如何计算时间差？

static Calendar getCalendar(String time)
??? {
??????? if (null == time)
??????? {
??????????? return null;
??????? }
??????? String[] times = time.split("-");
??????? Calendar calendar = Calendar.getInstance();
??????? calendar.set(Integer.valueOf(times[0]), Integer.valueOf(times[1]), Integer.valueOf(times[2]));
??????? return calendar;
??? }
???
??? public static void main(String[] args)
??? {
??????? String startTime1 = "2011-03-02";
??????? String startTime2 = "2011-03-17";
??????? Calendar c1 = getCalendar(startTime1);
??????? Calendar c2 = getCalendar(startTime2);
???????
???????
??????? System.out.println("相差天数："
??????????????? + (c2.getTimeInMillis() - c1.getTimeInMillis())/1000*60*60*24;
}