Vast difference in Java Performance from 1.4 to 1.6

Question

I have observed a great difference in Sun Java performance when code is compiled through jdk1.6 as compared to jdk1.5 or jdk1.4 (over 4 folds)

What changes and optimizations have been done? Is there anything worth taking home from these changes which will help to boost our application performance.

Thanks for replying

Answer 1

See: Java SE 6 Performance White Paper.

Answer 2

You might be interested in a recent Java Posse interview with engineers from AMD. They talk about advances in machine architecture and HotSpot over the last few years. They also discuss some benchmarks that match your observations.

The "take-away" from these engineers was that developers can best help HotSpot do its magic by following common idioms and writing straightforward code. Clever optimizations by a developer that work in one release might prevent HotSpot from doing much better optimization in a later version.