C++设计模式---工厂模式

 1 enum CTYPE{COREA,COREB};
 2 
 3 class SingleCore
 4 {
 5 public:
 6     virtual void show() = 0;
 7 };
 8 
 9 class SingleCoreA:public SingleCore
10 {
11 public:
12     void show(){ cout << "SingleCore A" << endl; }
13 };
14 
15 class SingleCoreB:public SingleCore
16 {
17 public:
18     void show(){ cout << "SingleCore B" << endl; }
19 };
20 
21 class Factory
22 {
23 public:
24     SingleCore* CreateSingleCore(enum CTYPE ctype)
25     {
26         if (COREA==ctype)
27             return new SingleCoreA();
28         else if (COREB==ctype)
29             return new SingleCoreB();
30         else
31             return nullptr;
32     }
33 };
34 
35 int main()
36 {
37     Factory factoryTemp;
38     SingleCore* core =     factoryTemp.CreateSingleCore(COREA);
39     core->show();
40     core = factoryTemp.CreateSingleCore(COREB);
41     core->show();
42     system("pause");
43     return 0;
44 
45 }
简单工厂模式的弊端是若向增加一种类型（比如B希望A生产Class3商品），则必须修改Factory类，不满足开放封闭原则。

工厂方法模式：是指定义一个用于创建对象的接口，让子类决定实例化哪一个类。Factory Method使一个类的实例化延迟到其子类；简单理解就是A公司开了两间工厂Factory1和Factory2分别生产商品1和商品2，商人B只需到对应工厂即可，而不需告诉A需要生产什么商品。
示例代码：

 1 class SingleCore
 2 {
 3 public:
 4     virtual void Show() = 0;
 5 };
 6 //单核A    
 7 class SingleCoreA : public SingleCore
 8 {
 9 public:
10     void Show() { cout << "SingleCore A" << endl; }
11 };
12 //单核B    
13 class SingleCoreB : public SingleCore
14 {
15 public:
16     void Show() { cout << "SingleCore B" << endl; }
17 };
18 class Factory
19 {
20 public:
21     virtual SingleCore* CreateSingleCore() = 0;
22 };
23 //生产A核的工厂    
24 class FactoryA : public Factory
25 {
26 public:
27     SingleCoreA* CreateSingleCore() { return new SingleCoreA(); }
28 };
29 //生产B核的工厂    
30 class FactoryB : public Factory
31 {
32 public:
33     SingleCoreB* CreateSingleCore() { return new SingleCoreB(); }
34 };
35 
36 int main()
37 {
38     FactoryA factoryA;              ///构建A工厂类
39     SingleCore* core = factoryA.CreateSingleCore();
40     core->Show();
41     FactoryB factoryB;
42     core = factoryB.CreateSingleCore();
43     core->Show();
44     system("pause");
45     return 0;
46 
47 }

工厂方法模式的缺点是需要为每个商品子类建立一个工厂子类

抽象工厂模式：为创建一组相关或者依赖的对象提供一个接口，且无需指定他们的具体类