As I also wanted to use To-Do-O (which uses Java and SWT) on my N900 I started to port SWT to the Hildon UI as used in Fremantle. The result is called libswt-hildon and is available in the extras-testing repository in binary form and on the Maemo garage site in source form as one big patch.
The whole thing started off with a simple patch taken from https://evolvis.org/plugins/mediawiki/wiki/jalimo/index.php/Maemo. During the development I added many more features like support for the touch UI, native Hildon dialogs or support for the Fremantle version of Mozilla Firefox (Fennec). For more details please see the linked thread below and the patch itself.
This all was possible as Hildon essentially extends GTK and SWT ships with a GTK version as well. So much of the work was to figure the Hildon additions to GTK out and how to meaningfully integrate these with SWT. During this work I learned quite a lot about GTK, Hildon, the GObject system, SWT, and JNI. 🙂
The Maemo garage site is located at: https://garage.maemo.org/projects/swt-hildon
A talk.maemo.org thread about this is located at: http://talk.maemo.org/showthread.php?t=40778