?class?Animal?{ public?String?name; Animal?(String?name)?{ this.name?=?name; }}?class?Dog?extends?Animal?{ public?String?furColor; Dog(String?n,String?c)?{ super(n);c?=?furColor; }}public?class?Test?{ public?static?void?main(String?args[])?{ Animal?a?=?new?Animal("name"); a?=?new?Dog("bigyellow","yellow"); System.out.println(a.name); Dog?d1?=?(Dog)?a; System.out.println(d1.furColor); }}請(qǐng)問(wèn)為啥這里我寫(xiě)c?=?furColor; ?d1.furColor輸出結(jié)果為null, ?寫(xiě)成furColor=d1輸出結(jié)果就是yellow呢？