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;
}
}