C#设计模式之：简单工厂

请用C#面向对象语言实现一个计算器控制台程序，要求输入两个数和运算符号，得到结果。

面向过程：

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

namespace PatternTest
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.Write("请输入数字A: ");
            string A = Console.ReadLine();

            Console.Write("请选择运算符号(+、-、*、/)：");
            string B = Console.ReadLine();

            Console.Write("请输入数字B: ");
            string C = Console.ReadLine();

            string D = "";
            if (B == "+")
                D = Convert.ToString(Convert.ToDouble(A) + Convert.ToDouble(C));
            if (B == "-")
                D = Convert.ToString(Convert.ToDouble(A) - Convert.ToDouble(C));
            if (B == "*")
                D = Convert.ToString(Convert.ToDouble(A) * Convert.ToDouble(C));
            if (B == "/")
                D = Convert.ToString(Convert.ToDouble(A) / Convert.ToDouble(C));

            Console.WriteLine("结果是: " + D);
        }
    }
}

测试结果

请输入数字A: 1
请选择运算符号(+、-、*、/)：+
请输入数字B: 2
结果是: 3
请按任意键继续. . .

缺陷:

1 对象命名不规范
2 没有判断除数不能为0的情况
3 面向过程, if 判断分支会多做无效判断

简单工厂

类图

代码

// Operation.cs
namespace PatternTest.SampleFactory
{
    public class Operation
    {
        private double _numberA = 0;
        private double _numberB = 0;

        public double NumberA { get => _numberA; set => _numberA = value; }
        public double NumberB { get => _numberB; set => _numberB = value; }

        public virtual double GetResult()
        {
            double result = 0;
            return result;
        }
    }
}

// OperationAdd.cs
namespace PatternTest.SampleFactory
{
    class OperationAdd : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA + NumberB;
            return result;
        }
    }
}

// OperationSub.cs
namespace PatternTest.SampleFactory
{
    class OperationSub : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA - NumberB;
            return result;
        }
    }
}

// OperationMul.cs
namespace PatternTest.SampleFactory
{
    class OperationMul : Operation
    {
        public override double GetResult()
        {
            double result = 0;
            result = NumberA * NumberB;
            return result;
        }
    }
}

// OperationDiv.cs
namespace PatternTest.SampleFactory
{
    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;
        }
    }
}

// OperationFactory.cs
namespace PatternTest.SampleFactory
{
    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;
        }
    }
}

// test
namespace PatternTest.SampleFactory
{
    class Program
    {
        Operation oper;
        oper = OperationFactory.createOperate("+");
        oper.NumberA = 1;
        oper.NumberB = 2;
        double result = oper.GetResult();
        Console.WriteLine("结果是: " + result);
    }
}

优点:

如果有一天要修改加法运算,只要修改OperationAdd 即可
如果有一天要添加新的复杂运算,只要添加相应的运算子类,然后在运算类工厂的switch分支中增加其分支