/*
 * @(#)DescriptorKey.java	1.5 06/05/02
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

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>@DescriptorKey("units")</b>
 *     String value();
 * }
 * </pre>
 *
 * <p>and this use of the annotation:</p>
 *
 * <pre>
 * public interface CacheControlMBean {
 *     <b>@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}
 * attribute, 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>@DescriptorKey("units")</b>
 *     String value();
 *
 *     <b>@DescriptorKey("descriptionResourceKey")</b>
 *     String resourceKey() default "";
 *
 *     <b>@DescriptorKey("descriptionResourceBundleBaseName")</b>
 *     String resourceBundleBaseName() default "";
 * }
 * </pre>
 *
 * <p>and it is used like this:</p>
 *
 * <pre>
 * public interface CacheControlMBean {
 *     <b>@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 border="2">
 * <tr><th>Name</th><th>Value</th></tr>
 * <tr><td>units</td><td>"bytes"</td></tr>
 * <tr><td>descriptionResourceKey</td><td>"bytes.key"</td></tr>
 * <tr><td>descriptionResourceBundleBaseName</td>
 *     <td>"com.example.foo.MBeanResources"</td></tr>
 * </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>
 *