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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   *
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
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24   */
25  
26  package 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&trade; 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   */
44  public 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       *    <tt>x</tt> and <tt>y</tt> are considered equal if <tt>x == y</tt>,
54       *    unless their type is <tt>float</tt> or <tt>double</tt>.
55       *
56       *    <li>Two corresponding <tt>float</tt> members whose values
57       *    are <tt>x</tt> and <tt>y</tt> are considered equal if
58       *    <tt>Float.valueOf(x).equals(Float.valueOf(y))</tt>.
59       *    (Unlike the <tt>==</tt> operator, NaN is considered equal
60       *    to itself, and <tt>0.0f</tt> unequal to <tt>-0.0f</tt>.)
61       *
62       *    <li>Two corresponding <tt>double</tt> members whose values
63       *    are <tt>x</tt> and <tt>y</tt> are considered equal if
64       *    <tt>Double.valueOf(x).equals(Double.valueOf(y))</tt>.
65       *    (Unlike the <tt>==</tt> operator, NaN is considered equal
66       *    to itself, and <tt>0.0</tt> unequal to <tt>-0.0</tt>.)
67       *
68       *    <li>Two corresponding <tt>String</tt>, <tt>Class</tt>, enum, or
69       *    annotation typed members whose values are <tt>x</tt> and <tt>y</tt>
70       *    are considered equal if <tt>x.equals(y)</tt>.  (Note that this
71       *    definition is recursive for annotation typed members.)
72       *
73       *    <li>Two corresponding array typed members <tt>x</tt> and <tt>y</tt>
74       *    are considered equal if <tt>Arrays.equals(x, y)</tt>, 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 <tt><i>v</i></tt> is equal to
97       *     <tt><i>WrapperType</i>.valueOf(<i>v</i>).hashCode()</tt>, where
98       *     <tt><i>WrapperType</i></tt> is the wrapper type corresponding
99       *     to the primitive type of <tt><i>v</i></tt> ({@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     <tt><i>v</i></tt> is computed as by calling
105      *     <tt><i>v</i>.hashCode()</tt>.  (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      *   &#064;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 }