简单工厂模式

理论

简单工厂模式又叫静态方法模式（因为工厂类定义了一个静态方法）。现实生活中，工厂是负责生产产品的。同样在设计模式中，简单工厂模式我们可以理解为负责生产对象的一个类，称为“工厂类”。

作用：

将“类实例化的操作”与“使用对象的操作”分开，让使用者不用知道具体参数就可以实例化出所需要的类，从而避免了在客户端代码中显式指定，实现了解耦。

实例

用任意一种面向对象语言实现一个计算器控制台程序

UML类图

 实现代码

#include <iostream>
#include <string>
using namespace std;

class Operation
{
public:
	void GetNumber(double num1, double num2)
	{
		number_A = num1;
		number_B = num2;
	}

	virtual double GetResult() = 0;

protected:
	double number_A;
	double number_B;
};

class OperationAdd :public Operation 
{
public:
	double GetResult()
	{
		return number_A + number_B;
	}
};

class OperationSub :public Operation
{
public:
	double GetResult()
	{
		return number_A - number_B;
	}
};

class OperationMul :public Operation
{
public:
	double GetResult()
	{
		return number_A * number_B;
	}
};

class OperationDiv :public Operation
{
public:
	double GetResult()
	{
		if (number_B == 0)
		{
			cout << "除数不能为0" << endl;
			exit(0);
		}
		return number_A / number_B;
	}
};

//工厂类
class OperationFactory
{
public:
	static Operation* cerateOperate(char operate)
	{
		switch (operate) 
		{
		case('+'):
			return new OperationAdd;
		case('-'):
			return new OperationSub;
		case('*'):
			return new OperationMul;
		case('/'):
			return new OperationDiv;
		default:
			break;
		}
	}
};

void test()
{
	double num1, num2;
	char choice;
	cout << "请输入第一个数：" << endl;
	cin >> num1;
	cout << "您想进行的运算是：" << endl;
	cin >> choice;
	cout << "请输入第二个数：" << endl;
	cin >> num2;

	double result = 0;
	OperationFactory factory;
	Operation* operate = factory.cerateOperate(choice); //父类指针指向子类对象
	operate->GetNumber(num1, num2);
	result = operate->GetResult();
	cout << "num1 " << choice << " num2 = " << result << endl;

	delete operate;
}

int main()
{
	test();

	system("pause");
	return 0;
}