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The working code you posted does not use the ServerGUI class. The ServerGUI class is the one throwing the Exception. You should contact whoever created the ServerGUI class to see why it throws that...

I mean wherever you're getting the ServerGUI class. That's what's throwing the error.

What library is this?

It looks like whatever library you're using has a method that throws an Exception to tell you that the method isn't supported yet. This isn't a Java question; it's a question...