Created
January 31, 2015 09:13
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package isbn; | |
import java.util.regex.Pattern; | |
/** | |
* ISBN class. | |
*/ | |
public class Isbn { | |
/** Number of digits in ISBN. */ | |
public static final int LENGTH = 13; | |
/** Number of digits in old ISBN. */ | |
public static final int OLD_LENGTH = 10; | |
/** | |
* Check whether the number sequence is valid as ISBN. | |
* Check method is: http://en.wikipedia.org/wiki/International_Standard_Book_Number#Check_digits | |
* @param numberSequence the number sequence which you want to check. This sequence is allowed to include hyphens | |
* @return true if the number sequence is valid as ISBN, otherwise false | |
*/ | |
public static boolean isValid(String numberSequence) { | |
if (numberSequence == null) throw new NullPointerException(); | |
if (!Pattern.matches("^\\d+(-?\\d+)*$", numberSequence)) return false; | |
String normalizedSequence = removeHyphen(numberSequence); | |
if (normalizedSequence.length() == 13) return isValidAsIsbn13(normalizedSequence); | |
else if (normalizedSequence.length() == 10) return isValidAsIsbn10(normalizedSequence); | |
else return false; | |
} | |
/** | |
* Check whether the 13-digits number is valid as 13-digits ISBN. | |
* @param number 13-digits number which you want to check. This must not include hyphens | |
* @return true if the 13-digits number is valid as ISBN, otherwise false | |
* @throws IllegalArgumentException number is not 13-digits | |
*/ | |
static boolean isValidAsIsbn13(String number) { | |
if (number == null) throw new NullPointerException(); | |
if (!Pattern.matches("^\\d{" + LENGTH + "}$", number)) throw new IllegalArgumentException(); | |
char[] digits = number.toCharArray(); | |
final int myDigit = computeIsbn13CheckDigit(digits); | |
int checkDigit = digits[LENGTH - 1] - '0'; | |
return myDigit == 10 && checkDigit == 0 || myDigit == checkDigit; | |
} | |
/** | |
* Compute the check digits of 13-digits ISBN. | |
* Both full 13-digits and check-digit-less 12-digits are allowed as the argument. | |
* @param digits the array of each digit in ISBN. | |
* @return check digit | |
* @throws IllegalArgumentException the length of the argument array is neither 12 nor 13 or the element of digits is negative | |
*/ | |
static int computeIsbn13CheckDigit(char[] digits) { | |
if (digits == null) throw new NullPointerException(); | |
if (digits.length != LENGTH && digits.length != LENGTH - 1) throw new IllegalArgumentException(); | |
for (char c : digits) { | |
if (c < '0' || '9' < c) throw new IllegalArgumentException(); | |
} | |
int[] weights = {1, 3}; | |
int sum = 0; | |
for (int i = 0; i < LENGTH - 1; ++i) { | |
sum += (digits[i] - '0') * weights[i % 2]; | |
} | |
return 10 - sum % 10; | |
} | |
/** | |
* Check whether the 10-digits number is valid as 10-digits ISBN. | |
* @param number 10-digits number which you want to check. This must not include hyphens | |
* @return true if the 10-digits number is valid as ISBN, otherwise false | |
* @throws IllegalArgumentException number is not 10-digits | |
*/ | |
static boolean isValidAsIsbn10(String number) { | |
if (number == null) throw new NullPointerException(); | |
if (!Pattern.matches("^\\d{" + OLD_LENGTH + "}$", number)) throw new IllegalArgumentException(); | |
char[] digits = number.toCharArray(); | |
final int myDigit = computeIsbn10CheckDigit(digits); | |
if (myDigit == 10) return digits[9] == 'X'; | |
final int checkDigit = digits[9] - '0'; | |
return myDigit == 11 && checkDigit == 0 || myDigit == checkDigit; | |
} | |
/** | |
* Compute the check digits of 10-digits ISBN. | |
* Both full 10-digits and check-digit-less 9-digits are allowed as the argument. | |
* @param digits the array of each digit in ISBN. | |
* @return check digit | |
* @throws IllegalArgumentException the length of the argument array is neither 9 nor 10 / the element in digits is negative | |
*/ | |
static int computeIsbn10CheckDigit(char[] digits) { | |
if (digits == null) throw new NullPointerException(); | |
if (digits.length != OLD_LENGTH && digits.length != OLD_LENGTH - 1) throw new IllegalArgumentException(); | |
for (char c : digits) { | |
if (c < '0' || '9' < c) throw new IllegalArgumentException(); | |
} | |
int sum = 0; | |
for (int i = 0, weight = 10; i < 9; ++i, --weight) { | |
sum += (digits[i] - '0') * weight; | |
} | |
return 11 - sum % 11; | |
} | |
/** | |
* Convert 10-digits ISBN to 13-digits ISBN. Check digit is re-computed. | |
* @param isbn10 10-digits ISBN. It can include hyphens | |
* @return 13-digits ISBN | |
* @throws IllegalArgumentException the number of digits of the argument is not 10 | |
*/ | |
public static String toIsbn13(String isbn10) { | |
if (isbn10 == null) throw new NullPointerException(); | |
String normalizedNumber = removeHyphen(isbn10); | |
if (normalizedNumber.length() != OLD_LENGTH) throw new IllegalArgumentException(); | |
// Compute check digit | |
String isbn13 = "978" + normalizedNumber.substring(0, OLD_LENGTH - 1); | |
final int checkDigit = computeIsbn13CheckDigit(isbn13.toCharArray()); | |
// Compose 13-digits ISBN from 10-digits ISBN | |
if (isbn10.contains("-")) { | |
return "978-" + isbn10.substring(0, isbn10.length() - 2) + "-" + String.valueOf(checkDigit); | |
} else { | |
return "978" + isbn10.substring(0, isbn10.length() - 1) + String.valueOf(checkDigit); | |
} | |
} | |
/** | |
* Remove hyphens in the argument string. | |
* @param s | |
* @return string where hyphens are removed | |
*/ | |
static String removeHyphen(String s) { | |
if (s == null) throw new NullPointerException(); | |
return s.replace("-", ""); | |
} | |
/** | |
* Static factory. | |
* @param number ISBN which you want to instantiate. | |
* @return ISBN Object | |
* @throws IllegalArgumentException if the argument is invalid as ISBN | |
*/ | |
public static Isbn of(String number) throws IllegalArgumentException { | |
if (number == null) throw new NullPointerException(); | |
if (!isValid(number)) throw new IllegalArgumentException(); | |
if (removeHyphen(number).length() == OLD_LENGTH) { | |
return new Isbn(toIsbn13(number)); | |
} else { | |
return new Isbn(number); | |
} | |
} | |
private final String originalIsbn; | |
private final String normalizedIsbn; // hyphens are removed | |
private final String prefix; | |
private final String group; | |
private final String publisher; | |
private final String bookName; | |
private final String checkDigit; | |
private Isbn(String originalIsbn) { | |
assert null != originalIsbn; | |
this.originalIsbn = originalIsbn; | |
this.normalizedIsbn = removeHyphen(this.originalIsbn); | |
String[] numbers = this.originalIsbn.split("-"); | |
if (numbers.length == 5) { | |
this.prefix = numbers[0]; | |
this.group = numbers[1]; | |
this.publisher = numbers[2]; | |
this.bookName = numbers[3]; | |
this.checkDigit = numbers[4]; | |
} else { | |
this.prefix = ""; | |
this.group = ""; | |
this.publisher = ""; | |
this.bookName = ""; | |
this.checkDigit = ""; | |
} | |
} | |
public String getIsbn() { | |
return originalIsbn; | |
} | |
public String getPrefix() { | |
return prefix; | |
} | |
public String getGroup() { | |
return group; | |
} | |
public String getPublisher() { | |
return publisher; | |
} | |
public String getBookName() { | |
return bookName; | |
} | |
public String getCheckDigit() { | |
return checkDigit; | |
} | |
/** | |
* @return original description of ISBN. It can include hyphens like 978-4-***-*****-*. | |
*/ | |
@Override | |
public String toString() { | |
return originalIsbn; | |
} | |
@Override | |
public boolean equals(Object obj) { | |
if (this == obj) | |
return true; | |
if (!(obj instanceof Isbn)) | |
return false; | |
Isbn other = (Isbn)obj; | |
return other.normalizedIsbn.equals(normalizedIsbn); | |
} | |
@Override | |
public int hashCode() { | |
final int prime = 31; | |
int result = 1; | |
result = prime * result + normalizedIsbn.hashCode(); | |
return result; | |
} | |
} |
Bug is on line 65. If the checksum is 10, you should return 0. For example:
int modulo = sum % 10;
return modulo == 0 ? 0 : 10 - modulo;
Same error is on line 103 for ISBN 10 check digits. Another way to account for this is just run modulo again. For example: return (11 - sum % 11) % 11;
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Doesn't work. Generates a 14 character ISBN13s: