设计模式之简单工厂

介绍：

从设计模式的类型上来说，简单工厂模式是属于创建型模式，又叫做静态工厂方法（StaticFactory Method）模式，但不属于23种GOF设计模式之一。简单工厂模式是由一个工厂对象决定创建出哪一种产品类的实例。简单工厂模式是工厂模式家族中最简单实用的模式，可以理解为是不同工厂模式的一个特殊实现。
UML图示：



代码实现：
class Operator
{
private:
	double m_numberA;
	double m_numberB;
public:
	virtual double GetResult();
	void SetNumberA(double a)
	{
		m_numberA = a;
	}
	void SetNumberB(double b)
	{
		m_numberB = b;
	}
};

class OperatorAdd : public Operator
{
public:
	double GetResult()
	{
		return m_numberA + m_numberB;
	}
};

class OperatorSub : public Operator
{
public:
	double GetResult()
	{
		return m_numberA - m_numberB;
	}
};

class OperatorMul : public Operator
{
public:
	double GetResult()
	{
		return m_numberA * m_numberB;
	}
};

class OperatorDiv : public Operator
{
public:
	double GetResult()
	{
		if (0 == m_numberB)
		{
			printf("除数不能为零!\n");
			return 0;
		}
		return m_numberA / m_numberB;
	}
};

class SimpleFactory
{
public:
	Operator* CreateOperator(char c)
	{
		Operator* oper = NULL;
		switch (c)
		{
		case '+':
			oper = new OperatorAdd();
			break;
		case '-':
			oper = new OperatorSub();
			break;
		case '*':
			oper = new OperatorMul();
			break;
		case '/':
			oper = new OperatorDiv();
			break;
		default:
			break;
		}
                return oper;
          }
};

int main()
{
	SimpleFactory factory;
	Operator* oper = NULL;
	oper = factory.CreateOperator('+');
	oper->SetNumberA(10.0);
	oper->SetNumberB(2.0);
	printf("result:%d\n", oper->GetResult());
	return 0;
}