What does a JIT compiler do?

Question

I was just watching the Google IO videos and they talked about the JIT compiler that they included in the android. They showed a demo of performance improvements thanks to t

Answer 1

JIT = Just in Time. It's a process whereby a program that would otherwise be interpreted (e.g. Java bytecodes or Javascript code) is converted to native machine code on the fly as it runs to improve performance.

Some of the benefits are the JIT compiler can see the hotspots and apply more aggressive optimisations, it can also take advantage of any extensions the current processor has like SSE2.

This question may have more info: How a JIT compiler helps performance of applications?