trunk/bval-extras/src/main/java/org/apache/bval/extras/constraints/checkdigit/EAN13Validator.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.bval.extras.constraints.checkdigit;

/**
 * Modulus 10 <b>EAN-13</b> / <b>UPC</b> / <b>ISBN-13</b> Check Digit
 * calculation/validation.
 * <p>
 * Check digit calculation is based on <i>modulus 10</i> with digits in
 * an <i>odd</i> position (from right to left) being weighted 1 and <i>even</i>
 * position digits being weighted 3.
 * <p>
 * For further information see:
 * <ul>
 *   <li>EAN-13 - see
 *       <a href="http://en.wikipedia.org/wiki/European_Article_Number">Wikipedia -
 *       European Article Number</a>.</li>
 *   <li>UPC - see
 *       <a href="http://en.wikipedia.org/wiki/Universal_Product_Code">Wikipedia -
 *       Universal Product Code</a>.</li>
 *   <li>ISBN-13 - see
 *       <a href="http://en.wikipedia.org/wiki/ISBN">Wikipedia - International
 *       Standard Book Number (ISBN)</a>.</li>
 * </ul>
 */
public final class EAN13Validator
    extends ModulusValidator<EAN13> {

    /** weighting given to digits depending on their right position */
    private static final int[] POSITION_WEIGHT = new int[] {3, 1};

    public EAN13Validator() {
        super(10);
    }

    /**
     * <p>Calculates the <i>weighted</i> value of a character in the
     * code at a specified position.</p>
     *
     * <p>For EAN-13 (from right to left) <b>odd</b> digits are weighted
     * with a factor of <b>one</b> and <b>even</b> digits with a factor
     * of <b>three</b>.</p>
     *
     * {@inheritDoc}
     */
    @Override
    protected int weightedValue( int charValue, int leftPos, int rightPos )
            throws Exception {
        int weight = POSITION_WEIGHT[rightPos % 2];
        return (charValue * weight);
    }

}