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The Java Persistence API (JPA) : a standard interface-based Java model abstraction of persistence, developed by the JCP.

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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.ANNOTATION_TYPE;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import static javax.persistence.FetchType.LAZY;

/**
 * Defines a collection of instances of a basic type or embeddable class. Must be specified if the collection
 * is to be mapped by means of a collection table.
 *
 *  *    Example:
 * 
 *    @Entity public class Person {
 *       @Id protected String ssn;
 *       protected String name;
 *       ...
 *       @ElementCollection
 *       protected Set<String> nickNames = new HashSet();
 *         ...
 *    }
 * 
 * @since Java Persistence 2.0
 */
@Target({ANNOTATION_TYPE, METHOD, FIELD})
@Retention(RUNTIME)
public @interface ElementCollection
{

    /**
     * (Optional) The basic or embeddable class that is the element type of the collection. This element is
     * optional only if the collection field or property is defined using Java generics, and must be specified
     * otherwise. It defaults to the paramterized type of the collection when defined using generics.
     * @return target class
     */
    Class targetClass() default void.class;

    /**
     * (Optional) Whether the collection should be lazily loaded or must be eagerly fetched. The EAGER
     * strategy is a requirement on the persistence provider runtime that the collection elements must be
     * eagerly fetched. The LAZY strategy is a hint to the persistence provider runtime.
     * @return fetch type
     */
    FetchType fetch() default LAZY;
}