工廠方法模式

讓一個具體的類對應一個工廠。然後把所有工廠進行抽象。通過抽象工廠實現具體的工廠來創建對象。如果需要新增一個類，那麽就需要創建一個工廠類來創建對象

優點：

1. 符合開閉原則。是簡單工廠改進

2. 實現創建和使用分離

缺點：

1. 類的個數龐大。增加一個具體對象類就需要增加一個對應工廠類。增加維護成本

參考代碼：

class Fruit
{
public:
    virtual void showName() = 0;
};

class Apple : public Fruit
{
public:
    virtual void showName()
    {
        cout 
 
<< "I am apple." << endl;
    }
};
class Banana : public Fruit
{
public:
    virtual void showName()
    {
        cout << "I am banana." << endl;
    }
};
class Pear : public Fruit
{
public:
    virtual void showName()
    {
        cout << "I am pear." << endl;
    }
};

 
class FactoryMethod
{
public:
    virtual Fruit* createFruit() = 0;
};

class AppleFactory : public FactoryMethod
{
public:
    virtual Fruit* createFruit()
    {
        return new Apple();
    }
};
class BananaFactory : public FactoryMethod
{
public:
    virtual Fruit* createFruit()
    {
        return
 
 new Banana();
    }
};
class PearFactory : public FactoryMethod
{
public:
    virtual Fruit* createFruit()
    {
        return new Pear();
    }
};

int main()
{
    FactoryMethod* factory = new AppleFactory();
    Fruit* apple = factory->createFruit();
    apple->showName();
    delete factory;
    delete apple;
    return 0;
}

適用場景

1. 客戶端不知道它鎖需要對象的類

2. 抽象工廠類通過其子類來指定創建哪個對象

[Design Pattern] 抽象工廠模式