I’ve been seeking for a a while the « good tool for modelising UML in Java » or other languages .
The best tool I’ve found from now is eUML2 .In the version PRO we can have automatically pop out the sequence diagram which help us to have a good understanding and drill down on what we are working on .
Generaly the documentation is taken for granted in an IT projet, but I think it’s important to keep a good, clear prompt documentation so that we can maintain a certain level of quality and coherence during the time in a project or program.

Source

for win7 x64 + eUML2 Free Edition 3.6.0.20110120 + required plugins for Helios/Eclipse 3.6.x

1/ install eclipse
2/ install new plugin : help > install new software
select work with : Helios – http://download.eclipse.org/releases/helios
write EMF in field below work with
install EMF – Eclipse Modeling Framework SDK
restart eclipse
3/ install new plugin : help > install new software
select work with : Helios – http://download.eclipse.org/releases/helios
write GMF in field below work with
install Graphical Modeling Framework (GMF) Runtimes
restart eclipse
3/ download
eUML2-free-Edition-3.6.0.20110120+dependencies_for_eclipse3.6.zip
from eUML2 website
in eclipse install new plugin : help > install new software
click add > archive and browse to your downloaded file
follow installation process
restart
your done

Maybe another way is to do (but I did not try it) for step 3/
clic add
enter http://www.soyatec.com/update/galileo/
follow installation process
restart