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 }