Question

I am working on writing a file reader, and the idea is to have the user enter a number that represents the line number from the text file. The variable that holds this number is of type int. However, when the user enters a String instead, Java throws the InputMismatchException exception, and what I want is to have a loop in the catch clause, where I will be looping until the user enters a valid value, i.e. an int. The skeleton looks like this:

 public void _____ throws IOException {
    try {
    // Prompting user for line number
    // Getting number from keyboard
    // Do something with number
    } catch (InputMismatchException e) {
       // I want to loop until the user enters a valid input
       // When the above step is achieved, I am invoking another method here
    }  
}

My question is, what are some possible techniques that could do the validation?
Thank you.

Answer 1

Avoid using exceptions for flow control. Catch the exception, but only print a message. Also, do need for loops within loops.

It’s as simple as this:

public void _____ throws IOException {
    int number = -1;
    while (number == -1) {
        try {
            // Prompt user for line number
            // Getting number from keyboard, which could throw an exception
            number = <get from input>;
        } catch (InputMismatchException e) {
             System.out.println("That is not a number!");
        }  
    }
    // Do something with number
}