No, there isn't a source code search on the website, at least as far as I know.
When I used Windows, if I was already on the command line, I prefer using
ack to search files, which is a perl script that was written to search code. It color-codes the matches like Grep on *NIX systems does without any additional configuration, and it ignores all the .svn folders by default (though if you're using git-svn instead, that's a minimal bonus), so I really enjoyed it.
Otherwise, the native Windows search UI is very good. Just right-click on the folder you want to search, restrict your searches to *.java and you're good to go. In my experience on different operating systems, only Spotlight on OSX tops it. Nothing on Linux comes close, though Linux was built for people who love staying on a CLI, so that's not surprising at all.
All that being said, IDEs and programmer-oriented text editors are also pretty good about implementing search interfaces. Eclipse searching is a bit slow on large code bases, but the results are really friendly and right-click searching for references is awesome (available in any decent IDE). Search in a programmer-oriented text editor like
Sublime Text (which I purchased when I went to Xubuntu after Vista drove me crazy) is faster since it feels like it's using grep or something perl-ish in the background, but the results show up in a way that's much less friendly than a real IDE.