CodenameOne supports generating a "preview MIDlet" on the fly to allow designers to preview their UI on an actual device. This requires some work to configure for the first time and isn't intended as a "production" tool, however once configured this is an immensly powerful tool for a designer providing the designer with the "feel" of the theme on a specific device.
Running on Nokia devices requires the Nokia PC suite which is used to upload the resulting application directly to the device.
When running the wizard for the first time one has to point to the directory where the PC suite is installed if it was not installed at the default location. A Nokia device needs to be connected to the machine with a USB cable or bluetooth to get this to work.
When a UI is executed on the device a combo box is presented allowing you to pick the UI form to start with. This is useful for a designer to preview starting from an arbitrary form in the middle of the application and not necessarily going through the full application flow which might not be applicable without application code.