static void Main(string[] args)
{
//创建工厂对象
UndergraduateFactory uFactory = new UndergraduateFactory();
VolunteerFactory vFactory = new VolunteerFactory();
//工厂返回雷锋（父类） 实际上是子类
LeiFeng undergraduate = uFactory.CreateLeiFeng();
LeiFeng volunteer = vFactory.CreateLeiFeng();
undergraduate.Sweep();
volunteer.BuyRice();
Console.ReadKey();
}
static void Main(string[] args)
{
IFactory factory = new UndergraduateFactory();
LeiFeng student = factory.CreateLeiFeng();
}