在包vehicle中，建一个Vehicle的类motorvehicle和bike继承Vehicle,car和motorcycle继承motorvehicle，racingbike和tandembike继承bike。usedcar和cardealer是接口机制实现的，Myvehicle是主函数。gui包是另外作的一个界面。Insurance包是car类的保险业务-Vehicle in the package, the construction of a Vehicle class motorveh