java变量

吓得我赶紧搜了下面向对象三要素：封装继承多态，然后写了代码进行测试，终于得出结论：Rabbit obj = new Giraffe();能够过编译器这关。作者的多态没理解透彻啊

class Rabbit {}class Giraffe extends Rabbit {}public class Object {    public static void main(String[] args) {        Rabbit obj = new Giraffe();    }}