How can I (natively) implement the fullscreen feature of OSX Lion in a Java application?
The current answers given incorporate a good method for achieving a sort-of-
Java allows you full screen mode, that has nothing to do with Lion. (via chubbard)
If you want to write native Cocoa applications with Java, you need to use JavaBridge. However, JavaBridge is deprecated.
My recommendation is: If you want to write native OSX Cocoa applications, do it in Objective C or Macruby. MacRuby is currently receiving funding from Apple (Sansonetti is a full-time Apple employee) and might just have a future with Cocoa. Java doesn't.