This has been discuss many time in this forum. Do a google search of "maemo java" and you'll get some good hits to pages that tell you how this can be done. There's also a wiki page in Maemo.org (under community tob) that give some additional information. Be aware, that there is no plug-in for the web browser to be able to do java applets in the browser.
If run java smooth, it 'opens a door' to lot of apps, more functions and a 'new' life for some nits...