What is a JIT compiler?
A Just-In-Time compiler is one way to implement the Java Virtual Machine. Rather than the typical, pure interpreter, a JIT compiler will, on demand, compile the platform independent Java byte codes into platform specific executable code, in real-time. The first time through, the byte codes are compiled before being executed. Future passes will use a cached version of the compiled code. This tends to result in a performance increase of 10-100 times, depending upon the task at hand, over purely interpreted byte codes.