an 30 * interface that manually extends this one does <i>not</i> define 31 * an annotation type. Also note that this interface does not itself 32 * define an annotation type. 33 * 34 * More information about annotation types can be found in section 9.6 of 35 * <cite>The Java™ Language Specification</cite>. 36 * 37 * The {@link java.lang.reflect.AnnotatedElement} interface discusses 38 * compatibility concerns when evolving an annotation type from being 39 * non-repeatable to being repeatable. 40 * 41 * @author Josh Bloch 42 * @since 1.5 43 */ 44public interface Annotation { 45 /** 46 * Returns true if the specified object represents an annotation 47 * that is logically equivalent to this one. In other words, 48 * returns true if the specified object is an instance of the same 49 * annotation type as this instance, all of whose members are equal 50 * to the corresponding member of this annotation, as defined below: 51 * <ul> 52 * <li>Two corresponding primitive typed members whose values are 53 * {@code x} and {@code y} are considered equal if {@code x == y}, 54 * unless their type is {@code float} or {@code double}. 55 * 56 * <li>Two corresponding {@code float} members whose values 57 * are {@code x} and {@code y} are considered equal if 58 * {@code Float.valueOf(x).equals(Float.valueOf(y))}. 59 * (Unlike the {@code ==} operator, NaN is considered equal 60 * to itself, and {@code 0.0f} unequal to {@code -0.0f}.) 61 * 62 * <li>Two corresponding {@code double} members whose values 63 * are {@code x} and {@code y} are considered equal if 64 * {@code Double.valueOf(x).equals(Double.valueOf(y))}. 65 * (Unlike the {@code ==} operator, NaN is considered equal 66 * to itself, and {@code 0.0} unequal to {@code -0.0}.) 67 * 68 * <li>Two corresponding {@code String}, {@code Class}, enum, or 69 * annotation typed members whose values are {@code x} and {@code y} 70 * are considered equal if {@code x.equals(y)}. (Note that this 71 * definition is recursive for annotation typed members.) 72 * 73 * <li>Two corresponding array typed members {@code x} and {@code y} 74 * are considered equal if {@code Arrays.equals(x, y)}, for the 75 * appropriate overloading of {@link java.util.Arrays#equals}. 76 * </ul> 77 * 78 * @return true if the specified object represents an annotation 79 * that is logically equivalent to this one, otherwise false 80 */ 81 boolean equals(Object obj); 82 83 /** 84 * Returns the hash code of this annotation, as defined below: 85 * 86 * <p>The hash code of an annotation is the sum of the hash codes 87 * of its members (including those with default values), as defined 88 * below: 89 * 90 * The hash code of an annotation member is (127 times the hash code 91 * of the member-name as computed by {@link String#hashCode()}) XOR 92 * the hash code of the member-value, as defined below: 93 * 94 * <p>The hash code of a member-value depends on its type: 95 * <ul> 96 * <li>The hash code of a primitive value <i>{@code v}</i> is equal to 97 * <code><i>WrapperType</i>.valueOf(<i>v</i>).hashCode()</code>, where 98 * <i>{@code WrapperType}</i> is the wrapper type corresponding 99 * to the primitive type of <i>{@code v}</i> ({@link Byte}, 100 * {@link Character}, {@link Double}, {@link Float}, {@link Integer}, 101 * {@link Long}, {@link Short}, or {@link Boolean}). 102 * 103 * <li>The hash code of a string, enum, class, or annotation member-value 104 I <i>{@code v}</i> is computed as by calling 105 * <code><i>v</i>.hashCode()</code>. (In the case of annotation 106 * member values, this is a recursive definition.) 107 * 108 * <li>The hash code of an array member-value is computed by calling 109 * the appropriate overloading of 110 * {@link java.util.Arrays#hashCode(long[]) Arrays.hashCode} 111 * on the value. (There is one overloading for each primitive 112 * type, and one for object reference types.) 113 * </ul> 114 * 115 * @return the hash code of this annotation 116 */ 117 int hashCode(); 118 119 /** 120 * Returns a string representation of this annotation. The details 121 * of the representation are implementation-dependent, but the following 122 * may be regarded as typical: 123 * <pre> 124 * @com.acme.util.Name(first=Alfred, middle=E., last=Neuman) 125 * </pre> 126 * 127 * @return a string representation of this annotation 128 */ 129 String toString(); 130 131 /** 132 * Returns the annotation type of this annotation. 133 * @return the annotation type of this annotation 134 */ 135 Class<? extends Annotation> annotationType(); 136} 137