Java performance is often considered a black art, and on occasions a process heavily influenced by the particular vendor publishing the results.
In this paper by Dries Buytaert, he explores Java Performance with rigorous statistics.
There exist a wide variety of Java performance evaluation methodologies used by researchers and benchmarkers. These methodologies differ from each other in a number of ways. Some report average performance over a number of runs of the same experiment; others report the best or second best performance observed; yet others report the worst. Some iterate the benchmark multiple times within a single VM invocation; others consider multiple VM invocations and iterate a single benchmark execution; yet others consider multiple VM invocations and iterate the benchmark multiple times.
This paper shows that prevalent methodologies can be misleading, and can even lead to incorrect conclusions. The reason is that the data analysis is not statistically rigorous.
Dries blog: http://buytaert.net/statistically-rigorous-java-performance-evaluation
The complete paper [PDF format] : http://buytaert.net/files/oopsla07-georges.pdf