What if main method is inside “non public class” of java file?

Question

I have a java file containing more than one class, out of which one is public. If main method is inside a non-public class. I can\'t run that java file. Why is that? and the

Answer 1

Have a look at this code:
Super.java

public class Super{ }
class Sub{
    public static void main(String[] s){
        System.out.println("Hello");
    }
}

In order to print Hello you can compile and run the program as:

How this works?
The compiler generates separate .class file for every class in your program. So, instead of calling the main() of non-public class from the public class's main() you can print the output as shown above.

Note: As the convention says, you must put a public class in separate file .java. And do not put more than one class in a single file (except if they are inner class) because if you would like to import them or use them with other classes then it will cause problem.