Why all the java code is packed in Classes?

Question

I have started learning Java and picked up some books and collected materials online too. I have programmed using C++. What I do not understand is that ,even the main method is packed inside a Class in Java. Why do we have everything packed inside some class in Java ? Why it does not have independent functions ?

Answer 1

This is the main concept of object oriented programming languages: everything is an object which is an instance of a class.

So because there's nothing but classes in Java (except the few Java primitive types, like int, float, ...) we have to define the main method, the starting point for a java application, inside a class.

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The main method is a normal static method that behaves just like any other static method. Only that the virtual machine uses this one method (only) to start the main thread of the application.

Basically, it works like this:

1. You start the application with java MyClass
2. The JVM loads this class ("classloading")
3. The JVM starts a new thread (the main thread)
4. The JVM invokes the method with the signature public static void main(String[])

That's it (in brief).