New to Java

The program I am writing is supposed to ask the user to input a 4-digit Integer whose digits are not all the same, and then place the number in descending and ascending order, then subtract until the number 6174 is met.

I'm very new with java but I can't seem to get my if statement to loop back until the condition I want is met.

I know that a while statement will loop back, but when I tried that it just kept looping over and over again.

Any help and tips for later on in my project will be great.

import java.util.Scanner;


public class program2
 {
    public static void main(String[] args)
    {
      int      Number, D1, D2, D3, D4, Temp;
      Scanner  Keyboard = new Scanner(System.in);
      boolean  NoNumberYet;


      System.out.println("Please enter a 4-digit positive integer whose digits are all different: ");
      Number = Keyboard.nextInt();


      D1 = (Number/1000);
      D2 = (Number/100) %10;
      D3 = (Number/10) %10;
      D4 =  Number %10;

      NoNumberYet = true;

      while(NoNumberYet)  
        {
        if (D1 == D2 && D2 == D3 && D3 == D4)
           {
           NoNumberYet = false;
           System.out.println("The number you entered contains the same digits.");
           System.out.print("Please re-enter the number: ");
           Number = Keyboard.nextInt();
           }
        } 



    }