Thinking in Java 4th 第10章内部类 10.10内部类可以被覆盖吗 第二个示例的分析

class Egg2 {
        protected class Yolk {
                public Yolk() { 
                        System.out.println("Egg2.Yolk()"); 
                }
                public void f() { 
                        System.out.println("Egg2.Yolk.f()");
                }
        }
        
        private Yolk y = new Yolk();
        
        public Egg2() {
                System.out.println("New Egg2()");
        }
        
        public void insertYolk(Yolk yy) {
                y = yy;
        }
        public void g() {
                y.f();
        }
}
public class BigEgg2 extends Egg2 {
        public class Yolk extends Egg2.Yolk {
                public Yolk() {
                        System.out.println("BigEgg2.Yolk()");
                }
                public void f() {
                        System.out.println("BigEgg2.Yolk.f()");
                }
        }
        
        public BigEgg2() {
                insertYolk(new Yolk());
        }
        
        public static void main(String[] args) {
                Egg2 e2 = new BigEgg2();
                e2.g();
        }

}