面向对象设计中的开放封闭原则

//首先声明一个业务处理接口

public  interface IBankProcess...{  void Process();}
 
public class DepositProcess : IBankProcess
 
    ...{
 
        public void Process()
 
        ...{ //办理存款业务
 
            Console.WriteLine("Process Deposit");
 
        }
 
}
 
public class WithDrawProcess : IBankProcess
 
    ...{
 
        public void Process()
 
        ...{ //办理取款业务
 
            Console.WriteLine("Process WithDraw");
 
        }
 
}
 
public class TransferProcess : IBankProcess
 
    ...{
 
        public void Process()
 
        ...{ //办理转账业务
 
            Console.WriteLine("Process Transfer");
 
        }
 
    }
 
public class BankStaff
 
    ...{
 
        private IBankProcess bankpro = null;
 
        public void BankHandle(Client client)
 
        ...{
 
            switch (client.Type)
 
            ...{   //存款
 
                case "Deposit":
 
                    userProc = new DepositUser();
 
                    break;
 
                    //转账
 
                case "Transfer":
 
                    userProc = new TransferUser();
 
                    break;
 
                    //取款
 
                case "WithDraw":
 
                    userProc = new WithDrawUser();
 
                    break;
 
            }
 
            userProc.Process();
 
        }

    }

//这样当业务变更时，只需要修改对应的业务实现类就可以，其他不相干的业务就不必修改。当业务增加，只需要增加业务的实现就可以了。