void ModelA::fly(const Airport &destination)//子类必须实现父类的pure virtual函数. { cout<<"ModelA::fly to"<<destination.getPortName()<<endl; }
void ModelB::fly(const Airport &destination) { cout<<"ModelB::fly to"<<destination.getPortName()<<endl; }
void Airplane::fly(const Airport & destination)//父类中的pure virtual函数自己的实现 { cout<<destination.getPortName()<<endl; }