// get the difficulty level as a character
// Input: no input, but this method listens to users' keyboard input
// Output: char 'e', 'i', or 'h'
public static char difficulty() {
	char level;

	while(true) {
		System.out.println("Enter your difficulty level:");
		Scanner keyboard = new Scanner(System.in);
		String input = keyboard.nextLine().toLowerCase();

		try {
			if (validation(input) == true) {
				level = getLevel(input);
				return level;
			} else {
				System.out.println("Your input is invalid. "
					."Please re-enter your difficulty level:");
			}
		} catch (NumberFormatException nFE){
			System.out.println("Your input is invalid. "
				."Please re-enter your difficulty level:");
		}
	}
}

// validate the input
// Input: Users' input as a string
// Output: true or false
private static boolean validation(String str) {}