    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 *      https://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 */
    017package org.apache.commons.validator.routines.checkdigit;
    018
    019/**
    020 * Modulus 10 <strong>EAN-13</strong> / <strong>UPC</strong> / <strong>ISBN-13</strong> Check Digit
    021 * calculation/validation.
    022 * <p>
    023 * Check digit calculation is based on <em>modulus 10</em> with digits in
    024 * an <em>odd</em> position (from right to left) being weighted 1 and <em>even</em>
    025 * position digits being weighted 3.
    026 * <p>
    027 * For further information see:
    028 * <ul>
    029 *   <li>EAN-13 - see
    030 *       <a href="https://en.wikipedia.org/wiki/European_Article_Number">Wikipedia -
    031 *       European Article Number</a>.</li>
    032 *   <li>UPC - see
    033 *       <a href="https://en.wikipedia.org/wiki/Universal_Product_Code">Wikipedia -
    034 *       Universal Product Code</a>.</li>
    035 *   <li>ISBN-13 - see
    036 *       <a href="https://en.wikipedia.org/wiki/ISBN">Wikipedia - International
    037 *       Standard Book Number (ISBN)</a>.</li>
    038 * </ul>
    039 *
    040 * @since 1.4
    041 */
    042public final class EAN13CheckDigit extends ModulusCheckDigit {
    043
    044    private static final long serialVersionUID = 1726347093230424107L;
    045
    046    /** Singleton EAN-13 Check Digit instance */
    047    public static final CheckDigit EAN13_CHECK_DIGIT = new EAN13CheckDigit();
    048
    049    /** Weighting given to digits depending on their right position */
    050    private static final int[] POSITION_WEIGHT = {3, 1};
    051
    052    /**
    053     * Constructs a modulus 10 Check Digit routine for EAN/UPC.
    054     */
    055    public EAN13CheckDigit() {
    056    }
    057
    058    /**
    059     * <p>Calculates the <em>weighted</em> value of a character in the
    060     * code at a specified position.</p>
    061     *
    062     * <p>For EAN-13 (from right to left) <strong>odd</strong> digits are weighted
    063     * with a factor of <strong>one</strong> and <strong>even</strong> digits with a factor
    064     * of <strong>three</strong>.</p>
    065     *
    066     * @param charValue The numeric value of the character.
    067     * @param leftPos The position of the character in the code, counting from left to right
    068     * @param rightPos The position of the character in the code, counting from right to left
    069     * @return The weighted value of the character.
    070     */
    071    @Override
    072    protected int weightedValue(final int charValue, final int leftPos, final int rightPos) {
    073        return charValue * POSITION_WEIGHT[rightPos % 2];
    074    }
    075}