The Sun Java JIT compiler, an integral part of the Solaris JVM, can accelerate execution performance many times over previous levels. Long-running, compute-intensive programs show the best performance improvement.
When the JIT compiler environment variable is on (the default), the JVM reads the .class file for interpretation and passes it to the JIT compiler. The JIT compiler then compiles the bytecodes into native code for the platform on which it is running. The next figure illustrates the JIT compile process.
The following figure shows the functional relationship of the JIT to the Solaris JVM and JRE.