MathParser.java

/*
 * This file is part of jHaushalt.
 * jHaushalt is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 * jHaushalt 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 General Public License for more details.
 * You should have received a copy of the GNU General Public License
 * along with jHaushalt; if not, see <http://www.gnu.org/licenses/>.
 * (C)opyright 2002-2010 Dr. Lars H. Hahn
 */

package haushalt.daten;

import java.text.NumberFormat;
import java.util.logging.Logger;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Parst einen String mit mehreren Zahlen und addiert diese.
 * 
 * @author Kay Ruhland
 * @version 2.6/2009.05.17
 * @since 2.6
 */

public class MathParser {

	private static final Logger LOGGER = Logger.getLogger(MathParser.class.getName());
	private final NumberFormat nf;

	MathParser() {
		this.nf = NumberFormat.getInstance();
	}

	MathParser(final NumberFormat nf) {
		this.nf = nf;
	}

	/**
	 * Bildet die Summe aus mehreren Zahlen. Bei einem '-' wird die Zahl
	 * als negative Zahl interpretiert und somit vom Ergebnis abgezogen.
	 * 
	 * @param expr
	 *            (" 5€ - 3,0")
	 * @return (2.0)
	 */
	public double parseExpr(final String expr) {
		final String operatoren = "+-";
		double res = 0.0;

		final Pattern p = Pattern.compile("[" + operatoren + "]{0,1}\\s*\\d+[,\\.]{0,1}\\d*");
		final Matcher m = p.matcher(expr);

		while (m.find()) {
			String sVal = m.group().replace(" ", "");
			if (sVal.startsWith("+")) {
				sVal = sVal.substring(1);
			}
			try {
				res += this.nf.parse(sVal).doubleValue();
			}
			catch (final java.text.ParseException e) {
				return 0.0;
			}
		}

		return res;
	}

	public static void main(final String[] args) {
		final NumberFormat nf = NumberFormat.getInstance();
		nf.setMinimumFractionDigits(2);
		nf.setMaximumFractionDigits(2);

		final MathParser mp = new MathParser(nf);
		// LOGGER.info("=  - 123,2 -4,1 CHF + *0,3€ 0,5$")
		// );
		LOGGER.info("" + mp.parseExpr("3.754,15"));
	}
}