小菜学设计模式 工厂设计模式 Simple Factory Pattern

设计模式的工厂设计模式。 工厂模式有以下几种形态：
简单工厂（Simple Factory）模式
工厂方法（Factory Method）模式
抽象工厂（Abstract Factory）模式
优点：
工厂类含有必要的判断逻辑，可以决定在什么时候创建哪一个产品类的实例，客户端可以免除直接创建产品对象的责任，而仅仅"消费"产品。简单工厂模式通过这种做法实现了对责任的分割。
缺点：
当产品有复杂的多层等级结构时，工厂类只有自己，以不变应万变，就是模式的缺点。因为工厂类集中了所有产品创建逻辑，一旦不能正常工作，整个系统都要受到影响。
同时，系统扩展困难，一旦添加新产品就不得不修改工厂逻辑，有可能造成工厂逻辑过于复杂。
另外，简单工厂模式通常使用静态工厂方法，这使得无法由子类继承，造成工厂角色无法形成基于继承的等级结构。以上描述来自：C#设计模式（4）－Simple Factory Pattern
 
前台调用时使用：

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 = "";

Operation oper;
oper = OperationFactory.createOperate(strOperate);
oper.NumberA = Convert.ToDouble(strNumberA);
oper.NumberB = Convert.ToDouble(strNumberB);
strResult = oper.GetResult().ToString();

Console.WriteLine("结果是：" + strResult);

Console.ReadLine();

}
catch (Exception ex)
{
Console.WriteLine("您的输入有错：" + ex.Message);
}
}
}

 

操作实体类Operation和运算类工厂：

using System;
using System.Collections.Generic;
using System.Text;

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

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

///
/// 数字B
///
public double NumberB
{
get
{
return _numberB;
}
set
{
_numberB = value;
}
}

///
/// 得到运算结果
///
///
public virtual double GetResult()
{
double result = 0;
return result;
}

///
/// 检查输入的字符串是否准确
///
///
///
///
public static string checkNumberInput(string currentNumber, string inputString)
{
string result = "";
if (inputString == ".")
{
if (currentNumber.IndexOf(".") < 0)
{
if (currentNumber.Length == 0)
result = "0" + inputString;
else
result = currentNumber + inputString;
}
}
else if (currentNumber == "0")
{
result = inputString;
}
else
{
result = currentNumber + inputString;
}

return result;
}

}

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

///
/// 减法类
///
class OperationSub : Operation
{
public override double GetResult()
{
double result = 0;
result = NumberA - NumberB;
return result;
}
}

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

///
/// 除法类
///
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;
}
}

///
/// 平方类
///
class OperationSqr : Operation
{
public override double GetResult()
{
double result = 0;
result = NumberB * NumberB;
return result;
}
}

///
/// 平方根类
///
class OperationSqrt : Operation
{
public override double GetResult()
{
double result = 0;
if (NumberB < 0)
throw new Exception("负数不能开平方根。");
result = Math.Sqrt(NumberB);
return result;
}
}

///
/// 相反数类
///
class OperationReverse : Operation
{
public override double GetResult()
{
double result = 0;
result = -NumberB;
return result;
}
}

///
/// 运算类工厂
///
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;
}
case "sqr":
{
oper = new OperationSqr();
break;
}
case "sqrt":
{
oper = new OperationSqrt();
break;
}
case "+/-":
{
oper = new OperationReverse();
break;
}
}

return oper;
}
}

}

类似的结构图。

参考学习：C#设计模式（4）－Simple Factory Pattern