trunk/bval-extras/src/main/java/org/apache/bval/extras/constraints/checkdigit/ISBN10Validator.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 11 <b>ISBN-10</b> Check Digit calculation/validation.
 * <p>
 * ISBN-10 Numbers are a numeric code except for the last (check) digit
 * which can have a value of "X".
 * <p>
 * Check digit calculation is based on <i>modulus 11</i> with digits being weighted
 * based by their position, from right to left  with the first digit being weighted
 * 1, the second 2 and so on. If the check digit is calculated as "10" it is converted
 * to "X".
 * <p>
 * <b>N.B.</b> From 1st January 2007 the book industry will start to use a new 13 digit
 * ISBN number (rather than this 10 digit ISBN number) which uses the EAN-13 / UPC
 * (see {@link EAN13CheckDigit}) standard.
 * <p>
 * For further information see:
 * <ul>
 *   <li><a href="http://en.wikipedia.org/wiki/ISBN">Wikipedia - International
 *       Standard Book Number (ISBN)</a>.</li>
 *   <li><a href="http://www.isbn.org/standards/home/isbn/transition.asp">ISBN-13
 *       Transition details</a>.</li>
 * </ul>
 */
public final class ISBN10Validator
    extends ModulusValidator<ISBN10> {

    public ISBN10Validator() {
        super(11);
    }

    /**
     * Calculates the <i>weighted</i> value of a charcter in the
     * code at a specified position.
     *
     * <p>For ISBN-10 (from right to left) digits are weighted
     * by their position.</p>
     *
     * {@inheritDoc}
     */
    @Override
    protected int weightedValue( int charValue, int leftPos, int rightPos )
            throws Exception {
        return (charValue * rightPos);
    }

    /**
     * <p>Convert a character at a specified position to an
     * integer value.</p>
     *
     * <p>Character 'X' check digit converted to 10.</p>
     *
     * {@inheritDoc}
     */
    protected int toInt(char character, int leftPos, int rightPos) {
        if (rightPos == 1 && character == 'X') {
            return 10;
        }
        return super.toInt(character, leftPos, rightPos);
    }

}