    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 11 <strong>ISBN-10</strong> Check Digit calculation/validation.
    021 * <p>
    022 * ISBN-10 Numbers are a numeric code except for the last (check) digit
    023 * which can have a value of "X".
    024 * <p>
    025 * Check digit calculation is based on <em>modulus 11</em> with digits being weighted
    026 * based by their position, from right to left  with the first digit being weighted
    027 * 1, the second 2 and so on. If the check digit is calculated as "10" it is converted
    028 * to "X".
    029 * <p>
    030 * <strong>N.B.</strong> From 1st January 2007 the book industry will start to use a new 13 digit
    031 * ISBN number (rather than this 10 digit ISBN number) which uses the EAN-13 / UPC
    032 * (see {@link EAN13CheckDigit}) standard.
    033 * <p>
    034 * For further information see:
    035 * <ul>
    036 *   <li><a href="https://en.wikipedia.org/wiki/ISBN">Wikipedia - International
    037 *       Standard Book Number (ISBN)</a>.</li>
    038 *   <li><a href="http://www.isbn.org/standards/home/isbn/transition.asp">ISBN-13
    039 *       Transition details</a>.</li>
    040 * </ul>
    041 *
    042 * @since 1.4
    043 */
    044public final class ISBN10CheckDigit extends ModulusCheckDigit {
    045
    046    private static final long serialVersionUID = 8000855044504864964L;
    047
    048    /** Singleton ISBN-10 Check Digit instance */
    049    public static final CheckDigit ISBN10_CHECK_DIGIT = new ISBN10CheckDigit();
    050
    051    /**
    052     * Constructs a modulus 11 Check Digit routine for ISBN-10.
    053     */
    054    public ISBN10CheckDigit() {
    055        super(MODULUS_11);
    056    }
    057
    058    /**
    059     * <p>Convert an integer value to a character at a specified position.</p>
    060     *
    061     * <p>Value '10' for position 1 (check digit) converted to 'X'.</p>
    062     *
    063     * @param charValue The integer value of the character.
    064     * @return The converted character.
    065     * @throws CheckDigitException if an error occurs.
    066     */
    067    @Override
    068    protected String toCheckDigit(final int charValue)
    069            throws CheckDigitException {
    070        if (charValue == 10) {  // CHECKSTYLE IGNORE MagicNumber
    071            return "X";
    072        }
    073        return super.toCheckDigit(charValue);
    074    }
    075
    076    /**
    077     * <p>Convert a character at a specified position to an
    078     * integer value.</p>
    079     *
    080     * <p>Character 'X' check digit converted to 10.</p>
    081     *
    082     * @param character The character to convert.
    083     * @param leftPos The position of the character in the code, counting from left to right
    084     * @param rightPos The position of the character in the code, counting from right to left
    085     * @return The integer value of the character.
    086     * @throws CheckDigitException if an error occurs.
    087     */
    088    @Override
    089    protected int toInt(final char character, final int leftPos, final int rightPos)
    090            throws CheckDigitException {
    091        if (rightPos == 1 && character == 'X') {
    092            return 10;  // CHECKSTYLE IGNORE MagicNumber
    093        }
    094        return super.toInt(character, leftPos, rightPos);
    095    }
    096
    097    /**
    098     * Calculates the <em>weighted</em> value of a character in the
    099     * code at a specified position.
    100     *
    101     * <p>For ISBN-10 (from right to left) digits are weighted
    102     * by their position.</p>
    103     *
    104     * @param charValue The numeric value of the character.
    105     * @param leftPos The position of the character in the code, counting from left to right
    106     * @param rightPos The position of the character in the code, counting from right to left
    107     * @return The weighted value of the character.
    108     */
    109    @Override
    110    protected int weightedValue(final int charValue, final int leftPos, final int rightPos) {
    111        return charValue * rightPos;
    112    }
    113
    114}