static void Main(string[] args)
{
SchoolRing sr = new SchoolRing();
Student stu = new Student();
stu.SubscrbeToRing(sr);
Console.WriteLine("请输入打铃参数（1.表示打上课铃，2表示打下课铃）：");
int ringKing = Convert.ToInt32(Console.ReadLine());
sr.Jow(ringKing);
Console.ReadKey();
}
public void CancelSubscrbe(SchoolRing schoolRing)
{
schoolRing.onBellSound -= SchoolJow;
}
//退订与订阅
public void SubscrbeToRing(SchoolRing schoolRing)
{
schoolRing.onBellSound += SchoolJow;
}