Compute the difference between two dates

public class DateDiff {
         public static void main(String[] av) {
         /** The ending date. This value
         * doubles as a Y2K countdown time.
         */
         Date d1 = new GregorianCalendar(1999,11,31,23,59).getTime();
        
         /** Today's date */
         Date d2 = new Date();
        
         // Get msec from each, and subtract.
         long diff = d2.getTime() - d1.getTime();
        
         System.out.println("Difference between " + d2 + "\n" +
         "\tand Y2K is " +
         (diff / (1000*60*60*24)) +
         " days.");
     }
}