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 * https://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
18 package org.apache.commons.validator.routines.checkdigit;
19
20 /**
21 * Modulus 11 <strong>ISBN-10</strong> Check Digit calculation/validation.
22 * <p>
23 * ISBN-10 Numbers are a numeric code except for the last (check) digit which can have a value of "X".
24 * </p>
25 * <p>
26 * Check digit calculation is based on <em>modulus 11</em> with digits being weighted based by their position, from right to left with the first digit being
27 * weighted 1, the second 2 and so on. If the check digit is calculated as "10" it is converted to "X".
28 * </p>
29 * <p>
30 * <strong>N.B.</strong> 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
31 * the EAN-13 / UPC (see {@link EAN13CheckDigit}) standard.
32 * </p>
33 * <p>
34 * For further information see:
35 * </p>
36 * <ul>
37 * <li><a href="https://en.wikipedia.org/wiki/ISBN">Wikipedia - International Standard Book Number (ISBN)</a>.</li>
38 * <li><a href="https://www.isbn.org/standards/home/isbn/transition.asp">ISBN-13 Transition details</a>.</li>
39 * </ul>
40 *
41 * @since 1.4
42 */
43 public final class ISBN10CheckDigit extends ModulusCheckDigit {
44
45 private static final long serialVersionUID = 8000855044504864964L;
46
47 /**
48 * Singleton ISBN-10 Check Digit instance.
49 */
50 public static final CheckDigit ISBN10_CHECK_DIGIT = new ISBN10CheckDigit();
51
52 /** An ISBN-10 is exactly ten characters, the last being the check digit. */
53 private static final int ISBN10_LEN = 10;
54
55 /**
56 * Constructs a modulus 11 Check Digit routine for ISBN-10.
57 */
58 public ISBN10CheckDigit() {
59 super(MODULUS_11);
60 }
61
62 /**
63 * {@inheritDoc}
64 *
65 * <p>
66 * The weight is {@code rightPos}, which does not change when a character is prepended, and modulus 11 makes the
67 * leading position weight a multiple of the modulus, so {@code ModulusCheckDigit} would accept an over-length code
68 * with any prepended digit (for example {@code 51930110995}). The ten-character length is checked here before the
69 * check digit test.
70 * </p>
71 */
72 @Override
73 public boolean isValid(final String code) {
74 return isLength(code, ISBN10_LEN) && super.isValid(code);
75 }
76
77 /**
78 * Convert an integer value to a character at a specified position.
79 * <p>
80 * Value '10' for position 1 (check digit) converted to 'X'.
81 * </p>
82 *
83 * @param charValue The integer value of the character.
84 * @return The converted character.
85 * @throws CheckDigitException if an error occurs.
86 */
87 @Override
88 protected String toCheckDigit(final int charValue) throws CheckDigitException {
89 if (charValue == 10) { // CHECKSTYLE IGNORE MagicNumber
90 return "X";
91 }
92 return super.toCheckDigit(charValue);
93 }
94
95 /**
96 * Convert a character at a specified position to an integer value.
97 * <p>
98 * Character 'X' check digit converted to 10.
99 * </p>
100 *
101 * @param character The character to convert.
102 * @param leftPos The position of the character in the code, counting from left to right.
103 * @param rightPos The position of the character in the code, counting from right to left.
104 * @return The integer value of the character.
105 * @throws CheckDigitException if an error occurs.
106 */
107 @Override
108 protected int toInt(final char character, final int leftPos, final int rightPos) throws CheckDigitException {
109 if (rightPos == 1 && character == 'X') {
110 return 10; // CHECKSTYLE IGNORE MagicNumber
111 }
112 return super.toInt(character, leftPos, rightPos);
113 }
114
115 /**
116 * Calculates the <em>weighted</em> value of a character in the code at a specified position.
117 *
118 * <p>
119 * For ISBN-10 (from right to left) digits are weighted by their position.
120 * </p>
121 *
122 * @param charValue The numeric value of the character.
123 * @param leftPos The position of the character in the code, counting from left to right.
124 * @param rightPos The position of the character in the code, counting from right to left.
125 * @return The weighted value of the character.
126 */
127 @Override
128 protected int weightedValue(final int charValue, final int leftPos, final int rightPos) {
129 return charValue * rightPos;
130 }
131 }