State模式允许对象在内部状态变化时，变更其行为，并修改其类；
优点：
定位指定状态的行为，并且针对不同状态来划分行为，使状态转换显式进行；
适用：
对象的行为依赖于其状态，并且该对象必须在运行时根据其状态修改其行为；
操作具有大量的以及多部分组成的取决于对象状态的条件语句；
public class Bank
{
private int hour;
private Person person;
public void SetClock(int hour)
{
this.hour = hour;
Console.WriteLine($"现在时间是{hour}点");
if (hour > 8 && hour < 18)
ChangeState(Customer.GetInstance());
else ChangeState(Thief.GetInstance());
}
public void ChangeState(Person person)
{
this.person = person;
person.SayHi();
}
}
public interface Person
{
void SayHi();
}
public class Customer : Person
{
private static Customer customer = new Customer();
public static Customer GetInstance() => customer;
public void SayHi()
{
Console.WriteLine("我是客户，我来取钱");
}
}
public class Thief : Person
{
private static Thief thief = new Thief();
public static Thief GetInstance() => thief;
public void SayHi()
{
Console.WriteLine("我是窃贼，我来偷钱");
}
}
public static void StatePatternTest()
{
Bank bank = new Bank();
int hour = 0;
while (true)
{
bank.SetClock(hour);
hour++;
hour %= 24;
Thread.Sleep(1000);
}
}