/*
 * Copyright (c) 2004, 2018 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 javax.xml.bind;

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

JAXB representation of an Xml Element.
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

  
element's xml tag name
  
value represents the element instance's atttribute(s) and content model
  
element declaration's declaredType (xs:element @type attribute)
  
scope of element declaration
  
boolean nil property. (element instance's xsi:nil attribute)

The declaredType and scope property are the JAXB class binding for the xml type definition. 
Scope is either GlobalScope or the Java class representing the complex type definition containing the schema element declaration. 
There is a property constraint that if value is null, then nil must be true. The converse is not true to enable representing a nil element with attribute(s). If nil is true, it is possible that value is non-null so it can hold the value of the attributes associated with a nil element. 
Author:
Kohsuke Kawaguchi, Joe Fialli
Since:
1.6, JAXB 2.0/**
 * <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>{@code name}</b></li>
 *   <li><b>{@code value}</b> represents the element instance's atttribute(s) and content model</li>
 *   <li>element declaration's <b>{@code declaredType}</b> ({@code xs:element @type} attribute)</li>
 *   <li><b>{@code scope}</b> of element declaration</li>
 *   <li>boolean <b>{@code nil}</b> property. (element instance's <b>{@code xsi:nil}</b> attribute)</li>
 * </ul>
 * 
 * <p>The {@code declaredType} and {@code scope} property are the
 * JAXB class binding for the xml type definition.
 * </p>
 * 
 * <p><b>{@code Scope}</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>{@code value}</b> is {@code null},
 * then {@code nil} must be {@code true}. The converse is not true to enable
 * representing a nil element with attribute(s). If {@code nil} is true, it is possible
 * that {@code value} is non-null so it can hold the value of the attributes
 * associated with a nil element.
 * </p>
 * 
 * @author Kohsuke Kawaguchi, Joe Fialli
 * @since 1.6, JAXB 2.0
 */

public class JAXBElement<T> implements Serializable {

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

    
Java datatype binding for xml element declaration's type. /** 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: - 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. /** 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. /** 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". /** true iff the xml element instance has xsi:nil="true". */
    protected boolean nil = false;

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

    
Construct an xml element instance.
Params:
name –          Java binding of xml element tag name
declaredType –  Java binding of xml element declaration's type
scope –  Java binding of scope of xml element declaration. Passing null is the same as passing GlobalScope.class
value – 
     Java instance representing xml element's value.
See Also:
getScope()
isTypeSubstituted()/**
     * <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 {@code GlobalScope.class}
     * @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. This is just a convenience method for new JAXBElement(name,declaredType,GlobalScope.class,value) /**
     * Construct an xml element instance.
     *
     * This is just a convenience method for {@code new JAXBElement(name,declaredType,GlobalScope.class,value)}
     */
    public JAXBElement(QName name, Class<T> declaredType, T value ) {
        this(name,declaredType,GlobalScope.class,value);
    }

    
Returns the Java binding of the xml element declaration's type attribute.
/**
     * Returns the Java binding of the xml element declaration's type attribute.
     */
    public Class<T> getDeclaredType() {
        return declaredType;
    }

    
Returns the xml element tag name.
/**
     * Returns the xml element tag name.
     */
    public QName getName() {
        return name;
    }

    
Set the content model and attributes of this xml element.
When this property is set to null, isNil() must by true. Details of constraint are described at isNil().
See Also:
isTypeSubstituted()/**
     * <p>Set the content model and attributes of this xml element.</p>
     *
     * <p>When this property is set to {@code null}, {@code isNil()} must by {@code true}.
     *    Details of constraint are described at {@link #isNil()}.</p>
     *
     * @see #isTypeSubstituted()
     */
    public void setValue(T t) {
        this.value = t;
    }

    
Return the content model and attribute values for this element.
See isNil() for a description of a property constraint when this value is null
/**
     * <p>Return the content model and attribute values for this element.</p>
     * 
     * <p>See {@link #isNil()} for a description of a property constraint when
     * this value is {@code null}</p>
     */
    public T getValue() {
        return value;
    }

    
Returns scope of xml element declaration.
See Also:
isGlobalScope()
Returns:
GlobalScope.class if this element is of global scope./**
     * Returns scope of xml element declaration.
     *
     * @see #isGlobalScope()
     * @return {@code GlobalScope.class} if this element is of global scope.
     */
    public Class getScope() {
        return scope;
    }
    
    
Returns true iff this element instance content model is nil.
This property always returns true when getValue() is null. Note that the converse is not true, when this property is true, getValue() can contain a non-null value for attribute(s). It is valid for a nil xml element to have attribute(s).
/**
     * <p>Returns {@code true} iff this element instance content model
     * is nil.</p>
     *
     * <p>This property always returns {@code true} when {@link #getValue()} is null.
     * Note that the converse is not true, when this property is {@code true},
     * {@link #getValue()} can contain a non-null value for attribute(s). It is
     * valid for a nil xml element to have attribute(s).</p>
     */
    public boolean isNil() {
        return (value == null) || nil;
    }

    
Set whether this element has nil content.
See Also:
isNil()/**
     * <p>Set whether this element has nil content.</p>
     * 
     * @see #isNil()
     */
    public void setNil(boolean value) {
        this.nil = value;
    }
    
    /* Convenience methods  
     * (Not necessary but they do unambiguously conceptualize 
     *  the rationale behind this class' fields.)
     */

    
Returns true iff this xml element declaration is global.
/**
     * Returns true iff this xml element declaration is global.
     */
    public boolean isGlobalScope() {
        return this.scope == GlobalScope.class;
    }

    
Returns true iff this xml element instance's value has a different
type than xml element declaration's declared type.
/**
     * Returns true iff this xml element instance's value has a different
     * type than xml element declaration's declared type.
     */
    public boolean isTypeSubstituted() {
        if(value==null)     return false;
        return value.getClass() != declaredType;
    }

    private static final long serialVersionUID = 1L;
}