(Factory Method) (Intent) (Motivation) (instantiate) (defer) f. (application) (application) ƒ (document) ¾ (application-specific)

Transcription

1 (Factory Method) (Intent) (instantiate)(defer) f y (Motivation) (Framework) g Ä k (application) ƒ (document) (application) (document) g (abstract) (clients) l ¾ (application-specific) f ¼ ¼ (DrawingApplication) (DrawingDocument), ¼ Â (application-specific) y y n y l y g g l ½ ½

2 n gÿ (CreateDocument operation) Ÿ m l y Ÿ (Applicability) s y s s ½l (localize) (Structure) (Participants) Product g ContreteProduct Product Creator m Product ƒ Creator m ContreteProduct Product ContreteCreator Œ(override) m ContreteProduct (Collaborations) Creator m ContreteProduct

3 (consequences) l (application-specific) w Product ContreteProduct ² ³ l Creator ¾ ContreteProduct s l Creator ¾ l ³(point of evolution) 1. (hooks) (hooks) Document Document CreateFileDialog kk (Product) ¾ g 2. Œ (parallel class hierarchies) Creator Œ Œ s Ÿ q} n Ÿ Ÿ k kh Ÿ (manipulator) xÿ Ÿ Ÿ Ÿ Œ

4 (Figure) CreateManipulator Ÿ (Manipulator)Œm Ÿ ƒ CreateManipulator m Ÿ ¾ l ŸŒ Œ f w Ÿ Ÿ  ½ Ÿ Âl (It localize knowledge of which classes belong together) (Implementation) 1. i. Creator g l ƒ ii. Creator ƒ ƒ Ÿ {k ŸŒ (The rule ensure that designers of subclass can change the class of objects their parent class instantiates if necessary) g x y 2. ƒƒ(multiple kinds) ƒ Product Document m CreateDocument ƒ Unidraw ƒ interface type TProductID = (MINE, YOURS, theirs); TProduct = class constructor Create; virtual;

5 TMyProduct = class(tproduct) TYourProduct = class(tproduct) TCreator = class constructor Create; virtual; // Create function CreateProduct(ProductID: TProductID): TProduct; virtual; implementation function TCreator.CreateProduct(ProductID: TProductID): TProduct; var aproduct: TProduct; aproduct:=nil; if ProductID = mine then aproduct := TMyProduct.Create; if ProductID = yours then aproduct := TYourProduct.Create; Result := aproduct; Œ Ÿ Creator nƒ n TCreator TmyCreator MyProduct YourProduct TProduct n TheirProduct 2000/12/08 type TMyCreator = class(tcreator)

6 // Create function CreateProduct(ProductID: TProductID): TProduct; override; TtheirProduct = class(tproduct) implementation function TMyCreator.CreateProduct(ProductID: TProductID): TProduct; var aproduct: TProduct; // Yours mine aproduct:=nil; if ProductID = mine then aproduct := TYourProduct.Create; if ProductID = yours then aproduct := TMyProduct.Create; if ProductID = theirs then aproduct := TtheirProduct.Create; if aproduct = nil then // acreator := Tcreator.Create; aproduct := acreator.createproduct(productid); Result := aproduct; TMyCreator.CreateProduct Yours Mine Theirs TMyCreator.CreateProduct 3. (language-specific) (caveats) Smalltalk m Creator ConcreteCreator ConcreteProduct C++ f (virtual method) (pure)f

7 Creator ConcreteProduct n Š product w Ÿ Ÿ n Product Creator Product 0 f Delphi nilÿ n product n product ¹ (lazy initialization) Š interface type TProduct = class constructor Create; virtual; TCreator = class constructor Create; virtual; function GetProduct(): TProduct; protected function CreateProduct(): TProduct;// private F_Product: TProduct; implementation constructor TCreator.Create; F_Product := nil; function TCreator.GetProduct(): TProduct; if F_Product = nil then acreator.create; F_Product := acreator.createproduct();

8 result := F_Product; function TCreator.CreateProduct(): TProduct; // 4. (templates) ¾ product l C++ ƒ Creator product À Delphi (Sample Code) CreateMaze m TMaze Œ (hard-codes) TMaze TRoom TDoor TWall Ÿ TMazeGame TMaze TRoom TDoor TWall TMazeGame = class(tmapsite) constructor Create; function CreateMaze: TMaze; // n // function makemaze(): Tmaze; virtual;abstract; function makeroom(n:integer): TRoom; virtual;abstract; function MakeWall(): TWall; virtual;abstract; function MakeDoor(r1,r2:TRoom): TDoor; virtual;abstract; m TMazeGame m TMaze TRoom TDoor TWall CreateMaze function TMazeGame.CreateMaze: TMaze; // n var amaze: TMaze;

9 r1, r2: Troom; adoor: TDoor; amaze := makemaze; r1 := makeroom(1); r2 := makeroom(2); adoor := MakeDoor(r1,r2); amaze.addroom(r1); amaze.addroom(r2); r1.setside(north,makewall()); r1.setside(east,adoor); r1.setside(south,makewall()); r1.setside(west,makewall()); r2.setside(north,makewall()); r2.setside(east,makewall()); r2.setside(south,makewall()); r2.setside(west,adoor); result:=amaze; x ¾ TMazeGame Œ TBombedMazeGame n k m k type TBombedMazeGame = class(tmazegame) function MakeWall(): TWall; override; function MakeRoom(n: integer): TRoom; override; implement function TBombedMazeGame.MakeWall(): TWall;

10 //m function TBombedMazeGame.MakeRoom(n: integer): TRoom; //m k TenchantedMazeGame n TEnchantedMazeGame = class(tmazegame) function MakeWall(): TWall; override; function MakeRoom(n: integer): TRoom; override; protected function CastSpell(): TSpell; function TEnchantedMazeGame.MakeWall(): TWall; //m Enchanted function TEnchantedMazeGame.MakeRoom(n: integer): TRoom; //m Enchanted k w (Known uses) (Related Patterns) g (Template Method) NewDocument (Prototype) ¾ Creator Product Ÿ (Initialize operation) Creator Initialize

11 Ÿ 2000/12/11