Nested classes can access all members of all levels of the classes they are nested within : Nested Classes « Class Definition « Java Tutorial

1. Java Tutorial
2. Class Definition
3. Nested Classes

class MyClass {
  private void f() {}
  class A {
    private void g() {}
    public class B {
      void h() {
        g();
        f();
      }
    }
  }
}

public class MainClass {
  public static void main(String[] args) {
    MyClass a = new MyClass();
    MyClass.A innerA = a.new A();
    MyClass.A.B innerb = innerA.new B();
    innerb.h();
  }
}