001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.apache.commons.validator.routines.checkdigit;
018    
019    import java.io.Serializable;
020    
021    /**
022     * Modulus 10 <b>EAN-13</b> / <b>UPC</b> / <b>ISBN-13</b> Check Digit
023     * calculation/validation.
024     * <p>
025     * Check digit calculation is based on <i>modulus 10</i> with digits in
026     * an <i>odd</i> position (from right to left) being weighted 1 and <i>even</i>
027     * position digits being weighted 3.
028     * <p>
029     * For further information see:
030     * <ul>
031     *   <li>EAN-13 - see 
032     *       <a href="http://en.wikipedia.org/wiki/European_Article_Number">Wikipedia - 
033     *       European Article Number</a>.</li>
034     *   <li>UPC - see
035     *       <a href="http://en.wikipedia.org/wiki/Universal_Product_Code">Wikipedia -
036     *       Universal Product Code</a>.</li>
037     *   <li>ISBN-13 - see 
038     *       <a href="http://en.wikipedia.org/wiki/ISBN">Wikipedia - International
039     *       Standard Book Number (ISBN)</a>.</li>
040     * </ul>
041     *
042     * @version $Revision: 493905 $ $Date: 2007-01-08 03:11:38 +0100 (Mo, 08. Jan 2007) $
043     * @since Validator 1.4
044     */
045    public final class EAN13CheckDigit extends ModulusCheckDigit implements Serializable {
046    
047        /** Singleton EAN-13 Check Digit instance */
048        public static final CheckDigit INSTANCE = new EAN13CheckDigit();
049    
050        /** weighting given to digits depending on their right position */
051        private static final int[] POSITION_WEIGHT = new int[] {3, 1};
052    
053        /**
054         * Construct a modulus 10 Check Digit routine for EAN/UPC.
055         */
056        public EAN13CheckDigit() {
057            super(10);
058        }
059    
060        /**
061         * <p>Calculates the <i>weighted</i> value of a character in the
062         * code at a specified position.</p>
063         *
064         * <p>For EAN-13 (from right to left) <b>odd</b> digits are weighted
065         * with a factor of <b>one</b> and <b>even</b> digits with a factor
066         * of <b>three</b>.</p>
067         *
068         * @param charValue The numeric value of the character.
069         * @param leftPos The position of the character in the code, counting from left to right 
070         * @param rightPos The positionof the character in the code, counting from right to left
071         * @return The weighted value of the character.
072         */
073        protected int weightedValue(int charValue, int leftPos, int rightPos) {
074            int weight = POSITION_WEIGHT[rightPos % 2];
075            return (charValue * weight);
076        }
077    }