Question

I’ve run into the following problem with my program (only on attempting to run it, builds fine):

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: 
String index out of range: 57
at java.lang.String.substring(String.java:1907)
at Question7.main(Question7.java:68)

I know there are similar questions on the site, but I’m going through the steps in my head and can’t figure out where this is going wrong.
I don’t think the context of the code/question asked is very important; I believe the problem has something to do with the following lines:

else if (s1.substring(i,i+1).matches("[0-9]"))

if (counthyphen == 3 && countdigits == 9 && (s1.substring(i, i+1).matches("[0-9]") || s1.substring(i, i+1).matches("X")))

But please, have a look for yourself. Help would be much appreciated!

public class Question7
{
public static void main(String args[])
{
    //Declare and initialize.
    String s1 = new String("0-471-34609-8");
    int counthyphen = 0, countdigits = 0;

    //Begin "for" loop.
    for (int i = 0; i < s1.length()-1; i++)
    {
        /////////////////////////////////
        // Check for missing hyphens //
        if (s1.charAt(1) != '-')
        {
            i = s1.length();
        }
        else if (s1.charAt(11) != '-')
        {
            i = s1.length();
        }

        // Now add to the count values //
        if (s1.charAt(i) == '-')
        {
            counthyphen++;
        }
        **else if (s1.substring(i,i+1).matches("[0-9]"))**
        {
            countdigits++;
        }
        /////////////////////////////////
    }

    int i = s1.charAt(s1.length()-1);
    //Check if it's an ISBN and print result.
    **if (counthyphen == 3 && countdigits == 9 && (s1.substring(i, i+1).matches("[0-9]") || s1.substring(i, i+1).matches("X")))**
    {
        System.out.print("This number is an ISBN.");
    }
    else
    {
        System.out.print("This number is NOT an ISBN.");
    }
}
}

Answer 1

int i = s1.charAt(s1.length()-1);

This code stores the ASCII code of the character at the index : – s1.length() - 1, that can certainly be greater than the maximum accessible string index.

For e.g, the last character in your current string is 8, whose ASCII code is: – 56, and that would certainly fail.

So, s1.substring(i, i+1) in your if condition after that would fail.

In fact, I don’t understand the need of that line at all. Why are you using it?

---

Also, your if-else block seems buggy to me: –

    if (s1.charAt(1) != '-')
    {
        i = s1.length();
    }
    else if (s1.charAt(11) != '-')
    {
        i = s1.length();
    }

Why have you assigned same value to i in both the blocks there?

May be you wanted something like this: –

    if (s1.charAt(1) != '-' || s1.charAt(11) != '-')
    {
        break;  // Just break if not a valid string
    }