jaxb-api/src/main/java/jakarta/xml/bind/annotation/XmlRootElement.java

/*
 * Copyright (c) 2004, 2020 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0, which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package jakarta.xml.bind.annotation;

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

import static java.lang.annotation.RetentionPolicy.RUNTIME;
import static java.lang.annotation.ElementType.TYPE;

/**
 * Maps a class or an enum type to an XML element.
 *
 * <p> <b>Usage</b> </p>
 * <p>
 * The &#64;XmlRootElement annotation can be used with the following program
 * elements: 
 * <ul> 
 *   <li> a top level class </li>
 *   <li> an enum type </li>
 * </ul>
 *
 * <p>See "Package Specification" in jakarta.xml.bind.package javadoc for
 * additional common information.</p>
 * 
 * <p>
 * When a top level class or an enum type is annotated with the 
 * &#64;XmlRootElement annotation, then its value is represented 
 * as XML element in an XML document.
 *
 * <p> This annotation can be used with the following annotations:
 * {@link XmlType}, {@link XmlEnum}, {@link XmlAccessorType}, 
 * {@link XmlAccessorOrder}.
 * </p>

 * <p>
 * <b>Example 1: </b> Associate an element with XML Schema type
 * <pre>
 *     // Example: Code fragment
 *     &#64;XmlRootElement
 *     class Point {
 *        int x;
 *        int y;
 *        Point(int _x,int _y) {x=_x;y=_y;}
 *     }
 * </pre>
 *
 * <pre>
 *     //Example: Code fragment corresponding to XML output
 *     marshal( new Point(3,5), System.out);
 * </pre>
 *
 * <pre>{@code
 * 
 *     <!-- Example: XML output -->
 *     <point>
 *       <x> 3 </x>
 *       <y> 5 </y>
 *     </point>
 * }</pre>
 *
 * The annotation causes an global element declaration to be produced
 * in the schema. The global element declaration is associated with
 * the XML schema type to which the class is mapped.
 *
 * <pre>{@code
 * 
 *     <!-- Example: XML schema definition -->
 *     <xs:element name="point" type="point"/>
 *     <xs:complexType name="point">
 *       <xs:sequence>
 *         <xs:element name="x" type="xs:int"/>
 *         <xs:element name="y" type="xs:int"/>
 *       </xs:sequence>
 *     </xs:complexType>
 * }</pre>
 *
 * <p>
 *
 * <b>Example 2: Orthogonality to type inheritance </b>
 * 
 * <p>
 * An element declaration annotated on a type is not inherited by its
 * derived types. The following example shows this.
 * <pre>
 *     // Example: Code fragment
 *     &#64;XmlRootElement
 *     class Point3D extends Point {
 *         int z;
 *         Point3D(int _x,int _y,int _z) {super(_x,_y);z=_z;}
 *     }
 *
 *     //Example: Code fragment corresponding to XML output * 
 *     marshal( new Point3D(3,5,0), System.out );
 * {@code
 * 
 *     <!-- Example: XML output -->
 *     <!-- The element name is point3D not point -->
 *     <point3D>
 *       <x>3</x>
 *       <y>5</y>
 *       <z>0</z>
 *     </point3D>
 *
 *     <!-- Example: XML schema definition -->
 *     <xs:element name="point3D" type="point3D"/>
 *     <xs:complexType name="point3D">
 *       <xs:complexContent>
 *         <xs:extension base="point">
 *           <xs:sequence>
 *             <xs:element name="z" type="xs:int"/>
 *           </xs:sequence>
 *         </xs:extension>
 *       </xs:complexContent>
 *     </xs:complexType>
 * }</pre>
 *
 * <b>Example 3: </b> Associate a global element with XML Schema type
 * to which the class is mapped.
 * <pre>
 *     //Example: Code fragment
 *     &#64;XmlRootElement(name="PriceElement")
 *     public class USPrice {
 *         &#64;XmlElement
 *         public java.math.BigDecimal price;
 *     }
 * {@code
 * 
 *     <!-- Example: XML schema definition -->
 *     <xs:element name="PriceElement" type="USPrice"/>
 *     <xs:complexType name="USPrice">
 *       <xs:sequence>
 *         <xs:element name="price" type="xs:decimal"/>
 *       </sequence>
 *     </xs:complexType>
 * }</pre>
 *
 * @author Sekhar Vajjhala, Sun Microsystems, Inc.
 * @since 1.6, JAXB 2.0
 */
@Retention(RUNTIME)
@Target({TYPE})
public @interface XmlRootElement {
    /**
     * namespace name of the XML element.
     * <p>
     * If the value is "##default", then the XML namespace name is derived
     * from the package of the class ( {@link XmlSchema} ). If the
     * package is unnamed, then the XML namespace is the default empty
     * namespace.
     */
    String namespace() default "##default";

    /**
     * local name of the XML element.
     * <p>
     * If the value is "##default", then the name is derived from the
     * class name. 
     *
     */
    String name() default "##default";

}