Bug#251494: libgcj4-dev: conflicts with (ancient!) libgcj0
> Package: libgcj4-dev
> Version: 1:3.3.3-9
> Severity: minor
> My libgcj0 version was 2.95.1-5 i.e. quite old. The good thing is, my
> debian machine apparently survived all that time :)
> The single conflicting file is:
> A simple Conflicts: entry should solve the problem, I think.
> Unfortunately, I can not check it anymore, since I wiped the package a
> bit too fast.
that is a pre-woody version; in general Debian only supports direct
updates to the next distribution.