大话设计-简单工厂

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实现简单计算器的加减乘除运算，做到可维护、可扩展、可复用、且灵活。

可维护举例：业务人员要求加法功能只允许绝对值相加，这时修改代码的区域应只有加法，附近没有其他运算，避免不小心改到了别的运算。

可扩展举例：加个开平方根运算，添加代码的区域附近没有其他运算。

这个简单工厂用于返回运算的实例、每当有新的运算加入，工厂里的switch分支也要添加。

using System;

namespace ConsoleApp4
{
    class Program
    {
        public static void Main(string[] args)
        {
            var operation = OperationFactory.GetOperation("+");
            operation.NumberA = Convert.ToDouble(Console.ReadLine());
            operation.NumberB = Convert.ToDouble(Console.ReadLine());
            Console.WriteLine(operation.GetResult());

            Console.ReadLine();
        }
    }

    //运算基类
    public class Operation
    {
        private double numberA;
        public double NumberA
        {
            get { return numberA; }
            set { numberA = value; }
        }

        private double numberB;
        public double NumberB
        {
            get { return numberB; }
            set { numberB = value; }
        }

        public virtual double GetResult()
        {
            double result = 0;
            return result;
        }
    }
    public class OperationAdd : Operation
    {
        public override double GetResult()
        {
            return NumberA + NumberB;
        }
    }

    public class OperationSub : Operation
    {
        public override double GetResult()
        {
            return NumberA - NumberB;
        }
    }

    public class OperationMul : Operation
    {
        public override double GetResult()
        {
            return NumberA * NumberB;
        }
    }

    public class OperationDiv : Operation
    {
        public override double GetResult()
        {
            if (NumberB == 0)
            {
                throw new DivideByZeroException();
            }
            return NumberA / NumberB;
        }
    }

    // 简单工厂
    public class OperationFactory
    {
        public static Operation GetOperation(string operation)
        {
            switch (operation)
            {
                case "+":return new OperationAdd();
                case "-":return new OperationSub();
                case "*":return new OperationMul();
                case "/":return new OperationDiv();
                default:return new Operation();
            }
        }
    }
}

 超市结账优惠，打折或满减。

using System;

namespace ConsoleApp4
{
    class Program
    {
        public static void Main(string[] args)
        {
            var cashSuper = CashFactory.CreateCashSuper("8折");
            cashSuper.AcceptCash(900d);
        }
    }

    public abstract class CashSuper
    {
        public abstract double AcceptCash(double money);
    }

    public class CashNormal : CashSuper
    {
        public override double AcceptCash(double money)
        {
            return money;
        }
    }

   public class CashRebate : CashSuper
    {
        private double rebate;

        public CashRebate(double rebate)
        {
            this.rebate = rebate;
        }

        public override double AcceptCash(double money)
        {
            return money * rebate;
        }
    }

    public class CashReturn : CashSuper
    {
        private double moneyCondition;
        private double moneyReturn;
        public CashReturn(double condition,double @return)
        {
            moneyCondition = condition;
            moneyReturn = @return;
        }
        public override double AcceptCash(double money)
        {
            if (money >= moneyCondition)
            {
                return money - ((money / moneyCondition) * moneyReturn);
            }
            else
            {
                return money;
            }
        }
    }

    public class CashFactory
    {
        public static CashSuper CreateCashSuper(string type)
        {
            switch (type)
            {
                case "满300减50":return new CashReturn(300d, 50d);
                case "8折":return new CashRebate(0.8d);
                default:return new CashNormal();
            }
        }
    }   
}