Re: a question about factory method

     As to *how* a factory method might choose which of several classes
to return, you already illustrated one way (paraphrased):

     public static Calendar getInstance(Date aDate, int choice) {
         if (choice == 1) {
             ... //return a GregorianCalendar object
         } else if (choice == 2) {
             ... //return a MayanCalendar object
         } else if (choice == 3) {
             ... //return a JulianCalendar object
         } else {
             return null;
         }
     }

To me, this doesn't seem a huge advantage: The caller who writes
`getInstance(date, 2)' could just as easily write `new MayanCalendar()'
with about the same effect.