Why can outer Java classes access inner class private members?

Question

I observed that Outer classes can access inner classes private instance variables. How is this possible? Here is a sample code demonstrating the same:

class ABC{

    class XYZ{

        private int x=10;

    }

    public static void main(String... args){

        ABC.XYZ xx = new ABC().new XYZ();

        System.out.println("Hello :: "+xx.x); ///Why is this allowed??

    }

}

Why is this behavior allowed?

Answer 1

The inner class is just a way to cleanly separate some functionality that really belongs to the original outer class. They are intended to be used when you have 2 requirements:

1. Some piece of functionality in your outer class would be most clear if it was implemented in a separate class.
2. Even though it's in a separate class, the functionality is very closely tied to way that the outer class works.

Given these requirements, inner classes have full access to their outer class. Since they're basically a member of the outer class, it makes sense that they have access to methods and attributes of the outer class -- including privates.