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 11 <b>ISBN-10</b> Check Digit calculation/validation.
023     * <p>
024     * ISBN-10 Numbers are a numeric code except for the last (check) digit
025     * which can have a value of "X".
026     * <p>
027     * Check digit calculation is based on <i>modulus 11</i> with digits being weighted
028     * based by their position, from right to left  with the first digit being weighted
029     * 1, the second 2 and so on. If the check digit is calculated as "10" it is converted
030     * to "X".
031     * <p>
032     * <b>N.B.</b> From 1st January 2007 the book industry will start to use a new 13 digit
033     * ISBN number (rather than this 10 digit ISBN number) which uses the EAN-13 / UPC
034     * (see {@link EAN13CheckDigit}) standard.
035     * <p>
036     * For further information see:
037     * <ul>
038     *   <li><a href="http://en.wikipedia.org/wiki/ISBN">Wikipedia - International
039     *       Standard Book Number (ISBN)</a>.</li>
040     *   <li><a href="http://www.isbn.org/standards/home/isbn/transition.asp">ISBN-13
041     *       Transition details</a>.</li>
042     * </ul>
043     *
044     * @version $Revision: 493905 $ $Date: 2007-01-08 03:11:38 +0100 (Mo, 08. Jan 2007) $
045     * @since Validator 1.4
046     */
047    public final class ISBN10CheckDigit extends ModulusCheckDigit implements Serializable {
048    
049        /** Singleton ISBN-10 Check Digit instance */
050        public static final CheckDigit INSTANCE = new ISBN10CheckDigit();
051    
052        /**
053         * Construct a modulus 11 Check Digit routine for ISBN-10.
054         */
055        public ISBN10CheckDigit() {
056            super(11);
057        }
058    
059        /**
060         * Calculates the <i>weighted</i> value of a charcter in the
061         * code at a specified position.
062         *
063         * <p>For ISBN-10 (from right to left) digits are weighted
064         * by their position.</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 positionof the character in the code, counting from right to left
069         * @return The weighted value of the character.
070         */
071        protected int weightedValue(int charValue, int leftPos, int rightPos) {
072            return (charValue * rightPos);
073        }
074    
075        /**
076         * <p>Convert a character at a specified position to an
077         * integer value.</p>
078         *
079         * <p>Character 'X' check digit converted to 10.</p>
080         *
081         * @param character The character to convert.
082         * @param leftPos The position of the character in the code, counting from left to right 
083         * @param rightPos The positionof the character in the code, counting from right to left
084         * @return The integer value of the character.
085         * @throws CheckDigitException if an error occurs.
086         */
087        protected int toInt(char character, int leftPos, int rightPos)
088                throws CheckDigitException {
089            if (rightPos == 1 && character == 'X') {
090                return 10;
091            } else {
092                return super.toInt(character, leftPos, rightPos);
093            }
094        }
095    
096        /**
097         * <p>Convert an integer value to a character at a specified position.</p>
098         *
099         * <p>Value '10' for position 1 (check digit) converted to 'X'.</p>
100         *
101         * @param charValue The integer value of the character.
102         * @return The converted character.
103         * @throws CheckDigitException if an error occurs.
104         */
105        protected String toCheckDigit(int charValue)
106                throws CheckDigitException {
107            if (charValue == 10) {
108                return "X";
109            } else {
110                return super.toCheckDigit(charValue);
111            }
112        }
113    
114    }