How does VM code compiler works?

Answer 1

The Java virtual machine is not a compiler, it is an interpreter which primarily performs runtime-translation of Java byte code (the native language of the Java virtual machine) to machine-code (the native language of the physical machine).

The Java compiler, on the other hand, is a separate program used to perform compile-time conversion of high-level Java source code to the lower level byte code. Java byte code is highly portable; once compiled, any architecture or platform that implements a JVM can execute the byte code without modification.

Answer 2

The idea is that the bytecode is compiled into native machine language, to make the program run faster than when it is simply interpreted.