I don't think Java ever "won" in the cross-platform GUI application space. Sun tried hard and Swing was successful in terms of being able to produce a reliable, cross-platform experience that was reasonable. But in terms of developer mind-share and actual applications on the desktop, I'd say it's success was pretty meager. Aside from IntelliJ and NetBeans and Eclipse (yep, I know, SWT) I'm hard pressed to think of other popular Java GUI applications.