The manpage says:
than one input file is specified, all must currently be
".java" files, though we hope to fix this.)
I think this limitation has been removed.
Also, shouldn't .o files appear in the list of supported input files?
I can confirm that this behavior is still present in gcc 3.3 branch and mainline (20030525)
(leastaways, the docs read the same).
See Dara's comment.
The limitation was removed a long time ago.