/*
 * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package javax.xml.bind;

import javax.xml.namespace.QName;
import java.io.Serializable;

/**
 * <p>JAXB representation of an Xml Element.</p>
 *
 * <p>This class represents information about an Xml Element from both the element 
 * declaration within a schema and the element instance value within an xml document
 * with the following properties
 * <ul>
 *   <li>element's xml tag <b><tt>name</tt></b></li>
 *   <li><b><tt>value</tt></b> represents the element instance's atttribute(s) and content model</li>
 *   <li>element declaration's <b><tt>declaredType</tt></b> (<tt>xs:element @type</tt> attribute)</li>
 *   <li><b><tt>scope</tt></b> of element declaration</li>
 *   <li>boolean <b><tt>nil</tt></b> property. (element instance's <tt><b>xsi:nil</b></tt> attribute)</li>
 * </ul>
 * 
 * <p>The <tt>declaredType</tt> and <tt>scope</tt> property are the
 * JAXB class binding for the xml type definition.
 * </p>
 * 
 * <p><b><tt>Scope</tt></b> is either {@link GlobalScope} or the Java class representing the 
 * complex type definition containing the schema element declaration.
 * </p>
 * 
 * <p>There is a property constraint that if <b><tt>value</tt></b> is <tt>null</tt>, 
 * then <tt>nil</tt> must be <tt>true</tt>. The converse is not true to enable 
 * representing a nil element with attribute(s). If <tt>nil</tt> is true, it is possible 
 * that <tt>value</tt> is non-null so it can hold the value of the attributes 
 * associated with a nil element.
 * </p>
 * 
 * @author Kohsuke Kawaguchi, Joe Fialli
 * @since JAXB 2.0
 */

public class JAXBElement<T> implements Serializable {

    /** xml element tag name */
    final protected QName name;

    /** Java datatype binding for xml element declaration's type. */
    final protected Class<T> declaredType;

    /** Scope of xml element declaration representing this xml element instance.
     *  Can be one of the following values:
     *  - {@link GlobalScope} for global xml element declaration.
     *  - local element declaration has a scope set to the Java class 
     *     representation of complex type defintion containing
     *     xml element declaration. 
     */
    final protected Class scope;

    /** xml element value. 
        Represents content model and attributes of an xml element instance. */
    protected T value;

    /** true iff the xml element instance has xsi:nil="true". */
    protected boolean nil = false;

    /**
     * Designates global scope for an xml element.
     */
    public static final class GlobalScope {}

    /**
     * <p>Construct an xml element instance.</p>
     * 
     * @param name          Java binding of xml element tag name
     * @param declaredType  Java binding of xml element declaration's type
     * @param scope
     *      Java binding of scope of xml element declaration.
     *      Passing null is the same as passing <tt>GlobalScope.class</tt>
     * @param value
     *      Java instance representing xml element's value.
     * @see #getScope()
     * @see #isTypeSubstituted()
     */
    public JAXBElement(QName name, 
		       Class<T> declaredType, 
		       Class scope,
		       T value) {
        if(declaredType==null || name==null)
            throw new IllegalArgumentException();
        this.declaredType = declaredType;
        if(scope==null)     scope = GlobalScope.class;
        this.scope = scope;
        this.name = name;
        setValue(value);
    }

    /**
     * Construct an xml element instance.