Java-私有内部类公共成员

Question

how does the access level modifier change the behavior of a member inside an inner private class? I have this code

class Main {
    private static class Inner {
        private static int a = 1;
    }
    public static void main(String[] args) {
        System.out.print(Inner.a);
    }
}

I can access the attribute "a" from the outer class either it's access level is public or private (and this is already weird for me). The question is: if the attribute were " public static int ", what were the difference (considering that the Inner class is private so inaccessible from the extern of the "Main" class)?

To recap

• The attribute is private: I can access it from Main but not from outside Main (because Inner is private)
• The attribute is public: I can still access it from Main but not from outside Main (because Inner is private)

I can see no difference

Answer 1

Inner is private, it can be accessed only from within Main . Even if a is public, but Inner is private and cannot be accessed from a particular place, attribute of a would be irrelevant.

class Main {
    private static class Inner {
        public static int a = 1;
    }
    public static void main(String[] args) {
        System.out.print(Inner.a);
    }
}

When you run ,

1

Whenever Inner is static in the same class,( Main ), Inner (and all its members) are always accessible from anywhere in the Main class. It is private outside of Main Class. If I were to access

Main main = new Main();
main.Inner; // Compilation Failure. Inner is not accessible
// Technically I would never do new Main(), but to illustrate I am doing so.

Or a more sensible example of the same

class Main {
    public static void main(String[] args) {
        System.out.print(SomeClass.Inner);
    }
}

class SomeClass{
    private static class Inner {
        public static int a = 1;
    }

}

To illustrate the difference of making a private or public, consider the following two examples

class Main {
    public static void main(String[] args) {
        System.out.print(SomeClass.Inner.a);
    }
}

class SomeClass{
    public static class Inner {
        private static int a = 1;  // If a is private, it produces an error above
      //public static int a = 1; // This would not be an error
    }
}

So in your particular case, as long as it is in same class Main , it is irrelevant, but if it is outside as next example, it would matter.

Answer 2

You can think of your Inner class as a class-level attribute. Making it private prevents access to it outside of the class. Since it's an inner class, the inner class's variables belong to the outer class and are thus accessible to the outer class, regardless of the access modifiers.

http://docs.oracle.com/javase/tutorial/java/javaOO/innerclasses.html