C++设计模式3:工厂模式
工厂模式都是在那种有着大量类的程序里面使用的，比如我突然要产生许多的类，这时候就可以用工厂模式，工厂模式有如下三种类型。
简单工厂
用户输入实例化的信息(比如产品名称)，向工厂申请对象，工厂返回相应的对象，用户完全不需要知道，这个对象的具体构造方式，封装了对象的创建。
#include<iostream>
using namespace std;
class Car
{
public:Car() {}~Car() {}virtual void show() = 0;
};
class Audi:public Car
{
public:Audi() {}~Audi() {}void show(){cout << "this is Audi" << endl;}
};
class Baoma :public Car
{
public:Baoma() {}~Baoma() {}void show(){cout << "this is Baoma" << endl;}
};
enum CarType
{BAOMA,AUDI
};
class SimpleFactory
{
public:SimpleFactory() {}~SimpleFactory(){}Car* createCar(CarType type){switch (type){case BAOMA:return new Baoma();case AUDI:return new Audi();}}
};
int main()
{SimpleFactory factory;unique_ptr< Car>myaudi(factory.createCar(AUDI));unique_ptr< Car>mybaoma(factory.createCar(BAOMA));myaudi->show();mybaoma->show();return 0;
}
简单工厂存在明显的缺点，那就是如果要产生新的产品，就需要改变源头的工厂类，因为简单工厂只有一个工厂，这不符合软件设计的开闭原则。
工厂方法
实现能够产生不同产品的工厂，用这些工厂产生它们对应的产品，如果有新的产品，就添加工厂类就可以了，完全不用改变之前实现的工厂类。
#include<iostream>
using namespace std;
class Car
{
public:Car() {}~Car() {}virtual void show() = 0;
};
class Audi:public Car
{
public:Audi() {}~Audi() {}void show(){cout << "this is Audi" << endl;}
};
class Baoma :public Car
{
public:Baoma() {}~Baoma() {}void show(){cout << "this is Baoma" << endl;}
};
class FactoryMethod
{
public:virtual Car* createCar() = 0;
};
class AudiFactory:public FactoryMethod
{
public:Car* createCar(){return new Audi();}
};
class BaoMaFactory:public FactoryMethod
{
public:Car* createCar(){return new Baoma();}
};
int main()
{unique_ptr<FactoryMethod>audifactory(new AudiFactory());unique_ptr<FactoryMethod>baomafactory(new BaoMaFactory());unique_ptr< Car>myaudi(audifactory->createCar());unique_ptr< Car>mybaoma(baomafactory->createCar());myaudi->show();mybaoma->show();return 0;
}
抽象工厂
把有关联关系的，属于一个产品簇的所有产品创建的接口函数，放在一个抽象工厂里面，派生类应该负责创建该产品簇里面的所有产品，比如华为和小米都是派生类，抽象工厂要生产手机和耳机以及充电头，那么小米和华为这两个派生类工厂，就要产生这些产品。
显然，抽象工厂也有不好的地方，假如我华为要产生手机芯片这一新的产品，那么抽象工厂就要跟着改变，由于抽象工厂类是抽象的，所以所有派生类都要实现那个产生芯片的函数，不然派生类也会变成抽象类，但是小米不一定要自己生产芯片。
#include<iostream>
using namespace std;
class Car
{
public:Car() {}~Car() {}virtual void show() = 0;
};
class Audi:public Car
{
public:Audi() {}~Audi() {}void show(){cout << "this is Audi" << endl;}
};
class Baoma :public Car
{
public:Baoma() {}~Baoma() {}void show(){cout << "this is Baoma" << endl;}
};
class Light
{
public:Light() {}~Light() {}virtual void show() = 0;
};
class AudiLight:public Light
{
public:AudiLight() {}~AudiLight() {}void show(){cout << "this is AudiLight" << endl;}
};
class BaoMaLight :public Light
{
public:BaoMaLight() {}~BaoMaLight() {}void show(){cout << "this is BaoMaLight" << endl;}
};
class AbstractFactory
{
public:virtual Car* createCar() = 0;virtual Light* createLight() = 0;
};
class AudiFactory:public AbstractFactory
{
public:Car* createCar(){return new Audi();}Light* createLight(){return new AudiLight();}
};
class BaoMaFactory:public AbstractFactory
{
public:Car* createCar(){return new Baoma();}Light* createLight(){return new BaoMaLight();}
};
int main()
{unique_ptr<AbstractFactory>audifactory(new AudiFactory());unique_ptr<AbstractFactory>baomafactory(new BaoMaFactory());unique_ptr< Car>myaudi(audifactory->createCar());unique_ptr< Car>mybaoma(baomafactory->createCar());unique_ptr<Light>myaudilight(audifactory->createLight());unique_ptr<Light>mybaomalight(baomafactory->createLight());myaudi->show();myaudilight->show();mybaoma->show();mybaomalight->show();return 0;
}
显然，抽象工厂也有不好的地方，假如我华为要产生手机芯片这一新的产品，那么抽象工厂就要跟着改变，由于抽象工厂类是抽象的，所以所有派生类都要实现那个产生芯片的函数，不然派生类也会变成抽象类，但是小米不一定要自己生产芯片。