If you are interested in using Java for high performance / low latency applications (such as financial applications), you might want to look into the Disruptor project, used by LMAX:

http://code.google.com/p/disruptor/

http://martinfowler.com/articles/lmax.html

http://www.infoq.com/presentations/LMAX

I discovered this project thanks to gaius who mentioned it here: http://news.ycombinator.com/item?id=2785195