The way you do this is modify the auto-mode-alist
to point to JDE rather than java-mode like so...
(setq auto-mode-alist
(append
'(("\\.java\\'" . jde-mode))
auto-mode-alist))
the only thing is that JDE should do this for you
automatically when its loaded (the code above is stolen from
jde.el!). You need to work out why this isnt working in your case.
Possibilities that I can think of are incorrect installation of JDE
(do you forcably load it in your .emacs) or over-riding JDE's attempt
to point to it by for instance
(setq auto-mode-alist
(append
'(("\\.java\\'" . java-mode))
auto-mode-alist))
or something similiar in your .emacs.
If you cant work it out then send more details of your setup.
See info on the website about what you need to send
(sunsite.auc.dk/jde)
Phil