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XAL (that is JFC/Swing) and SWT/Jface applications may be used on any X11 equipped workstation (Windows PC, Solaris) with some performance degradation because JFC/Swing performs poorly over X11 (even in Java >=1.4). These apps could be run "natively" on Windows (since Swing is pure Java, which is platform independent, and any SWT components could be delivered for Windows too). However, the added complexity of synchronizing filesystem resources between the Unix filesystem and the Windows filesystem probably makes this option undesirable - see Redflags. Hence, Proposal: no native Windows apps, Windows only over X.
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