【笔记】大话设计模式-1简单工厂模式

• 【笔记】大话设计模式-1简单工厂模式
• • 1 简介
  • 2 代码
  • • 2.1 定义基类
    • 2.2 创建派生类对象，这里以加减乘除为例
    • 2.3 创建工厂
    • 2.4 调用工厂函数

说白了，就是考虑用一个单独的类来做创造实例的过程，这就是工厂。

工厂就是实例化出合适的对象，通过多态，返回基类的方式。

举个例子，我想买一双鞋，一般情况下，我要去各个品牌店去买对应的鞋子，太麻烦了，现在，我直接去一家工厂，告诉工厂我要一双"王五"牌鞋子，工厂就直接给你了，这就是工厂方便的地方。将你所需要的实例直接给你。

好处：将来新增派生类的时候，对外提供的接口函数可以保持不变，只需新增派生类，并改变工厂的入参即可。

创建一个操作的基类，操作两个数，得到一个结果

// 基类
class Operation
{
public:
	Operation() {};
	~Operation() {};
	inline double GetNumberA()
	{
		return numberA;
	}

	inline void SetNumberA(double a)
	{
		numberA = a;
	}

	inline double GetNumberB()
	{
		return numberB;
	}

	inline void SetNumberB(double b)
	{
		numberB = b;
	}

	virtual double GetResult()
	{
		double result = 0.0;
		return result;
	}

private:
	double numberA{ 0.0 };
	double numberB{ 0.0 };
};

// 加法
class OperationAdd : public Operation
{
	double GetResult() override;	
};

double OperationAdd::GetResult()
{
	double result = GetNumberA() + GetNumberB();
	return result;
};

// 减法
class OperationSub : public Operation
{
	double GetResult() override;
};

double OperationSub::GetResult()
{
	double result = GetNumberA() - GetNumberB();
	return result;
}

// 乘法
class OperationMul : public Operation
{
	double GetResult() override;
};

double OperationMul::GetResult()
{
	double result = GetNumberA() * GetNumberB();
	return result;
}

// 除法
class OperationDiv : public Operation
{
	double GetResult() override;
};

double OperationDiv::GetResult()
{
	if (fabs(GetNumberB() - 0.0) < 1e-10) {
		std::cout << "The divisor can not be 0!" << std::endl;
		return 0.0;
	}
	double result = GetNumberA() / GetNumberB();
	return result;
}

// ========= 工厂函数 =========
class OperationFactory
{
public:
	OperationFactory();
	~OperationFactory();
	Operation* CreateOperate(char operate);
	void DeleteOperate();
private:
	Operation* oper;
};

OperationFactory::OperationFactory()
{
	oper = nullptr;
}

OperationFactory::~OperationFactory()
{
}


Operation* OperationFactory::CreateOperate(char operate)
{
	switch (operate)
	{
	case '+':
		oper = new OperationAdd();
		break;
	case '-':
		oper = new OperationSub();
		break;
	case '*':
		oper = new OperationMul();
		break;
	case '/':
		oper = new OperationDiv();
		break;
	default:
		oper = new OperationAdd();
		break;
	}
	return oper;
}

void OperationFactory::DeleteOperate()
{
	if (oper != nullptr){
		delete oper;
	}
}

int main()
{
	OperationFactory factory;
	Operation* oper = factory.CreateOperate('*');
	oper->SetNumberA(3.0);
	oper->SetNumberB(4.0);
	double res = oper->GetResult();
    std::cout << "result: " << res << std::endl;
	factory.DeleteOperate();
	return 0;
}

以上。