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Clean-room definition of JPA APIs intended for use in developing Hibernate JPA implementation. See README.md for details

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/*
 * Copyright (c) 2008, 2009, 2011 Oracle, Inc. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0
 * which accompanies this distribution.  The Eclipse Public License is available
 * at http://www.eclipse.org/legal/epl-v10.html and the Eclipse Distribution License
 * is available at http://www.eclipse.org/org/documents/edl-v10.php.
 */
package javax.persistence;

import java.lang.annotation.Retention;
import java.lang.annotation.Target;

import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

/**
 * Specifies the type of the map key for associations of type
 * java.util.Map.  The map key can be a basic type, an
 * embeddable class, or an entity. If the map is specified using Java
 * generics, the MapKeyClass annotation and associated
 * type need not be specified; otherwise they must be specified.
 *
 *  The MapKeyClass annotation is used in conjunction
 * with ElementCollection or one of the collection-valued
 * relationship annotations (OneToMany or ManyToMany).
 * The MapKey annotation is not used when
 * MapKeyClass is specified and vice versa.
 *
 * 
 *
 *    Example 1:
 *
 *    @Entity
 *    public class Item {
 *       @Id int id;
 *       ...
 *       @ElementCollection(targetClass=String.class)
 *       @MapKeyClass(String.class)
 *       Map images;  // map from image name to image filename
 *       ...
 *    }
 *
 *    Example 2:
 *
 *    // MapKeyClass and target type of relationship can be defaulted
 *
 *    @Entity
 *    public class Item {
 *       @Id int id;
 *       ...
 *       @ElementCollection
 *       Map<String, String> images;
 *        ...
 *     }
 *
 *     Example 3:
 *
 *     @Entity
 *     public class Company {
 *        @Id int id;
 *        ...
 *        @OneToMany(targetEntity=com.example.VicePresident.class)
 *        @MapKeyClass(com.example.Division.class)
 *        Map organization;
 *     }
 *
 *     Example 4:
 *
 *     // MapKeyClass and target type of relationship are defaulted
 *
 *     @Entity
 *     public class Company {
 *        @Id int id;
 *        ...
 *        @OneToMany
 *        Map<Division, VicePresident> organization;
 *     }
 *
 * 
 * @see ElementCollection
 * @see OneToMany
 * @see ManyToMany
 * @since Java Persistence 2.0
 */

@Target( { METHOD, FIELD })
@Retention(RUNTIME)
public @interface MapKeyClass {
	/**(Required) The type of the map key.*/
	Class value();
}