public static String HMSFormatConvertor(int callDuration, int minuteUnit) {
        if (callDuration < 0)
            throw new IllegalArgumentException();

        int hours = callDuration / (MinutesPerHour * minuteUnit);
        callDuration = callDuration % (MinutesPerHour * minuteUnit);
        int minutes = (int) (callDuration / minuteUnit);
        int seconds = callDuration % minuteUnit;
        return hours + "小时" + minutes + "分" + seconds + "秒";
    }