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By Extending GregorianCalendar PersianCalendar supports:
Converting Gregorian to Persian Calendar system and vice versa.
Adding Years, Months, Days, Hours, Minutes etc to the current date
Parsing string and produce PersianCalendar?!
future release!
Swing base DateTime? picker component
GWT DatePicker? component
see how to use: http://code.google.com/p/persian-calendar/wiki/ExampleUsage
or read : https://sourceforge.net/p/persian/wiki/