code: public static synchronized String generateKey() {
  		String code = "";
  
  		long nr = System.currentTimeMillis();
  		if (nr <= lastnr) {
  			nr = lastnr + 1;
  		}
  		lastnr = nr;
  		String s = String.valueOf(nr);
  		for (int i = 0; i < s.length(); i++) {
  			code += codeArray[randomizer.nextInt(6)][s.charAt(i) - 48];
  		}
  		return code;
  	}
docs: Generates a random key which is guaranteed to be unique within the application.
  
  @return