/*

 * Copyright (c) 2003, 2009, Oracle and/or its affiliates. All rights reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

package java.lang.annotation;

/**

 * The common interface extended by all annotation types.  Note that an

 * interface that manually extends this one does <i>not</i> define

 * an annotation type.  Also note that this interface does not itself

 * define an annotation type.

 *

 * More information about annotation types can be found in section 9.6 of

 * <cite>The Java&trade; Language Specification</cite>.

 *

 * @author  Josh Bloch

 * @since   1.5

 */

public interface Annotation {

    /**

     * Returns true if the specified object represents an annotation

     * that is logically equivalent to this one.  In other words,

     * returns true if the specified object is an instance of the same

     * annotation type as this instance, all of whose members are equal

     * to the corresponding member of this annotation, as defined below:

     * <ul>

     *    <li>Two corresponding primitive typed members whose values are

     *    <tt>x</tt> and <tt>y</tt> are considered equal if <tt>x == y</tt>,

     *    unless their type is <tt>float</tt> or <tt>double</tt>.

     *

     *    <li>Two corresponding <tt>float</tt> members whose values

     *    are <tt>x</tt> and <tt>y</tt> are considered equal if

     *    <tt>Float.valueOf(x).equals(Float.valueOf(y))</tt>.

     *    (Unlike the <tt>==</tt> operator, NaN is considered equal

     *    to itself, and <tt>0.0f</tt> unequal to <tt>-0.0f</tt>.)

     *

     *    <li>Two corresponding <tt>double</tt> members whose values

     *    are <tt>x</tt> and <tt>y</tt> are considered equal if

     *    <tt>Double.valueOf(x).equals(Double.valueOf(y))</tt>.

     *    (Unlike the <tt>==</tt> operator, NaN is considered equal

     *    to itself, and <tt>0.0</tt> unequal to <tt>-0.0</tt>.)

     *

     *    <li>Two corresponding <tt>String</tt>, <tt>Class</tt>, enum, or

     *    annotation typed members whose values are <tt>x</tt> and <tt>y</tt>

     *    are considered equal if <tt>x.equals(y)</tt>.  (Note that this

     *    definition is recursive for annotation typed members.)

     *

     *    <li>Two corresponding array typed members <tt>x</tt> and <tt>y</tt>

     *    are considered equal if <tt>Arrays.equals(x, y)</tt>, for the

     *    appropriate overloading of {@link java.util.Arrays#equals}.

     * </ul>

     *

     * @return true if the specified object represents an annotation

     *     that is logically equivalent to this one, otherwise false

     */

    boolean equals(Object obj);

    /**

     * Returns the hash code of this annotation, as defined below:

     *

     * <p>The hash code of an annotation is the sum of the hash codes

     * of its members (including those with default values), as defined

     * below:

     *

     * The hash code of an annotation member is (127 times the hash code

     * of the member-name as computed by {@link String#hashCode()}) XOR

     * the hash code of the member-value, as defined below:

     *

     * <p>The hash code of a member-value depends on its type:

     * <ul>

     * <li>The hash code of a primitive value <tt><i>v</i></tt> is equal to

     *     <tt><i>WrapperType</i>.valueOf(<i>v</i>).hashCode()</tt>, where

     *     <tt><i>WrapperType</i></tt> is the wrapper type corresponding

     *     to the primitive type of <tt><i>v</i></tt> ({@link Byte},

     *     {@link Character}, {@link Double}, {@link Float}, {@link Integer},

     *     {@link Long}, {@link Short}, or {@link Boolean}).

     *

     * <li>The hash code of a string, enum, class, or annotation member-value

     I     <tt><i>v</i></tt> is computed as by calling

     *     <tt><i>v</i>.hashCode()</tt>.  (In the case of annotation

     *     member values, this is a recursive definition.)

     *

     * <li>The hash code of an array member-value is computed by calling

     *     the appropriate overloading of

     *     {@link java.util.Arrays#hashCode(long[]) Arrays.hashCode}

     *     on the value.  (There is one overloading for each primitive

     *     type, and one for object reference types.)

     * </ul>

     *

     * @return the hash code of this annotation

     */

    int hashCode();

    /**

     * Returns a string representation of this annotation.  The details

     * of the representation are implementation-dependent, but the following

     * may be regarded as typical:

     * <pre>

     *   @com.acme.util.Name(first=Alfred, middle=E., last=Neuman)

     * </pre>

     *

     * @return a string representation of this annotation

     */

    String toString();

    /**

     * Returns the annotation type of this annotation.

     */

    Class<? extends Annotation> annotationType();

}