From the Functional Overview of (Eclipse) Visual Editor:
The Eclipse Visual Editor (VE) can be
used to open any .java file. It then
parses the Java source code looking
for visual beans. ...
Some visual editing tools will only
provide a visual model of code that
that particular visual tool itself has
generated. Subsequent direct editing
of the source code can prevent the
visual tool from parsing the code and
building a model.
Eclipse VE, however, ... can either be
used to edit GUIs from scratch, or
from Java files that have been
'hardcoded' or built in a different
visual tool. The source file can
either be updated using the Graphical
Viewer, JavaBeans Tree or Properties
view or it can be edited directly by
the Source Editor.
Maybe I should stick with Matisse for now.
Unrelated, here's someone asking for the halting problem within Eclipse.
To be fair, VE's domain is quite limited, and it probably won't go crazy over tricky things like reflection. Still, the claim to build GUI out of any java file seems halt-ish.
