Before I start, I would like to share with you a nice video which greatly enhanced my understanding about Java.



It's ok if you still don't get the whole picture. Now read these....

"Java was designed with a concept of ‘write once and run everywhere’. Java Virtual Machine (JVM) plays the central role in this concept. The JVM is the environment in which Java programs execute. It is a software that is implemented on top of real hardware and operating system.

When the source code (.java files) is compiled, it is translated into byte codes and then placed into (.class) files. The JVM executes these bytecodes. So Java byte codes can be thought of as the machine language of the JVM." - source javabeginner.com

Now watch the video again to understand better. Follow "Hello World!" program and try how Java work for the first time.