expressionfunctiondifference.java

這是一個油Java實作的資料庫系統 是個入門的好材料

/* =============================================================
 * SmallSQL : a free Java DBMS library for the Java(tm) platform
 * =============================================================
 *
 * (C) Copyright 2004-2006, by Volker Berlin.
 *
 * Project Info:  http://www.smallsql.de/
 *
 * This library 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 2.1 of the License, or 
 * (at your option) any later version.
 *
 * This library 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 library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, 
 * USA.  
 *
 * [Java is a trademark or registered trademark of Sun Microsystems, Inc. 
 * in the United States and other countries.]
 *
 * ---------------
 * ExpressionFunctionDifference.java
 * ---------------
 * Author: Volker Berlin
 * 
 * Created on 24.06.2006
 */
package smallsql.database;


/**
 * @author Volker Berlin
 */
final class ExpressionFunctionDifference extends ExpressionFunctionReturnInt {


	final int getFunction() {
		return SQLTokenizer.DIFFERENCE;
	}


    boolean isNull() throws Exception {
        return param1.isNull() || param2.isNull();
    }


	final int getInt() throws Exception {
        if(isNull()) return 0;
		String str1 = ExpressionFunctionSoundex.getString(param1.getString());
        String str2 = ExpressionFunctionSoundex.getString(param2.getString());
        int diff = 0;
        for(int i=0; i<4; i++){
            if(str1.charAt(i) == str2.charAt(i)){
                diff++;
            }
        }
		return diff;
	}
}