I would suggest you need to go back to creating an EthiopianCalendar class and running it fom the command line before you try it in a GUI. It would appear from this that there is nothing available, but Googling for Java Ethiopian calendar, and this ad from Google might give you something to use instead.
I would suggest for your class, it looks confusing having that many fields. You should consider an enum for Ethiopian months instead of that switch block. You should avoid if (...) b = true; else b = false; It is bad style; see this link. It is also bad style and error prone to write == true or similar.