/* NullType Copyright (C) 1999-2002 Jochen Hoenicke.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation; either version 2, or (at your option)
 * any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this program; see the file COPYING.LESSER.  If not, write to
 * the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
 *
 * $Id$
 */

package jode.type;
import jode.AssertError;

/**
 * This class represents the NullType.  The null type is special as it
 * may only occur as top type in a range type.  It represents the type
 * of the null constant, which may be casted to any object. <br>
 *
 * Question: Should we replace tUObject = tRange(tObject, tNull) by tNull?
 * Question2: if not, should null have type tNull?
 *
 * @author Jochen Hoenicke 
 */
public class NullType extends ReferenceType {
    public NullType() {
	super(TC_NULL);
    }

    public Type getSubType() {
	return this;
    }

    public Type createRangeType(ReferenceType bottomType) {
	return tRange(bottomType, this);
    }

    /**
     * Returns the generalized type of this and type.  We have two
     * classes and multiple interfaces.  The result should be the
     * object that is the the super class of both objects and all
     * interfaces, that one class or interface of each type 
     * implements.  
     */
    public Type getGeneralizedType(Type type) {
	if (type.typecode == TC_RANGE)
	    type = ((RangeType) type).getTop();
	return type;
    }

    /**
     * Returns the specialized type of this and type.
     * We have two classes and multiple interfaces.  The result 
     * should be the object that extends both objects
     * and the union of all interfaces.
     */
    public Type getSpecializedType(Type type) {
	if (type.typecode == TC_RANGE)
	    type = ((RangeType) type).getBottom();
	return type;
    }

    public String toString() {
	return "tNull";
    }
}