Question

Here is my Java code:

Scanner userInput = new Scanner(System.in);
while (true) { // forever loop
    try {
        System.out.print("Please type a value: "); // asks user for input
        double n = userInput.nextDouble(); // gets user input as a double
        break; // ends if no error
    }
    catch (Throwable t) { // on error
        System.out.println("NaN"); // not a number
    }
}

You can see what this is supposed to do from the comments.

But when I enter in something that’s not a number, this happens:

Please type a value: abc
NaN
Please type a value: NaN
Please type a value: NaN
Please type a value: NaN
Please type a value: NaN
Please type a value: NaN
Please type a value: NaN

and so on until I force stop it.

In Python I would just do this:

while True:
    try:
        n = float(raw_input("Please type a value: "))
        break
    except Exception:
        print "NaN"

How do I do this in Java?
I’ve tried using a do while.

Answer 1

while (true) { // forever loop
    try {
        scanner userInput = new Scanner(System.in); 
        System.out.print("Please type a value: "); // asks user for input
        double n = userInput.nextDouble(); // gets user input as a double
        break; // ends if no error
    }
    catch (Throwable t) { // on error
        System.out.println("NaN"); // not a number
    }
}

you should use scanner class inside the while loop then only it will ask next input value if the given input value is wrong.