How To Check To See If Input Is Numerical

My program here asks for an unit to choose from (fl.oz, gal, oz, lb, in, ft, or mi), asks how much of it they have, and asks for the unit they wish to convert to (mL, l, g, kg, mm, cm, m, or km).

My program works, refusing to convert from silly conversions such as gal to cm, telling you to re-input if they enter anything other than fl.oz, gal, etc.

The only thing I cannot figure out is if the user inputs something like "foo" when the program prompts the user for how much of the unit they have. My goal is to have the program say something like "That is not a number! Please enter a numerical value."

My current dilemma right now is that if the user inputs something other than a number, it will catch the exception and print a line telling the user it's not a number, except, it does it infinitely (stuck in a loop). Here is my code:

import java.util.InputMismatchException;
import java.util.Scanner;
public class UnitConversions {
public static void main(String[] args) {
Scanner s = new Scanner(System.in);
double result = 0;

[Code] ....