Using while loop as input validation

Question

I'm trying to use while loop to ask the user to reenter if the input is not an integer

for eg. input being any float or string

      int input;

      Scanner scan = new Scanner (System.in);

      System.out.print ("Enter the number of miles: ");
      input = scan.nextInt();
      while (input == int)  // This is where the problem is
          {
          System.out.print("Invalid input. Please reenter: ");
          input = scan.nextInt();
          }

I can't think of a way to do this. I've just been introduced to java

Take a look at the `Scanner.hasNext` methods. There you can determine which type the next input is. — Simon Forsberg, Sep 19 '13 at 23:06

score 1 · Answer 1 · answered Sep 19 '13 at 23:10

The issue here is that scan.nextInt() will actually throw an InputMismatchException if the input cannot be parsed as an int.

Consider this as an alternative:

    Scanner scan = new Scanner(System.in);

    System.out.print("Enter the number of miles: ");

    int input;
    while (true) {
        try {
            input = scan.nextInt();
            break;
        }
        catch (InputMismatchException e) {
            System.out.print("Invalid input. Please reenter: ");
            scan.nextLine();
        }
    }

    System.out.println("you entered: " + input);

score 1 · Answer 2 · answered Sep 19 '13 at 23:10

1

The javadocs say that the method throws a InputMismatchException if the input doesn;t match the Integer regex. Perhaps this is what you need?

So...

int input = -1;
while(input < 0) {
  try {
     input = scan.nextInt();
  } catch(InputMismatchException e) {
    System.out.print("Invalid input. Please reenter: ");
  }
}

as an example.

answered Sep 19 '13 at 23:10

Aaron

652
4
10

Except -1 is probably a valid number as far as you're concerned. The answer below mine would work. – Aaron Sep 19 '13 at 23:13
FYI: "below" quickly loses its meaning based on edits and a users setting as seen in the tab (i.e., oldest, ...). – ChiefTwoPencils Sep 19 '13 at 23:36

Using while loop as input validation

2 Answers2