Right now two ways come to my mind.

First: 
       Create a TreeSet, add all the dates to it. They get 
sorted by default since java.util.Date implements 
comparable. Here is an example -->
       Set<Date> sortedDates = new TreeSet<Date>();
       sortedDates.add(new Date());
       Calendar cal = Calendar.getInstance();
       cal.set(2009, 2, 12);
       sortedDates.add(cal.getTime());

Second: 
        We can use the compare method inside Date class 
directly and write our own sorting implementation.