Why all the java code is packed in Classes?

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 ins开发者_开发知识库ide some class in Java ? Why it does not have independent functions ?

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.

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).

Because that's how the designers of the language wanted it to be.

Java enforces the Object Oriented paradigm very very heavily. That said, there are plenty of ways to work around it if you find it cumbersome.

For one, the class that contains main can easily have lots of other methods in it. Also, it's not uncommon to make a class called 'Utility' or something similar to store all your generic methods that aren't associated with any particular class or objects.

If you work in a smart IDE such as eclipse, you'll eventually find that Java's seemingly over-abundant restrictions, exceptions, and rigorous structure are actually a blessing in disguise. The compiler can understand and work through your code much better when the language isn't cluttered with syntactic junk. It will give you information about unused variables and methods, dead code, etc. and the IDE will give you suggested fixes and code completion (and of course auto-format). I never actually type out import statements anymore, I just mouse over the code and select the class I want. With rigorous types, generic types, casting restrictions etc. the compiler can catch a lot of code which might otherwise result in all kinds of crazy undetectable behavior at runtime. Java is the strictest language in the sense that most of what you type will not compile or else very quickly throw an Exception of one kind or another. So, if you ask a question about the structure of Java, Java programmers will generally just answer "because that's the rule" while Python programmers are trying to get their indentation right (no auto-format to help), Ruby programmers are writing unit tests to make sure all their arguments are of the correct type and C programmers are trying to figure out where the segfault is occuring. As I understand C++ has everything Java has, but too many other capabilities (including casting anything to anything and oh-so-dangerous pointer arithmetic).

And you can have multiple entry points in a jar depending on how many classes inside the package has main.