Package-private class within a .java file - why is it accessible?

Question

Consider the following code, where the HelloWorld class has default or package-private access:

class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello World!"); // Display the string.
    }
}

And assume that the above code is saved in a file called HelloWorld.java. So my question is: since HelloWorld is now a package-private class, how does it work? The main() method should not be visible or accessible across packages, am I right?

It makes perfect sense to me if the class HelloWorld is declared public. Confusion is only when it is declared with the default package-private access.

Answer 1

JVM startup is described in §12.1 Virtual Machine Start-Up of the JLS.

Note that this chapter says nothing about visibility checks with regards to the class. It only specifies that the main method must be public.

This means that there simply is no check for visibility on the class level (which kind-of makes sense as there is no context yet against which to check the visibility: in which "package" is the "caller"?).

Answer 2

Main method won't be visible to other classes which reside in different packages. But the JVM can see it all. It won't have any difficulty in finding your main method and running it for you.

If you want to simulate the access restriction, write another class in a different package and try to call HelloWorld.main and see if the compiler keeps quiet.