code: public QrCodeEncoder addNumeric(String message) {
  		byte[] numbers = new byte[message.length()];
  
  		for (int i = 0; i < message.length(); i++) {
  			char c = message.charAt(i);
  			int values = c - '0';
  			if (values < 0 || values > 9)
  				throw new RuntimeException("Expected each character to be a number from 0 to 9");
  			numbers[i] = (byte)values;
  		}
  		return addNumeric(numbers);
  	}
docs: Creates a QR-Code which encodes a number sequence
  
  @param message String that specifies numbers and no other types. Each number has to be from 0 to 9 inclusive.
  @return The QR-Code