java 内部类可以被覆盖吗

如果创建了一个内部类,然后继承其外围类并重新定义内部类时,"覆盖"内部类就好像是其外围类的一个方法,并不起作用,

这两个内部类是完全独立的两个实体,各自在自己的命名空间内

//: innerclasses/BigEgg.java
// An inner class cannot be overriden like a method.
import static net.mindview.util.Print.*;

class Egg {
  private Yolk y;
  protected class Yolk {
    public Yolk() { print("Egg.Yolk()"); }
  }
  public Egg() {
    print("New Egg()");
    y = new Yolk();
  }
}    

public class BigEgg extends Egg {
  public class Yolk {
    public Yolk() { print("BigEgg.Yolk()"); } //这里并没有输出
  }
  public static void main(String[] args) {
    new BigEgg();
  }
} /* Output:
New Egg()
Egg.Yolk()
*///:~

当然,明确的继承某个内部类也是可以的

//: innerclasses/BigEgg2.java
// Proper inheritance of an inner class.
import static net.util.Print.*;

class Egg2 {
  protected class Yolk {
    public Yolk() { print("Egg2.Yolk()"); }
    public void f() { print("Egg2.Yolk.f()");}
  }
  private Yolk y = new Yolk();
  public Egg2() { print("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 { //通过继承明确的继承了Egg2.Yolk类,并覆盖了其中的方法
    public Yolk() { print("BigEgg2.Yolk()"); }
    public void f() { print("BigEgg2.Yolk.f()"); }
  }
  public BigEgg2() { insertYolk(new Yolk()); }//向上转型成Egg2.Yolk类
  public static void main(String[] args) {
    Egg2 e2 = new BigEgg2();
    e2.g();
  }
} /* Output:
Egg2.Yolk()
New Egg2()
Egg2.Yolk()
BigEgg2.Yolk()
BigEgg2.Yolk.f()
*///:~