定義：

從設計模式的型別上來說，簡單工廠模式是屬於建立型模式，又叫做靜態工廠方法（StaticFactory Method）模式，但不屬於23種GOF設計模式之一。簡單工廠模式是由一個工廠物件決定創建出哪一種產品類的例項。簡單工廠模式是工廠模式家族中最簡單實用的模式，可以理解為是不同工廠模式的一個特殊實現。

場景：

我們要開一家比薩商店，定義了一個簡單的披薩工廠，可以根據客戶的需要製作芝士披薩、辣腸比薩、蛤蜊披薩、素食披薩。根據傳入的披薩型別從披薩工廠生產出客戶所需要的披薩。

類圖：

c++程式碼如下：

#include <iostream>
#include <string
 
>
#include <vector>
using namespace std;

class PizzaType
{
public:
    enum EPizzaType{cheese,pepperoni,clam,veggie};
};

class Pizza 
{
public:
    virtual ~Pizza() {};
    string getName();
    void prepare();
    void bake();
    void cut();
    void box();
protected:
    string name;
    string
 
 dough;
    string sauce;
    vector<string> toppings;
};

class CheesePizza : public Pizza 
{
public:
    CheesePizza();
};

class PepperoniPizza : public Pizza 
{
public:
    PepperoniPizza();
};

class ClamPizza : public Pizza
{
public:
    ClamPizza();
};

class VeggiePizza : public Pizza 
{
public
 
: 
    VeggiePizza();
};

class SimplePizzaFactory
{
public:
    Pizza* createPizza(PizzaType::EPizzaType type);
};

class PizzaStore 
{
private:
    SimplePizzaFactory factory;
public:
    Pizza* orderPizza(PizzaType::EPizzaType type);
};


string Pizza::getName() 
{
    return name;
}
void Pizza::prepare() 
{
    printf("Preparing %s\n",name.c_str());
}
void Pizza::bake() 
{
    printf("Baking %s\n",name.c_str());
}
void Pizza::cut() 
{
    printf("Cutting %s\n",name.c_str());
}
void Pizza::box() 
{
    printf("Boxing %s\n",name.c_str());
}

CheesePizza::CheesePizza()
{
    name = "Cheese Pizza";
    dough = "Regular Crust";
    sauce = "Marinara Pizza Sauce";
    toppings.push_back("Fresh Mozzarella");
    toppings.push_back("Parmesan");
}

PepperoniPizza::PepperoniPizza() 
{
    name = "Pepperoni Pizza";
    dough = "Crust";
    sauce = "Marinara sauce";
    toppings.push_back("Sliced Pepperoni");
    toppings.push_back("Sliced Onion");
    toppings.push_back("Grated parmesan cheese");
}

ClamPizza::ClamPizza() 
{
    name = "Clam Pizza";
    dough = "Thin crust";
    sauce = "White garlic sauce";
    toppings.push_back("Clams");
    toppings.push_back("Grated parmesan cheese");
}

VeggiePizza::VeggiePizza() 
{
    name = "Veggie Pizza";
    dough = "Crust";
    sauce = "Marinara sauce";
    toppings.push_back("Shredded mozzarella");
    toppings.push_back("Grated parmesan");
    toppings.push_back("Diced onion");
    toppings.push_back("Sliced mushrooms");
    toppings.push_back("Sliced red pepper");
    toppings.push_back("Sliced black olives");
}

Pizza* SimplePizzaFactory::createPizza(PizzaType::EPizzaType type) 
{
    Pizza* pizza = NULL;
    if (PizzaType::cheese == type) 
    {
        pizza = new CheesePizza();
    }
    else if (PizzaType::pepperoni == type) 
    {
        pizza = new PepperoniPizza();
    } 
    else if (PizzaType::clam == type) 
    {
        pizza = new ClamPizza();
    } 
    else if (PizzaType::veggie == type) 
    {
        pizza = new VeggiePizza();
    }
    return pizza;
}

Pizza* PizzaStore::orderPizza(PizzaType::EPizzaType type) 
{
    Pizza* pizza = NULL;
    pizza = factory.createPizza(type);
    pizza->prepare();
    pizza->bake();
    pizza->cut();
    pizza->box();
    return pizza;
}

int main()
{
    PizzaStore pizzaStore;
    Pizza* pCheesePizza = pizzaStore.orderPizza(PizzaType::cheese);
    Pizza* pPepperoniPizza = pizzaStore.orderPizza(PizzaType::pepperoni);
    Pizza* pClamPizza = pizzaStore.orderPizza(PizzaType::clam);
    Pizza* pVeggiePizza = pizzaStore.orderPizza(PizzaType::veggie);
    
    delete pCheesePizza;
    delete pPepperoniPizza;
    delete pClamPizza;
    delete pVeggiePizza;

    return 0;
}

執行後結果如下：

Preparing Cheese Pizza
Baking Cheese Pizza
Cutting Cheese Pizza
Boxing Cheese Pizza
Preparing Pepperoni Pizza
Baking Pepperoni Pizza
Cutting Pepperoni Pizza
Boxing Pepperoni Pizza
Preparing Clam Pizza
Baking Clam Pizza
Cutting Clam Pizza
Boxing Clam Pizza
Preparing Veggie Pizza
Baking Veggie Pizza
Cutting Veggie Pizza
Boxing Veggie Pizza

參考圖書：《Head First 設計模式》