Tomas Hurka and I gave a BOF last night presenting "Monitoring and Troubleshooting Java applications using JDK tools". The slides give an overview of the tools in the JDK, summarize the symptom and tools to use to diagnose a few typical performance problems including memory leak, deadlock, high lock contention that we walked through the demos. Check out the documentation, article and other resources listed in the slides that has detailed information.

If you are using JDK 5 or 6 earlier to update 7, you can download Java VisualVM at http://visualvm.dev.java.net/.