Beryl XML GUI
The Beryl XML GUI library was written to ease the development of graphical user interfaces using Swing on Java. It lets you store user interfaces as XML markup. This will help you avoid unnecessary clutter in your source - Swing code mixed with application logic can become a troublesome and hard to read mess as the application size increases. The library comes with a visual component builder, which makes development a breeze.
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License
GNU Library or Lesser General Public License (LGPL)