hvjavacalendar
hvajavacalendar is a Java package that has many calendars
...):
Bohemia and Moravia, Great Britain and Dominions, Bulgaria, Denmark,
Norway and many German Protestant states, Finland and Sweden, Hungary,
Luxemburg, Prussia, Romania, Russia, Estonia, Swiss Protestant
cantons.
The classes do not implement the java.util.Calendar interface (perhaps
they should :-) but they have functions to convert to and from
java.util.GregorianCalendar.