计算两个日期之差

从网上找到的一个小程序，转载一下：

01	import java.util.Calendar;
02	  
03	public class DateDifferent{   
04	    public static void main(String[] args){
05	    Calendar calendar1 = Calendar.getInstance();
06	    Calendar calendar2 = Calendar.getInstance();
07	    calendar1.set(2007, 01, 10);
08	    calendar2.set(2007, 07, 01);
09	    long milliseconds1 = calendar1.getTimeInMillis();
10	    long milliseconds2 = calendar2.getTimeInMillis();
11	    long diff = milliseconds2 - milliseconds1;
12	    long diffSeconds = diff / 1000;
13	    long diffMinutes = diff / (60 * 1000);
14	    long diffHours = diff / (60 * 60 * 1000);
15	    long diffDays = diff / (24 * 60 * 60 * 1000);
16	    System.out.println("\nThe Date Different Example");
17	    System.out.println("Time in milliseconds: " + diff + " milliseconds.");
18	    System.out.println("Time in seconds: " + diffSeconds + " seconds.");
19	    System.out.println("Time in minutes: " + diffMinutes + " minutes.");
20	    System.out.println("Time in hours: " + diffHours + " hours.");
21	    System.out.println("Time in days: " + diffDays + " days.");
22	  }
23	}