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static void Main(string[] args) { //面向过程的计算器 try { Console.WriteLine("请输入数字A: "); string strNumA = Console.ReadLine(); Console.WriteLine("请选择运算符号（+、-、*、/）: "); string strOperate = Console.ReadLine(); Console.WriteLine("请输入数字B: "); string strNumB = Console.ReadLine(); string strResult = string.Empty; switch (strOperate) { case "+": strResult = (Double.Parse(strNumA) + Double.Parse(strNumB)).ToString(); break; case "-": strResult = (Double.Parse(strNumA) - Double.Parse(strNumB)).ToString(); break; case "*": strResult = (Double.Parse(strNumA) * Double.Parse(strNumB)).ToString(); break; case "/": if (Double.Parse(strNumB) == 0) { throw new Exception("被除数不能为0！"); } strResult = (Double.Parse(strNumA) / Double.Parse(strNumB)).ToString(); break; default: throw new Exception("运算符输入错误！"); } Console.WriteLine(strNumA + " " + strOperate + " " + strNumB + " = " + strResult); } catch (Exception ex) { Console.WriteLine("您输入的有错：" + ex.Message); } Console.ReadKey(); }
思考：
上面的计算器是Console版的，如果我要实现WinForm版、Web版、手机版。那怎么办呢？
Ctrl-C, Ctrl-V是一种方法（我刚写代码的时候就是这么办的）。但是当重复的代码多了，维护起来，可能就是一场灾难。
这时面向对象的优势就体现出来了，把计算器的功能封装成一个计算器类，供Console, WinForm, Web等调用。将来要维护，只维护这一个类即可。
//业务的封装 - 计算 public class Operation { public static double CalcResult(double numA, double numB, string op) { double result = 0d; switch (op) { case "+": result = numA + numB; break; case "-": result = numA - numB; break; case "*": result = numA * numB; break; case "/": if (numB == 0) { throw new Exception("被除数不能为0！"); } result = numA / numB; break; default: throw new Exception("运算符输入错误！"); } return result; } } //客户端代码 - 界面 static void Main(string[] args) { try { Console.WriteLine("请输入数字A: "); string strNumA = Console.ReadLine(); Console.WriteLine("请选择运算符号（+、-、*、/）: "); string strOperate = Console.ReadLine(); Console.WriteLine("请输入数字B: "); string strNumB = Console.ReadLine(); string strResult = Operation.CalcResult(double.Parse(strNumA), double.Parse(strNumB), strOperate).ToString(); Console.WriteLine(strNumA + " " + strOperate + " " + strNumB + " = " + strResult); } catch (Exception ex) { Console.WriteLine("您输入的有错：" + ex.Message); } Console.ReadKey(); }
思考：
如果现在要加一个平方根运算，怎么办？看来只能改Operation类了，那么已经写好的加减乘除运算代码是不是也会暴露出来，面临着被误修改的风险（如果这个类是计算工资的类，那风险得多大）。而且添加完平方根后，整个类都要重新编译，岂不是很麻烦。
看来上面的实现扩展性和灵活性还是不够好，需要再设计一下。
/// <summary> /// 抽象类：运算类 /// </summary> public class Operation { private double _numA = 0; private double _numB = 0; public double NumA { get { return _numA; } set { _numA = value; } } public double NumB { get { return _numB; } set { _numB = value; } } public virtual double GetResult() { return 0; } } /// <summary> /// 加法 ： 继承运算类 /// </summary> public class OperationAdd : Operation { public override double GetResult() { return NumA + NumB; } } /// <summary> /// 减法 ： 继承运算类 /// </summary> public class OperationSub : Operation { public override double GetResult() { return NumA - NumB; } } /// <summary> /// 乘法 ： 继承运算类 /// </summary> public class OperationMul : Operation { public override double GetResult() { return NumA * NumB; } } /// <summary> /// 除法 ： 继承运算类 /// </summary> public class OperationDiv : Operation { public override double GetResult() { if (NumB == 0) throw new Exception("被除数不能为0"); else return NumA / NumB; } } /// <summary> /// 工厂 ： 生产计算器 /// </summary> public class OperationFactory { public static Operation createOperation(string op) { Operation oper = null; switch (op) { case "+": oper = new OperationAdd(); break; case "-": oper = new OperationSub(); break; case "*": oper = new OperationMul(); break; case "/": oper = new OperationDiv(); break; default: throw new Exception("操作符错误，只支持+-*/四则运算。"); } return oper; } } /// <summary> /// 客户端 /// </summary> /// <param name="args"></param> static void Main(string[] args) { try { Console.WriteLine("请输入数字A: "); string strNumA = Console.ReadLine(); Console.WriteLine("请选择运算符号（+、-、*、/）: "); string strOperate = Console.ReadLine(); Console.WriteLine("请输入数字B: "); string strNumB = Console.ReadLine(); Operation oper = OperationFactory.createOperation(strOperate); oper.NumA = double.Parse(strNumA); oper.NumB = double.Parse(strNumB); string strResult = oper.GetResult().ToString(); Console.WriteLine(strNumA + " " + strOperate + " " + strNumB + " = " + strResult); } catch (Exception ex) { Console.WriteLine("您输入的有错：" + ex.Message); } Console.ReadKey(); }
思考：
现在的计算器通过封装、继承、多态把程序的耦合度降低，更加的灵活，容易修改，易于服用。
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参考文献：《大话设计模式》第1章
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原文地址：http://www.cnblogs.com/chrisjjc/p/5077894.html
