java - Scanner Exception Retry

Question

How to make scanner retry when exception occur?
Consider this app running on CLI mode.

Example:

System.out.print("Define width: ");
    try {
        width = scanner.nextDouble();
    } catch (Exception e) {
        System.err.println("That's not a number!");
        //width = scanner.nextDouble(); // Wrong code, this bring error.
    }

If the user not inputting double type input, then the error thrown. But i want after the error message appears. It's should be asking the user input the width again.

How to do that?

Answer 1

If I understood you correctly, you want the program to ask the user to re-enter a right input after it fails. In that case you can do something like:

boolean inputOk = false;
while (!inputOk) {
    System.out.print("Define width: ");
    try {
        width = scanner.nextDouble();
        inputOk = true;
    } catch (InputMismatchException e) {
        System.err.println("That's not a number!");
        scanner.nextLine();   // This discards input up to the 
                              // end of line
        // Alternative for Java 1.6 and later
        // scanner.reset();   
    }
}

Note: you should only catch and retry for a InputMismatchException. The nextXxx methods throw other exceptions, and if you attempt to retry those, your application will go into an infinite loop.