SWT Spy plugin allows you to convert your existing SWT UI into a wireframe that you can edit and revise afterwards.
To get started, open the dialog or window you want to mockup. Press Alt+Shift+F5 and the XML of the mockup will be copied into the clipboard. Open the “New Screen” wizard, and on the second page paste the XML. Hit Finish and you are done! Note that you can also paste the XML directly into a screen.
Technically Spy functionality is provided as a separate plugin: com.wireframesketcher.spy. You need to make sure that this plugin is included in your environment when you launch your Eclipse plugin or RCP application.
For more information and a video screencast please see the Spy plugin announcement.
There is swing2mockup community project that lets you do the same thing with your Swing UI!
Next: Installing plugins