关于内部类是否会被覆盖的理解（thinking in java ）

 1 package thinkingDemo;
 2 /*
 3  * 
 4  * 关于嵌套类覆盖问题
 5  * 
 6  */
 7 class Egg2 {
 8     protected class Yolk{
 9         public Yolk(){
10             System.out.println("Egg2.Yolk()");
11         }
12         public void f(){
13             System.out.println("Egg2.Yolk.f()");
14         }
15     }
16     private Yolk y = new Yolk() ;
17     public Egg2(){
18         System.out.println("New Egg2()");
19     }
20     public void insertYolk(Yolk yy){
21         y = yy ;
22     }
23     public void g(){
24         y.f() ; 
25     }
26 }
27 class BigEgg2 extends Egg2 {
28     public class Yolk extends Egg2.Yolk {
29         public Yolk(){
30             System.out.println("BigEgg2.Yolk()");
31         }
32         public void f(){
33             System.out.println("BigEgg2.Yolk.f()");
34         }
35     }
36     public BigEgg2(){
37         insertYolk(new Yolk()) ;
38     }
39 }
40 public class NestClassOverride {
41     public static void main(String[] args) {
42         Egg2 e2 = new BigEgg2() ;
43         e2.g() ;
44     }
45 }