一、简单工厂模式 ： 面向对象 特性 封装

计算器实例

（利用面向对象封装的特性，将业务的逻辑与界面的逻辑分开，降低耦合度）

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net;
using System.Net.Sockets;


namespace Test
{
    //运算类（）
    public class Operation
    {
        public static double GetResult(double numberA, double numberB, string operate)
        {
            double result = 0d;
            switch (operate)
            {
                case "+":
                    result = numberA + numberB;
                    break;
                case "-":
                    result = numberA - numberB;
                    break;
                case "*":
                    result = numberA * numberB;
                    break;
                case "/":
                    result = numberA / numberB;
                    break;
                default:
                    break;
            }
            return result;
        }
    }

    public class Program
    {
        static void Main(string[] args)
        {
            try
            {
                Console.Write("请输入数字A：");
                string strNumberA = Console.ReadLine();
                Console.Write("请选择运算符号（+ 、- 、*、/、）：");
                string strOperate = Console.ReadLine();
                Console.Write("请输入数字B：");
                string strNumberB = Console.ReadLine();
                string strResult = "";
                strResult = Convert.ToString(Operation.GetResult(Convert.ToDouble(strNumberA),
                    Convert.ToDouble(strNumberB), strOperate));
                Console.WriteLine("结果是：" + strResult);
                Console.ReadLine();
            }
            catch (Exception ex)
            {
                Console.WriteLine("您输入的有错：" + ex.Message);
            }
        }
    }
}

///////////////////////紧耦合 vs 松耦合

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Net;
using System.Net.Sockets;


namespace Test
{
    //运算类
    public class Operation
    {
        private double _numberA = 0;
        private double _numberB = 0;

        public double NumberA
        {
            get { return _numberA;}
            set { _numberA = value; }
        }

        public double NumberB
        {
            get { return _numberB; }
            set { _numberB = value; }
        }
        public virtual double GetResult()
        {
            double result = 0;
            return result;
        }
    }
    
    //加减乘除类
    class OperationAdd:Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA + NumberB;
            return result;
        }
    }
    //减法
    class OperationSub : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA - NumberB;
            return result;
        } 
    }

    //乘法
    class OperationMul : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA * NumberB;
            return result;
        }
    }

    //除法
    class OperationDiv : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            if (NumberB == 0)
                throw new Exception("除数不能为0");
            result = NumberA / NumberB;
            return result;
        }
    }
    //简单工厂
    public class OperationFactory
    {
        public static Operation createOperate(string operate)
        {
            Operation oper = null;
            switch (operate)
            {
                case "+":
                    oper = new OperationAdd();
                    break;
                case "-":
                    oper = new OperationSub();
                    break;
                case "*":
                    oper = new OperationMul();
                    break;
                case "/":
                    oper = new OperationDiv();
                    break;
            }
            return oper;
        }
    }

    public class Program
    {
        static void Main(string[] args)
        {
            Console.Write("请选择运算符号（+ 、- 、*、/、）：");
            string strOperate = Console.ReadLine();
            Operation oper;
            oper = OperationFactory.createOperate(strOperate);
            Console.Write("请输入数字A：");
            oper.NumberA = Convert.ToDouble(Console.ReadLine());
            Console.Write("请输入数字B：");
            oper.NumberB = Convert.ToDouble(Console.ReadLine());
            double result = oper.GetResult();
            Console.WriteLine("结果是：" + result);
            Console.ReadLine();
        }
    }
}