private static String convertOneDigit(final char digit) {

        switch (digit) {
            case '1' : return "one";
            case '2' : return "two";
            case '3' : return "three";
            case '4' : return "four";
            case '5' : return "five";
            case '6' : return "six";
            case '7' : return "seven";
            case '8' : return "eight";
            case '9' : return "nine";
            default : return "";
        }
    }