/*
 * @(#)$Id: ExpressionState.java,v 1.4 2001/05/01 18:13:02 Bear Exp $
 *
 * Copyright 2001 Sun Microsystems, Inc. All Rights Reserved.
 * 
 * This software is the proprietary information of Sun Microsystems, Inc.  
 * Use is subject to license terms.
 * 
 */
package com.sun.msv.reader;

import com.sun.msv.grammar.Expression;

/**
 * Base implementation for those states who read tags representing an expression.
 * 
 * <p>
 * Responsibility of derived classes are:
 * 
 * <ol>
 *  <li>if necessary, implement startSelf method to do something.
 *  <li>implement createChildState method, which is mandated by SimpleState.
 *  <li>implement makeExpression method to create Expression object
 *		as the outcome of parsing. This method is called at endElement.
 * </ol>
 * 
 * @author <a href="mailto:kohsuke.kawaguchi@eng.sun.com">Kohsuke KAWAGUCHI</a>
 */
public abstract class ExpressionState extends SimpleState
{
	protected void endSelf()
	{
		// creates a expression, then calls a hook of reader,
		Expression exp = reader.interceptExpression( this, makeExpression() );
		
		if( parentState!=null )
			// then finally pass it to the parent
			((ExpressionOwner)parentState).onEndChild(exp);
		
		// interceptExpression is a hook by reader.
		// it is used to implement handling of occurs attribute in RELAX.
		// application-defined reader can also do something useful for them here.

		super.endSelf();
	}
		
	/**
	 * This method is called from endElement method.
	 * Implementation has to provide Expression object that represents the content of
	 * this element.
	 */
	protected abstract Expression makeExpression();
}