单例模式以及观察者模式的编写

//单例模式

public class Single {//使用同步锁防止多个线程同时访问这个单例
    private static Single single;
    private static Object obj = new Object();
    private Single() { }
    public static Single shareSingle() {
        if (single == null) {
            lock (obj) {
                if (single == null) {
                    single = new Single();
                }
            }
        }
        return single;
    }
}

//观察者模式

 class Class2
    {
        static void Main(string[] args)
        {
            Customer subject = new Customer();
            Accountant accountant = new Accountant(subject);
            Cashier cashier = new Cashier(subject);
            Dilliveryman dilliveryman = new Dilliveryman(subject);

            //subject.Update += accountant.GiveInvoice;
            //subject.Update += cashier.Recoded;
            //subject.Update += dilliveryman.Dilliver;

            //subject.CustomerState = "已付款";
            subject.Notify();
            Console.Write(accountant.accountantState);
            Console.Read();
        }
    }
    public interface ISubject
    {
        void Notify();
    }
    public class Customer : ISubject
    {
        private string customerState;
        public delegate void CustomerEventHandler();//声明委托
        public event CustomerEventHandler Update;
        public void Notify()
        {
            if (Update != null)
            {
                Console.WriteLine("我来买东西了");
                Update();
            }
        }
        public string CustomerState
        {
            get { return customerState; }
            set { customerState = value; }
        }
    }

    public class Accountant
    {
        public string accountantState;
        public Accountant(Customer customer)
        {
            customer.Update += GiveInvoice;
        }

        public void GiveInvoice()
        {
            Console.WriteLine("我是会计，我来开具发票。");
            accountantState = "已开发票";
        }
    }

    public class Cashier
    {
        private string cashierState;
        public Cashier(Customer customer)
        {
            customer.Update += Recoded;
        }
        public void Recoded()
        {
            Console.WriteLine("我是出纳员，我给登记入账。");
            cashierState = "已入账";
        }
    }

    public class Dilliveryman
    {
        private string dillivierymanState;
        public Dilliveryman(Customer customer)
        {
            customer.Update += Dilliver;
        }
        public void Dilliver()
        {
            Console.WriteLine("我是配送员，我来发货");
            dillivierymanState = "已发货";
        }
    }