PROGRAM 4 : UNIQUE NUMBER

(UNIQUE NUMBER IS A NUMBER IN WHICH NO DIGIT IS REPEATED AND THE FIRST DIGIT IS NOT ZERO (0).
Example: 1234 , 45631 are unique numbers.

11234 , 15675 0987 , are not unique number as one or more digits occur more than once or the first digit is '0' )

PROGRAM:

import java.io.*;
public class unique_number
{
    public static void main(String args[])throws IOException
    {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        System.out.println("Enter a number to find out whether it is an unique number or not:");
        String s = br.readLine();
        int l = s.length() , f = 0;
        for(int i = 0 ; i < l ; i++){
            for(int j = i+1 ; j < l ; j++){
                if(s.charAt(i)==s.charAt(j) || s.charAt(0)=='0'){
                    f++;
                    break;
                }
            }
        }
        if(f==0)
          System.out.println("The number is an unique number.");
        else
          System.out.println("The number is not an unique number.");
        }
    }