Java try-catch input validation with do-while loop

Question

I've been sitting here (embarrassingly) for hours trying to get a do-while loop to to accept user input until it's valid, but I seem to be messing up when it comes to the boolean that I'm using to try and exit the loop. Whenever I can get the program to partially work the catch exception just ends up repeating itself infinitely.

Scanner scnr = new Scanner(System.in);

double wallHeight = 0.0;
boolean valid = false;

// Implement a do-while loop to ensure input is valid
// Prompt user to input wall's height
do {
    try {
        System.out.println("Enter wall height (feet): ");
        wallHeight = scnr.nextDouble();
        valid = false;

        if (wallHeight <=0) {
            throw new Exception ("Invalid Input");
        }
    }
    catch (Exception e) {
        System.out.println("Invalid Input");
    }
} while (!valid);

Answer 1

Start by assuming the input is valid (and set valid to true on every iteration of the loop). Only set valid to false when you encounter an exception (hopefully the one you raised).

do {
    valid = true;
    try {
        System.out.println("Enter wall height (feet): ");
        wallHeight = scnr.nextDouble();
        if (wallHeight <= 0) {
            throw new Exception("Invalid Input");
        }
    } catch (Exception e) {
        valid = false;
        System.out.println("Invalid Input");
    }
} while (!valid);

Note that you do not appear to need an exception here, as

do {
    valid = true;
    System.out.println("Enter wall height (feet): ");
    wallHeight = scnr.nextDouble();
    if (wallHeight <= 0) {
        System.out.println("Invalid Input");
        valid = false;
    }
} while (!valid);

would also work. Of course, that assumes the user only inputs valid double (s). If you need handle arbitrary input, you should check that there is a double before you attempt to consume it (and you must consume anything that isn't a double or you have an infinite loop). Like,

do {
    valid = true;
    System.out.println("Enter wall height (feet): ");
    if (scnr.hasNextDouble()) {
        wallHeight = scnr.nextDouble();
        if (wallHeight <= 0) {
            System.out.println("Invalid Input");
            valid = false;
        }
    } else {
        System.out.println("Invalid Input " + scnr.nextLine());
        valid = false;
    }
} while (!valid);

Answer 2

Here is another take.I just moved the code that sets valid = true after the if check. It can make it that far only when its valid. Otherwise valid will be false and it will loop.

public class BasicDoWhile {

    public static void main(String[] args) {
        double wallHeight = 0.0;
        boolean valid = false;

        Scanner scnr = new Scanner(System.in);

        // Implement a do-while loop to ensure input is valid
        // Prompt user to input wall's height
        do {
            try {
                System.out.println("Enter wall height (feet): ");
                wallHeight = scnr.nextDouble();

                if (wallHeight <= 0) {
                    throw new Exception("Invalid Input");
                }

                valid = true;

            }
            catch (Exception e) {
                System.out.println("Invalid Input");
            }

        } while (!valid);

    }
}