private void setEmpLetter (char e) {
        for(int i = 0; i<nonEmpNumbers.length; i++) {
            if(nonEmpNumbers[i] == e) {
                String input = JOptionPane.showInputDialog(null, "Not a valid letter. Enter a letter between A-M.");
                input.charAt(0);
            }

            empLetter = e;
        }
    }