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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements.  See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache License, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License.  You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   */
17  package org.apache.commons.validator.routines.checkdigit;
18  
19  /**
20   * Modulus 11 <b>ISBN-10</b> Check Digit calculation/validation.
21   * <p>
22   * ISBN-10 Numbers are a numeric code except for the last (check) digit
23   * which can have a value of "X".
24   * <p>
25   * Check digit calculation is based on <i>modulus 11</i> with digits being weighted
26   * based by their position, from right to left  with the first digit being weighted
27   * 1, the second 2 and so on. If the check digit is calculated as "10" it is converted
28   * to "X".
29   * <p>
30   * <b>N.B.</b> From 1st January 2007 the book industry will start to use a new 13 digit
31   * ISBN number (rather than this 10 digit ISBN number) which uses the EAN-13 / UPC
32   * (see {@link EAN13CheckDigit}) standard.
33   * <p>
34   * For further information see:
35   * <ul>
36   *   <li><a href="http://en.wikipedia.org/wiki/ISBN">Wikipedia - International
37   *       Standard Book Number (ISBN)</a>.</li>
38   *   <li><a href="http://www.isbn.org/standards/home/isbn/transition.asp">ISBN-13
39   *       Transition details</a>.</li>
40   * </ul>
41   *
42   * @version $Revision: 1739356 $
43   * @since Validator 1.4
44   */
45  public final class ISBN10CheckDigit extends ModulusCheckDigit {
46  
47      private static final long serialVersionUID = 8000855044504864964L;
48  
49      /** Singleton ISBN-10 Check Digit instance */
50      public static final CheckDigit ISBN10_CHECK_DIGIT = new ISBN10CheckDigit();
51  
52      /**
53       * Construct a modulus 11 Check Digit routine for ISBN-10.
54       */
55      public ISBN10CheckDigit() {
56          super(11);  // CHECKSTYLE IGNORE MagicNumber
57      }
58  
59      /**
60       * Calculates the <i>weighted</i> value of a charcter in the
61       * code at a specified position.
62       *
63       * <p>For ISBN-10 (from right to left) digits are weighted
64       * by their position.</p>
65       *
66       * @param charValue The numeric value of the character.
67       * @param leftPos The position of the character in the code, counting from left to right
68       * @param rightPos The positionof the character in the code, counting from right to left
69       * @return The weighted value of the character.
70       */
71      @Override
72      protected int weightedValue(int charValue, int leftPos, int rightPos) {
73          return charValue * rightPos;
74      }
75  
76      /**
77       * <p>Convert a character at a specified position to an
78       * integer value.</p>
79       *
80       * <p>Character 'X' check digit converted to 10.</p>
81       *
82       * @param character The character to convert.
83       * @param leftPos The position of the character in the code, counting from left to right
84       * @param rightPos The position of the character in the code, counting from right to left
85       * @return The integer value of the character.
86       * @throws CheckDigitException if an error occurs.
87       */
88      @Override
89      protected int toInt(char character, int leftPos, int rightPos)
90              throws CheckDigitException {
91          if (rightPos == 1 && character == 'X') {
92              return 10;  // CHECKSTYLE IGNORE MagicNumber
93          }
94          return super.toInt(character, leftPos, rightPos);
95      }
96  
97      /**
98       * <p>Convert an integer value to a character at a specified position.</p>
99       *
100      * <p>Value '10' for position 1 (check digit) converted to 'X'.</p>
101      *
102      * @param charValue The integer value of the character.
103      * @return The converted character.
104      * @throws CheckDigitException if an error occurs.
105      */
106     @Override
107     protected String toCheckDigit(int charValue)
108             throws CheckDigitException {
109         if (charValue == 10) {  // CHECKSTYLE IGNORE MagicNumber
110             return "X";
111         }
112         return super.toCheckDigit(charValue);
113     }
114 
115 }