ITEC 120 2009spring ibarland nokie jmdymacek

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lab11a
ISBN-10

Note:this page is yet to be fleshed out...

• We'll go over the following method with the lab-leader:

  class StringLooper { /** Return how many occurrences of `target` occur in `s`. * @param s the string to search through * @param target the char to count. * @return how many occurrences of `target` occur in `s`. */ int countOccurences( String s, char target ) { int seenSoFar = 0; int i=0; while (i < s.length()) { if (s.charAt(i) == target) { seenSoFar = seenSoFar + 1; } // else do nothing. i = i + 1; } return seenSoFar; } }

• Ten-digit book numbers — ISBN-10 — are constructed by taking nine digits of “real” data, and constructing the tenth digit as follows:
  
  That is, compute
  
  Remember, though, that the third digit, x₃, occurs at index 2 of the string. In general, the ith digit x_i is s.charAt(      ).
  For example, for the nine digits "030640615", the tenth digit is
  (1·0+2·3+3·0+4·6+5·4+6·0+7·6+8·1+9·5) mod 11
  = (0 + 6 + 0 + 24 + 20 + 0 + 42 + 8 + 45) mod 11
  = 145 mod 11 = 2, so the check digit is 2. Thus "0306406152" is a valid ISBN-10, but "0306406154" is not.
  (This scheme means that if somebody mis-types a digit, or transposes two adjacent digits, a computer can recognize that an error has been made.)
• Write the following method:

  boolean isValidISBN10( String isbn ) { return false; // stub. }

  From the countOccurences above, we see how to have a loop look at each character individually. One thing we need to do in this problem is to convert a char into an int from 0..9. Here is a helper method you can use, to make your code more readable:

  int charToInt( char digit ) { return Integer.parseInt( Character.toString(digit) ); }

• Here are some tests:

  class StringLooperTester { public static void main( String[] args ) { StringLooper looper = new StringLooper(); System.out.println( "\nTest some okay (but contrived) ISBNs: " ); checkExpect( looper.isValidISBN10("0000000000"), true ); checkExpect( looper.isValidISBN10("1000000001"), true ); checkExpect( looper.isValidISBN10("0100000002"), true ); checkExpect( looper.isValidISBN10("0010000003"), true ); checkExpect( looper.isValidISBN10("0001000004"), true ); checkExpect( looper.isValidISBN10("0000000019"), true ); checkExpect( looper.isValidISBN10("0000000027"), true ); checkExpect( looper.isValidISBN10("2000000010"), true ); checkExpect( looper.isValidISBN10("4000000020"), true ); checkExpect( looper.isValidISBN10("5000000080"), true ); System.out.println( "\nTest some real and incorrect ISBNs: " ); checkExpect( looper.isValidISBN10("0306406152"), true ); checkExpect( looper.isValidISBN10("0306406162"), false ); checkExpect( looper.isValidISBN10("0306406154"), false ); checkExpect( looper.isValidISBN10("0553565699"), true ); checkExpect( looper.isValidISBN10("1553565699"), false ); } static void checkExpect( boolean actual, boolean expected ) { if (actual == expected) { System.out.print("."); } else { System.out.println("failed test: expected " + expected + ", got " + actual ); } } }

• Extra challenge: Actually, sometimes the check-digit works out to be 10. Since that won't fit into a single digit, in that case the letter 'X' is used (reminiscent of the roman numeral).

  Fix your code above so that ISBN-10s ending in the letter 'X' are also recognized.

  System.out.println( "\nTest some X-digit ISBNs: " ); checkExpect( looper.isValidISBN10("000000000X"), false ); checkExpect( looper.isValidISBN10("050000000X"), true ); checkExpect( looper.isValidISBN10("000020000X"), true ); checkExpect( looper.isValidISBN10("300000002X"), true );

• Extra extra challenge: Write char createCheckDigit( String isbnPart )
• Extra extra extra challenge: Can you modify isValidISBN so that it is much much shorter, by having it call createCheckDigit as a helper?
• Extra extra extra extra challenge: Read about ISBN-13, and implement that instead.
  Mkae isValidISBN which can take a 10-digit or a 13-digit input, and return isValidISBN10 or isValidISBN13 as appropriate.

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©2009, Ian Barland, Radford University Last modified 2009.Apr.06 (Mon)

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