Performance tuning Java

Here is a centralized location for information on performance tuning the JVM: http://java.sun.com/javase/technologies/performance.jsp.

Specifically, here is a great white paper on tuning ideas that include some great examples.

I have to admit I am rather new to this subject, but am really interested in learning more. From what I have read and also learned from my co-worker Travis Chase, the best and simplest improvement you can make is running your JVM with the -server option. Most likely your JDK came with the default -client set which starts up faster for development reasons, but should be switched to -server for better performance in production environments. However, before you start performance tuning be mindful of the Ergonomic settings which automatically set your defaults. For example for Window users (32-bit) the -client option is automatically set. Here is some more information on Ergonomics for Java 5.0.