Abstract Factory

Originally published 2016-02-15 · Boris Ivanov

1. Usage

When required to create family of related objects, and they should be easily changed to another family of related objects at run-time we use Abstract Factory;

2. UML class diagram

3. Pros

- related objects grouped together;
- easy switch at runtime between families of objects;
- making uniform way of working with classes regardless of implementation of concrete classes;

4. Cons

- Adding new product means changing Abstract Product and consequence changes in all derived classes;

5. Source code

# Source from https://sourcemaking.com
#define WINDOWS

class Widget {
public:
   virtual void draw() = 0;
};

class MotifButton : public Widget {
public:
   void draw() { cout << "MotifButton\n"; }
};
class MotifMenu : public Widget {
public:
   void draw() { cout << "MotifMenu\n"; }
};

class WindowsButton : public Widget {
public:
   void draw() { cout << "WindowsButton\n"; }
};
class WindowsMenu : public Widget {
public:
   void draw() { cout << "WindowsMenu\n"; } }; class Factory { public: virtual Widget* create_button() = 0; virtual Widget* create_menu() = 0; }; class MotifFactory : public Factory { public: Widget* create_button() { return new MotifButton; } Widget* create_menu() { return new MotifMenu; } }; class WindowsFactory : public Factory { public: Widget* create_button() { return new WindowsButton; } Widget* create_menu() { return new WindowsMenu; } }; Factory* factory; void display_window_one() { Widget* w&#091;&#093; = { factory->create_button(),
                   factory->create_menu() };
   w[0]->draw();  w[1]->draw();
}

void display_window_two() {
   Widget* w[] = { factory->create_menu(),
                   factory->create_button() };
   w[0]->draw();  w[1]->draw();
}

int main() {
#ifdef MOTIF
   factory = new MotifFactory;
#else // WINDOWS
   factory = new WindowsFactory;
#endif

   Widget* w = factory->create_button();
   w->draw();
   display_window_one();
   display_window_two();
}