//calculateTotalHours()
public static String calculateTotalHours(Cell inTime, Cell outTime, Cell breakStart, Cell breakEnd)
{
    System.out.println(LOG + "calculateTotalHours");
    SimpleDateFormat timeFormat = new SimpleDateFormat("HH:mm");
    Date in, out, start, end;

    if(null != inTime && null != outTime && null != breakStart && null != breakEnd)
    {
        try
        {
            in = timeFormat.parse(inTime.getStringCellValue());
            out = timeFormat.parse(outTime.getStringCellValue());
            start = timeFormat.parse(breakStart.getStringCellValue());
            end = timeFormat.parse(breakEnd.getStringCellValue());

            long lunchTotal = end.getTime() - start.getTime();
            long totalWork = out.getTime() - in.getTime();
            long totalTime = totalWork - lunchTotal;
            long diffHours = totalTime/HOURS % 24;
            totalTime -= diffHours;
            long diffMinutes = totalTime/MINUTES % 60;
            totalTime -= diffMinutes;

            return String.format("%02d:%02d", diffHours, diffMinutes);
        }
        catch (ParseException e) {e.printStackTrace();}
    }
    else
    {
        try
        {
            if(null == breakStart || null == breakEnd)              {
                in = timeFormat.parse(inTime.getStringCellValue());
                out = timeFormat.parse(outTime.getStringCellValue());

                long totalTime = out.getTime() - in.getTime();
                long diffHours = totalTime/HOURS % 24;
                totalTime -= diffHours;
                long diffMinutes = totalTime/MINUTES % 60;
                totalTime -= diffMinutes;

                return String.format("%02d:%02d", diffHours, diffMinutes);
            }
            else if(null == inTime.getStringCellValue())
            {
                System.out.println(LOG + "inTime is blank");
                return "-1";
            }
        }
        catch (ParseException e) {e.printStackTrace();}
    }
    return "-1";
}