内部类的继承与应用示例

class Egg2{protected class Yolk{public Yolk()//第2步，第7步{System.out.println("Egg2.Yolk()");}public void f(){System.out.println("Egg2.Yolk.f()");}}private Yolk y = new Yolk();//第1步， 加载类时将非静态变量加载public Egg2()//第3步，调用构造函数{System.out.println("New Egg2()");}public void insertYolk(Yolk yy)//第6步{y = yy;}public void go(){y.f();}}class BigEgg2 extends Egg2{public class Yolk extends Egg2.Yolk{public Yolk()//第8步{System.out.println("BigEgg2.Yolk()");}public void f(){System.out.println("BigEgg2.Yolk.f()");}}public BigEgg2()//第4步，调用构造函数{insertYolk(new Yolk());//第5步}public static void main(String[] args){Egg2 e2 = new BigEgg2();e2.go();//y此时指向BigEgg2对象（在第5步中已确定BigEggy的引用向上转型为Egg2），所以调用的是BigEgg2中的f()}}