Inner processsing of java program

Explaining the Hello World! program.

First consider the Hello World program shown below.

First of all note that we named the file as Hello.java and also named the class (which I will explain later) also as Hello. So is this a coincidence? Well the answer is no! .Because particularly in java every line of code should reside inside a class and the rule is the name of the class should match the file name in which the program is written. Well the reason is just to make your programs organized and it would give you the picture of what this class does. Here Hello.java is the program name and its use is to print Hello World! Statement

Note: Always remember that java is case sensitive.

Now when you compiled your first java program you see a file named with .class extension named Hello.class.

So, what is a .class File and who created this?

The answer is javac compiler created this file Hello.class which contains the bytecode version of the program that you have written.

Note that javac only gives you a bytecode version of the program but not the actual machine level code that could be executed in a machine. To run the program you need to invoke the java application launcher and we write something like

java  Hello

The above statement is to invoke java application launcher and pass the

JVM executes the bytecode version of the program and gives us the output. So this makes java as PLATFORM INDEPENDENT LANGUAGE .

The bytecode version of Hello World program would look like this.

.class file Hello to the Java Virtual Machine(JVM) as an argument and

JVM executes the bytecode version of the program and gives us the output. So this makes java as PLATFORM INDEPENDENT LANGUAGE .

The bytecode version of Hello World program would look like this.

In next post we will discuss every line of code.