main method and two static methods and loop until input zero

Can somebody please tell me what I've done wrong and how to fix it? I'm ready to bash my skull!

This is the problem:
Write a class with a main() method and two static methods. Your program should prompt the user for a single-digit integer. Your program should print out to the screen the integer written out as a word. This should loop until the user enters the integer 0

This is my code:

i can't find any problem with your code !! it looks nice.

Your code is fine.. except..below thing..
converttoString(digit); // here you are passing number which is not initialzed... so default values is 0
System.out.println("Your number " + digit + " in words is " + numString);// here u need to print numString.
after making above changes it works fine.. atleast for me..

package src;

import java.util.Scanner;

public class Exa {


static String numberString = null;
// Main method
public static void main(String[] args) {


Exa ex=new Exa();
// Create a scanner
Scanner input = new Scanner(System.in);

// Prompt the user to enter a single digit integer
System.out.println("Enter a single digit integer" + "Enter 0 to exit");
System.out.print("Integer?");
int digit = input.nextInt();




while (digit >= 0) {
// Sentinal statement to exit loop
if (digit == 0) {
System.out.print( "Thank you for playing! " + "Good bye! ");
break; }
// Continue into loop
else if (digit != 0)
// Call public static boolean validateLength(digit) method to validate integer is only one digit
if(validateLength(digit) == true){
// Call public static String convertIntegerToWords(number) method to convert integer "digit" to word form
ex.convertIntegerToWords(digit);
// Output the word value for the integer entered
System.out.println ("Your number " + digit + " in words is " + numberString );
// Prompt user to enter another integer or press 0 to quit
// Ensures loop will be finite
System.out.print("Enter a number or press 0 to quit.");
digit = input.nextInt();
}
System.out.print("Enter a number or press 0 to quit.");
digit = input.nextInt();
}
}
// Method to validate length of integer
public static boolean validateLength(int digit) {

// Validate length of integer
if ((digit > 0) && (digit < 10))
return true;

else
System.out.println("The integer is too long");
return false;
}
// Method to convert integer into words using a switch statement
public String convertIntegerToWords(int digit) {

switch (digit) {
case 1: numberString = "one";
break;
case 2: numberString = "two";
break;
case 3: numberString = "three";
break;
case 4: numberString = "four";
break;
case 5: numberString = "five";
break;
case 6: numberString = "six";
break;
case 7: numberString = "seven";
break;
case 8: numberString = "eight";
break;
case 9: numberString = "nine";
break;
}
return numberString;
}
}