（1）实现单重继承并借助接口实现多重继承。

（2）实现方法的继承与重写。

（3）实现方法的重载。

（4）实现对象的上转及接口的回调。

-(1) for single re-use of interface inheritance and multiple inheritance. (2) Implementation of the inheritance and override. (3) the realization of the overload. (4) to achieve the object and the interface on the transfer callback.