With adaptive optimizing: https://en.wikipedia.org/wiki/Java_performance#Adaptive_opti...

What? It's been open source for years!

I was under the impression that only some parts of the JVM was open and that the high performance server implementations have always been proprietary?

The (old) Oracle JRockit is not really better. It was, but it was probably getting really troublesome to maintain, and with buying Sun they probably felt that it was rather redundant. (There was no need for a clean room implementation since they owned all relevant IP anyhow.)

Not at all.