these helped a lot in understanding it.

In this case,

- what is a jar file? (how different from obj, class or exe?)

- how is obj file different from class/ jar files?

- how to get exe file of java programs? I have seen only
java, class and jar files.

- As everybody does development on one machine, one os, is
it possible to bypass creation of class files, and directly
get the executable, so that it gets executed fast?

After the testing is over, one can send class to other
machines/ other o/s, but in that case too, one would send
.java source and regenerate class file there.

In that case, what is the purpose of that intermediate stage
having class files.