Handle StringIndexOutOfBoundsException for string

Question

try {
    string = scan.nextLine().charAt(0);
} catch(StringIndexOutOfBoundsException siobe){
    System.out.println("invalid input");
}

I am trying to use this code for handling exception for the string that i am getting from a text file. But i get an error saying try to change the actual string declaration to character. I am not sure how to handle this ?

Answer 1

But i get an error saying try to change the actual string declaration to character.

scan.nextLine().charAt(0) is a char so if string is a String (as implied by the compilation error you got), you can't assign a char to it.

If you need just the first character of the input line, you should store it in a char variable.

char first;
try {
    first = scan.nextLine().charAt(0);
} catch(StringIndexOutOfBoundsException siobe){
    System.out.println("invalid input");
}

Of course you can avoid the need to catch this exception if you test the length of the String before getting its first character :

char first;
String line = scan.nextLine();
if (line.length() > 0)
    first = line.charAt(0);
else
    System.out.println("invalid input");

Answer 2

Your compilation error is because String.charAt() returns a char, not a String. They're different types - and you need to be very clear about the difference between them. You could just change the variable to a char variable, renaming it at the same time - but that's a really bad way of checking whether or not a string is empty. Deliberately provoking an exception like this when you can just test it directly is a bad idea - any time you find yourself catching a specific RuntimeException, you should ask yourself whether there's a better way of avoiding it.

You should use String.isEmpty() or String.length() before trying to take the first character of it. For example:

String line = scan.nextLine();
if (line.isEmpty()) { // Or line.length() == 0
    // Whatever you want to do for invalid input.
} else {
    char firstChar = line.charAt(0);
    // Use firstChar
}

Of course, if you don't actually need the first character, and you were just trying to detect empty strings, you can just use the first part of this, without the else.