The Abstract Factory pattern looks like the factories we ve
seen previously, but with several Factory Methods. Each of the Factory Methods
creates a different kind of object. When you create the factory object, you
decide how all the objects created by that factory will be used. The example in
GoF implements portability across various graphical user interfaces (GUIs): you
create a factory object appropriate to the GUI that you re working with, and
from then on when you ask it for a menu, a button, a slider, and so on, it will
automatically create the appropriate version of that item for the GUI. Thus,
you re able to isolate, in one place, the effect of changing from one GUI to
another.
As another example, suppose you are creating a
general-purpose gaming environment and you want to be able to support different
types of games. Here s how it might look using an Abstract Factory:
//: C10:AbstractFactory.cpp
// A gaming environment.
#include <iostream>
using namespace std;
class Obstacle {
public:
virtual void action() = 0;
};
class Player {
public:
virtual void interactWith(Obstacle*) = 0;
};
class Kitty: public Player {
virtual void interactWith(Obstacle* ob) {
cout << "Kitty has encountered a ";
ob->action();
}
};
class KungFuGuy: public Player {
virtual void interactWith(Obstacle* ob) {
cout << "KungFuGuy now battles against a
";
ob->action();
}
};
class Puzzle: public Obstacle {
public:
void action() { cout << "Puzzle"
<< endl; }
};
class NastyWeapon: public Obstacle {
public:
void action() { cout << "NastyWeapon"
<< endl; }
};
// The abstract factory:
class GameElementFactory {
public:
virtual Player* makePlayer() = 0;
virtual Obstacle* makeObstacle() = 0;
};
// Concrete factories:
class KittiesAndPuzzles : public GameElementFactory {
public:
virtual Player* makePlayer() { return new Kitty; }
virtual Obstacle* makeObstacle() { return new Puzzle;
}
};
class KillAndDismember : public GameElementFactory {
public:
virtual Player* makePlayer() { return new KungFuGuy;
}
virtual Obstacle* makeObstacle() {
return new NastyWeapon;
}
};
class GameEnvironment {
GameElementFactory* gef;
Player* p;
Obstacle* ob;
public:
GameEnvironment(GameElementFactory* factory)
: gef(factory), p(factory->makePlayer()),
ob(factory->makeObstacle()) {}
void play() { p->interactWith(ob); }
~GameEnvironment() {
delete p;
delete ob;
delete gef;
}
};
int main() {
GameEnvironment
g1(new KittiesAndPuzzles),
g2(new KillAndDismember);
g1.play();
g2.play();
}
/* Output:
Kitty has encountered a Puzzle
KungFuGuy now battles against a
NastyWeapon */ ///:~