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 * Copyright (c) 2005, 2017, Oracle and/or its affiliates. All rights reserved.

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

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 * 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.

 *

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package javax.management;

import java.lang.annotation.*;

/**

 * <p>Meta-annotation that describes how an annotation element relates

 * to a field in a {@link Descriptor}.  This can be the Descriptor for

 * an MBean, or for an attribute, operation, or constructor in an

 * MBean, or for a parameter of an operation or constructor.</p>

 *

 * <p>Consider this annotation for example:</p>

 *

 * <pre>

 * @Documented

 * @Target(ElementType.METHOD)

 * @Retention(RetentionPolicy.RUNTIME)

 * public @interface Units {

 *     <b>&#64;DescriptorKey("units")</b>

 *     String value();

 * }

 * </pre>

 *

 * <p>and this use of the annotation:</p>

 *

 * <pre>

 * public interface CacheControlMBean {

 *     <b>&#64;Units("bytes")</b>

 *     public long getCacheSize();

 * }

 * </pre>

 *

 * <p>When a Standard MBean is made from the {@code CacheControlMBean},

 * the usual rules mean that it will have an attribute called

 * {@code CacheSize} of type {@code long}.  The {@code @Units}

 * annotation, given the above definition, will ensure that the

 * {@link MBeanAttributeInfo} for this attribute will have a

 * {@code Descriptor} that has a field called {@code units} with

 * corresponding value {@code bytes}.</p>

 *

 * <p>Similarly, if the annotation looks like this:</p>

 *

 * <pre>

 * @Documented

 * @Target(ElementType.METHOD)

 * @Retention(RetentionPolicy.RUNTIME)

 * public @interface Units {

 *     <b>&#64;DescriptorKey("units")</b>

 *     String value();

 *

 *     <b>&#64;DescriptorKey("descriptionResourceKey")</b>

 *     String resourceKey() default "";

 *

 *     <b>&#64;DescriptorKey("descriptionResourceBundleBaseName")</b>

 *     String resourceBundleBaseName() default "";

 * }

 * </pre>

 *

 * <p>and it is used like this:</p>

 *

 * <pre>

 * public interface CacheControlMBean {

 *     <b>&#64;Units("bytes",

 *            resourceKey="bytes.key",

 *            resourceBundleBaseName="com.example.foo.MBeanResources")</b>

 *     public long getCacheSize();

 * }

 * </pre>

 *

 * <p>then the resulting {@code Descriptor} will contain the following

 * fields:</p>

 *

 * <table class="striped">

 * <caption style="display:none">Descriptor Fields</caption>

 * <thead>

 * <tr><th scope="col">Name</th><th scope="col">Value</th></tr>

 * </thead>

 * <tbody style="text-align:left">

 * <tr><th scope="row">units</th><td>"bytes"</td></tr>

 * <tr><th scope="row">descriptionResourceKey</th><td>"bytes.key"</td></tr>

 * <tr><th scope="row">descriptionResourceBundleBaseName</th>

 *     <td>"com.example.foo.MBeanResources"</td></tr>

 * </tbody>

 * </table>

 *

 * <p>An annotation such as {@code @Units} can be applied to:</p>

 *

 * <ul>

 * <li>a Standard MBean or MXBean interface;

 * <li>a method in such an interface;

 * <li>a parameter of a method in a Standard MBean or MXBean interface

 * when that method is an operation (not a getter or setter for an attribute);

 * <li>a public constructor in the class that implements a Standard MBean

 * or MXBean;

 * <li>a parameter in such a constructor.

 * </ul>

 *

 * <p>Other uses of the annotation are ignored.</p>

 *

 * <p>Interface annotations are checked only on the exact interface

 * that defines the management interface of a Standard MBean or an

 * MXBean, not on its parent interfaces.  Method annotations are

 * checked only in the most specific interface in which the method

 * appears; in other words, if a child interface overrides a method

 * from a parent interface, only {@code @DescriptorKey} annotations in

 * the method in the child interface are considered.

 *

 * <p>The Descriptor fields contributed in this way by different

 * annotations on the same program element must be consistent.  That

 * is, two different annotations, or two members of the same

 * annotation, must not define a different value for the same

 * Descriptor field.  Fields from annotations on a getter method must

 * also be consistent with fields from annotations on the

 * corresponding setter method.</p>

 *

 * <p>The Descriptor resulting from these annotations will be merged

 * with any Descriptor fields provided by the implementation, such as

 * the <a href="Descriptor.html#immutableInfo">{@code

 * immutableInfo}</a> field for an MBean.  The fields from the annotations

 * must be consistent with these fields provided by the implementation.</p>

 *

 * <p>An annotation element to be converted into a descriptor field

 * can be of any type allowed by the Java language, except an annotation

 * or an array of annotations.  The value of the field is derived from

 * the value of the annotation element as follows:</p>

 *

 * <table class="striped">

 * <caption style="display:none">Descriptor Field Types</caption>

 * <thead>

 * <tr><th scope="col">Annotation element</th><th scope="col">Descriptor field</th></tr>

 * </thead>

 * <tbody style="text-align:left">

 * <tr><th scope="row">Primitive value ({@code 5}, {@code false}, etc)</th>

 *     <td>Wrapped value ({@code Integer.valueOf(5)},

 *         {@code Boolean.FALSE}, etc)</td></tr>

 * <tr><th scope="row">Class constant (e.g. {@code Thread.class})</th>

 *     <td>Class name from {@link Class#getName()}

 *         (e.g. {@code "java.lang.Thread"})</td></tr>

 * <tr><th scope="row">Enum constant (e.g. {@link ElementType#FIELD})</th>

 *     <td>Constant name from {@link Enum#name()}

 *         (e.g. {@code "FIELD"})</td></tr>

 * <tr><th scope="row">Array of class constants or enum constants</th>

 *     <td>String array derived by applying these rules to each

 *         element</td></tr>

 * <tr><th scope="row">Value of any other type<br>

 *         ({@code String}, {@code String[]}, {@code int[]}, etc)</th>

 *     <td>The same value</td></tr>

 * </tbody>

 * </table>

 *

 * @since 1.6

 */

@Documented

@Retention(RetentionPolicy.RUNTIME)

@Target(ElementType.METHOD)

public @interface DescriptorKey {

    /**

     * Returns the descriptor key.

     * @return the descriptor key

     */

    String value();

}