 Creational design patterns abstract the instantiation process.  make a system independent of how its objects are created, composed, and represented. Main goal is: Provide an interface for creating families of related or dependent objects without specifying their concrete classes.

AbstractFactory (WidgetFactory) declares an interface for operations that create abstract product objects. ConcreteFactory (Motif & PMWidgetFactory) implements the operations to create concrete product objects.

AbstractProduct (Window, ScrollBar) declares an interface for a type of product object. ConcreteProduct (MotifWindow, MotifScrollBar) 1- defines a product object to be created by the corresponding concrete factory. 2-implements the AbstractProduct interface. Client uses only the interfaces declared by AbstractFactory and AbstractProduct

 a system should be independent of how its products are created.  a system should be configured with one of multiple families of products.  a family of related product objects is designed to be used together, and you need to enforce this constraint.  you want to provide a class library of products, and you want to reveal just their interfaces, not their implementations.

 It isolates concrete classes. ◦ It isolates clients from implementation classes. Clients manipulate instances through their abstract interfaces.  It makes exchanging product families easy. ◦ It can use different product configurations simple by changing the concrete factory.

 It promotes consistency among products ◦ To enforce that an application use objects from only one family at a time.  Supporting new kinds of products is difficult  Adding a new product requires extending the abstract interface which implies that all of its derived concrete classes also must change.  Essentially everything must change to support and use the new product family  abstract factory interface is extended  derived concrete factories must implement the extensions  a new abstract product class is added  a new product implementation is added  client has to be extended to use the new product

 Abstract Factory pattern to creating mazes class MazeFactory { public: MazeFactory(); virtual Maze * MakeMaze() const; virtual Wall * MakeWall() const; virtual Room * MakeRoom(int n) const; virtual Door* MakeDoor(Room *r1, Room* r2) const; }

 CreateMaze taking a MazeFactory as a parameter Maze *MazeGame::CreateMaze(MazeFactory& factory) { Maze * aMaze = factory.MakeMaze(); Room * r1 = factory.MakeRoom(1); Room *r2 = factory.MakeRoom(2); … }

 EnhantedMazeFactory class EnchantedMazeFactory: public MazeFactory { public: EnchantedMazeFactory(); virtual Room* MakeRoom(int n) const {return new EnchantedRoom(n, CastSpell());} virtual Door* MakeDoor(Room *r1, Room* r2) const {return new DoorNeedingSpell(r1,r2);} protected:Spell* CastSpell() const; }

 BombedMazeFactory Wall * BombedMazeFactory::MakeWall() const { return new BombedWall; } Room *BombedMazeFactory::MakeRoom(int n) const { return new RoomWithABomb(n); }

 Code using BombedMazeFactory MazeGame game; BombedMazeFactory factory; game.CreateMaze(factory);  CreateMaze can take an instance of EnchantedMazeFactory just as well to build enchanted mazes.

interface GUIFactory { public Button createButton(); } class WinFactory implements GUIFactory { public Button createButton() { return new WinButton(); } } class OSXFactory implements GUIFactory { public Button createButton() { return new OSXButton(); } }

interface Button { public void paint(); } class WinButton implements Button { public void paint() { System.out.println("I'm a WinButton"); } class OSXButton implements Button { public void paint() { System.out.println("I'm an OSXButton"); }

class Application { public Application(GUIFactory factory) { Button button = factory.createButton(); button.paint(); } public class ApplicationRunner { public static void main(String[] args) { new Application(createOsSpecificFactory()); } public static GUIFactory createOsSpecificFactory() { int sys = readFromConfigFile("OS_TYPE"); if (sys == 0) { return new WinFactory(); } else { return new OSXFactory(); } }