import java.util.*;public class ObjectTestDrive {    public static void main(String[] args) {        ArrayList
     
       alist = new ArrayList
      
       ();        Dog d = new Dog();        alist.add(d);        Animal a = alist.get(0);        a.yield();        System.out.println(a instanceof Dog);    }}class Animal {    void yield() {        System.out.println("animal,,,,,,,,,");    }}class Dog extends Animal {    void yield() {        System.out.println("wang!wang!");    }}
      
     

输出结果是：

wang！wang！

true