多态例子

一）相关类

class?A?...{
?????????public?String?show(D?obj)...{
????????????????return?("A?and?D");
?????????}?
?????????public?String?show(A?obj)...{
????????????????return?("A?and?A");
?????????}?
}?
class?B?extends?A...{
?????????public?String?show(B?obj)...{
????????????????return?("B?and?B");
?????????}
?????????public?String?show(A?obj)...{
????????????????return?("B?and?A");
?????????}?
}
class?C?extends?B...{}?
class?D?extends?B...{}?

（二）问题：以下输出结果是什么？

????????A?a1?=?new?A();
????????A?a2?=?new?B();
????????B?b?=?new?B();
????????C?c?=?new?C();?
????????D?d?=?new?D();?
????????System.out.println(a1.show(b));?? ①
????????System.out.println(a1.show(c));?? ②
????????System.out.println(a1.show(d));?? ③
????????System.out.println(a2.show(b));?? ④
????????System.out.println(a2.show(c));?? ⑤
????????System.out.println(a2.show(d));?? ⑥
????????System.out.println(b.show(b));???? ⑦
????????System.out.println(b.show(c));?????⑧
????????System.out.println(b.show(d));???? ⑨????

（三）答案

????????????? ①?? A?and A
????????????? ②?? A and A
????????????? ③?? A and D
??????????????④?? B and A
????????????? ⑤?? B and A
????????????? ⑥?? A and D
????????????? ⑦?? B and B
????????????? ⑧?? B and B
????????????? ⑨?? A and D

?

转摘http://blog.csdn.net/thinkGhoster/article/details/2307001