Homework 4 - ISBN Checker

(Credit to John Motil, SIGCSE Nifty Assignments 2006.)

The International Standard Book Number (ISBN) is a unique identifier for books. The old standard, ISBN-10, calls for 10 digits, laid out as follows (from wikipedia):

The group identifier (language)
The publisher code
The item number (title)
A checksum or check digit

The check digit is calculated from the previous digits of the ISBN and is used as a form of error detection. For example, if a digit is mistyped (e.g., by a distributor trying to specify which book they want 10,000 copies of), the check digit catches that error. This is a simple version of an error detection code which are common in computer science. They are used in a variety of applications to ensure that a piece of data has not been corrupted, e.g., packets over the Internet, hard disk drives, and computer memory.

The check digit is calculated by first summing the first digit plus two times the second digit plus third times the third all the way to nine times the ninth digit. The remainder of this sum when divided by 11 is then computed. If the remainder is 10, then the check symbol is "X". Otherwise, the check symbol is the remainder. That is, the calculation is

For example, consider the number 0205080057. This calculation on the first nine digits yields 7 which is the 10th (check) digit of the number. Thus the number is a valid ISBN.

The new standard, ISBN-13 is similar to a ISBN-10 except that the first three digits designate the industry under which this product belongs. In the case of books, these first three digits will always be 978.

However, because the format of the code is different, the calculation of the check digit must also change. To the calculate the check digit of an ISBN-13 code, you sum the first 12 digits of the code like with ISBN-10. However, in addition to summation, you also alternate multiplying each digit by 1 or 3, from left to right, during the summation process. The result is taken modulo 10, giving a value from 0 to 9 and that value is subtracted from 10, giving a final result in the range 1 to 10. The check digit is 0 if the final result is 10. Otherwise it is simply the final result itself. To summarize, the calculation for ISBN-13 codes is

Your task is to write a program, ISBNChecker, that will prompt the user to the type of ISBN code they wish to check, the code itself, and then report if that code is valid. Your program should be in a class called ISBNChecker in a file called ISBNChecker.java.

Output

Here are several executions of the program highlighting the different cases that can occur. Input from the user is both bolded and underlined.

Sample execution #1:

This program checks to see if a given ISBN is valid.
It can process both ISBN-10 and ISBN-13 codes.

What kind of ISBN do you want to check? [ISBN-10, ISBN-13]: ISBN-10
Enter the ISBN-10 code to check: 0136091814
0136091814 is a valid ISBN-10 code.

Sample execution #2:

This program checks to see if a given ISBN is valid.
It can process both ISBN-10 and ISBN-13 codes.

What kind of ISBN do you want to check? [ISBN-10, ISBN-13]: ISBN-10
Enter the ISBN-10 code to check: 0136091812
0136091812 is not a valid ISBN-10 code.
Expected 4, but found 2.

Sample execution #3:

This program checks to see if a given ISBN is valid.
It can process both ISBN-10 and ISBN-13 codes.

What kind of ISBN do you want to check? [ISBN-10, ISBN-13]: ISBN-13
Enter the ISBN-13 code to check: 9780136091813
9780136091813 is a valid ISBN-13 code.

Sample execution #4:

This program checks to see if a given ISBN is valid.
It can process both ISBN-10 and ISBN-13 codes.

What kind of ISBN do you want to check? [ISBN-10, ISBN-13]: ISBN-13
Enter the ISBN-13 code to check: 9780136091817
9780136091817 is not a valid ISBN-13 code.
Expected 3, but found 7.

Sample execution #5:

This program checks to see if a given ISBN is valid.
It can process both ISBN-10 and ISBN-13 codes.

What kind of ISBN do you want to check? [ISBN-10, ISBN-13]: Cake
Cake is an invalid ISBN type.

Sample execution #6:

This program checks to see if a given ISBN is valid.
It can process both ISBN-10 and ISBN-13 codes.

What kind of ISBN do you want to check? [ISBN-10, ISBN-13]: ISBN-10
Enter the ISBN-10 code to check: 123456789X
123456789X is a valid ISBN-10 code.

(The above ISBN codes are from our textbook.)

As you can tell from the above examples, the program produces a preamble that describes what the program does and then prompts the user for type of ISBN to check and then the code. The program then computes the check and then reports back to the user is the expected check digit matches the actual check digit.

Your solution must reproduce the above output exactly. In particular, format, capitalization, punctuation, and spacing should all be preserved. Note when a user input is echoed in the output, e.g., "ISBN-13" and "Cake" in execution #5.

When the user enters in the type of ISBN they want to check, they may enter either "ISBN-10" or "ISBN-13". Your program should check for these strings exactly, i.e., "isbn-10", "iSbn-13", and "ISBn-10" are all examples of invalid types. When an invalid type is given, the program prints the above error message and exits without computing anything.

In contrast, you can assume that the code given by the user is a string of digits of the appropriate length. You do not need to check the length of the input to ensure that it is valid or individual characters to ensure that they are digits.

Design

Unlike previous homeworks, there is no visual pattern for you to decompose. However, the principles of decomposition still apply! You should have at least 3 static methods that perform useful functionality and decompose the problem of computing ISBNs in a meaningful way. As a first step, you should look at the example runs above and split up the output based on functionality. That division should suggest a beginning set of methods to write. There is certainly room for more opportunities to decompose the problem further, so keep an eye out for them!

Throughout this homework, you will need to convert from chars to ints and vice versa. As we discussed in class, you must be wary because a char can automatically converted into an int, but the resulting value is the character code of the char rather than the numeric value of the char if it happens to be a digit. This frequently results in confusion because this is an error not caught by the compiler and (in Java, at least) can only be caught via testing. Chapter 4.3 of the text explains these pitfalls and how to avoid them in more detail.

Testing

Even though we give you a few sample executions for you to mimic, their success does not guarantee that your program will run correctly! When we test your program, we will try out other ISBNs to make sure that your program works in a variety of cases.

Therefore, you should try out your program on other books that you own to gain confidence that it indeed works on all inputs. Books published before 2007 will only have an ISBN-10 code, whereas post-2007 books typically feature both an ISBN-10 and ISBN-13 code on the back.

Note that, in rare cases, ISBN codes may be entered incorrectly by the publisher from the beginning which results in invalid ISBNs on books. In the off-chance that your book's ISBN does not validate and you're sure that you've done everything right, try another book.

Submission

Please submit your Java source file, ISBNChecker.java, electronically via the course website.