Design Patterns II

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Design Patterns (II)

• Shyh-Kang Jeng
• Department of Electrical Engineering
• National Taiwan University

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Creating Mazes
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Creating Mazes

• Maze MazeGameCreateMaze( )
• Maze aMaze new Maze
• Room r1 new Room(1)
• Room r2 new Room(2)
• Door theDoor new Door(
• r1, r2 )
• aMaze-gtAddRoom( r1 )
• aMaze-gtAddRoom( r2 )
• Set sides for each room
• return aMaze

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Builder Pattern

• Separate the construction of a complex object
  from its representation so that the same
  construction process can create different
  representations
• The algorithm for creating a complex object
  should be independent of the parts that make up
  the object and how they are assembled
• Gives finer control over the construction process

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Builder Pattern
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Builder Pattern
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Class MazeBuilder

• class MazeBuilder
• public
• virtual void BuildMaze( )
• virtual void BuildRoom( int room )
• virtual void BuildDoor(
• int roomFrom, int roomTo )
• virtual Maze GetMaze( )
• return NULL
• protected
• MazeBuilder( )

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Method CreateMaze

• Maze MazeGameCreateMaze(
• MazeBuilder builder )
• builder.BuildMaze( )
• builder.BuildRoom(1)
• builder.BuildRoom(2)
• builder.BuildDoor(1, 2)
• return builder.GetMaze( )

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Class StandardMazeBuilder

• class StandardMazeBuilder
• public MazeBuilder
• public
• StandardMazeBuilder( )
• virtual void BuildMaze( )
• virtual void BuildRoom(
• int room )
• virtual void BuildDoor(
• int roomFrom, int roomTo )
• virtual Maze GetMaze( )
• private
• Maze currentMaze

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Class CountingMazeBuilder

• class CountingMazeBuilder
• public MazeBuilder
• public
• CountingMazeBuilder( )
• virtual void BuildMaze( )
• virtual void BuildRoom(
• int room )
• virtual void BuildDoor(
• int roomFrom, int roomTo )
• virtual Maze GetCounts( )
• private
• int doors, rooms

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Method BuildRoom

• CountingMazeBuilder
• CountingMazeBuilder()
• rooms 0
• doors 0
• void CountingMazeBuilderBuildRoom(
• int )
• rooms

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Invoking MazeBuilder

• Maze maze
• MazeGame game
• StandardMazeBuilder builder1
• game.CreateMaze( builder1 )
• maze builder1.GetMaze()
• int rooms, doors
• CountingMazeBuilder builder2
• game.CreateMaze( builder2 )
• builder2.GetCounts( rooms, doors )

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Singleton Pattern

• Ensure a class only has one instance, and provide
  a global point of access to it
• Provide controlled access to sole instance
• Reduce name space

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Singleton Pattern
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Class MazeFactory

• class MazeFactory
• public
• static MazeFactory Instance( )
• protected
• MazeFactory( )
• private
• static MazeFactory instance

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Invoking Singleton Instance

• MazeFactory
• MazeFactoryinstance NULL
• MazeFactory MazeFactoryInstance( )
• if( instance NULL )
• instance new MazeFactory
• return instance

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Subclass of a Singleton

• class BombedMazeFactory
• public MazeFactory

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Invoking Singleton Instance

• MazeFactory MazeFactoryInstance( )
• if( instance ! NULL )
• const char mazeStyle
• getenv(MAZESTYLE)
• if(strcmp(mazeStyle,bombed)0)
• instance new BomedMazeFactory
• else if
• else
• instance new MazeFactory
• return instance

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Class Singleton

• class Singleton
• public
• static void Register( char name,
• Singleton)
• static Singleton Instance()
• protected
• static Singleton Lookup(
• const char name)
• private
• static Singleton instance
• static ListltNameSingletonPairgt registry

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Method Instance

• Singleton SingletonInstance()
• if( instance NULL )
• const char singletonName
• getenv(SINGLETON)
• instance
• Lookup( singletonName )
• return instance

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Register a Singleton Object

• class MySingleton public Singleton
• Static MySingleton theSingleton
• MySingletonMySingleton()
• SingletonRegister(MySingleton,
• this)

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Drawing Editor
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Adapter Pattern

• Convert the interface of a class into another
  interface clients expect
• Allow classes work together that could not
  otherwise because of incompatible interfaces
• Clients call operations on an Adapter instance.
  In turn, the adapter calls Adaptee operations
  that carry out the request

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Adapter Pattern
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Class Shape

• class Shape
• public
• Shape( )
• virtual void BoundingBox (
• Point bottomLeft,
• Point topRight ) const
• virtual Manipulator CreateManipulator( )
  const

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Class TextView

• class TextView
• public
• TextView( )
• void GetOrigin(Coord x, Coord y) const
• void GetExtent(Coord width,
• Coord height) const
• virtual bool IsEmpty( ) const

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Class TextShape

• class TextShape public Shape
• public
• TextShape(TextView)
• virtual void BoundingBox(
• Point bottomLeft,
• Point topRight ) const
• virtual bool IsEmpty( ) const
• virtual Manipulator CreateManipulator( )
  const
• private
• TextView text

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Method BoundingBox

• void TextShapeBoundingBox(
• Point bottomLeft,
• Point topRight ) const
• Coord bottom, left, width, height
• text-gtGetOrigin(bottom, left)
• text-gtGetExtent(width, height)
• bottomLeft Point(bottom, left)
• topRight Point(bottomheight, leftwidth)

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Compiler System
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Façade Pattern

• Provide a unified interface to a set of
  interfaces in a subsystem
• Define a higher-level interface that makes the
  subsystems easier to use
• Not prevent applications from using subsystem
  classes if we need to
• Can choose between ease of use and generality

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Façade Pattern
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Class Compiler

• class Compiler
• public
• Compiler( )
• virtual void Compile(
• istream, BytecodeStream)

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Method Compile

• void CompilerCompile(
• istream input,
• BytecodeStream output)
• Scanner scanner(input)
• ProgramNodeBuilder builder
• Parser parser
• parser.parse(scanner, builder)
• RISCCodeGenerator generator(output)
• ProgramNode parseTree builder.GetRootNode(
  )
• parseTree-gtTraverse(generator)

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Graphics
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Proxy Pattern

• Provide a surrogate or placeholder for another
  object to control access to it
• Forward requests to real subject when
  appropriate, depending on the kind of proxy
• Remote proxy can hide the fact that an object
  resides in a different address space
• Virtual proxy can perform optimizations such as
  creating an object on demand

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Proxy Pattern
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Class Graphic

• class Graphic
• public
• virtual Graphic( )
• virtual void Draw( ) 0
• virtual void HandleMouse(
• Event event)0
• virtual
• const Point GetExtent( ) 0
• virtual void Load(istream from) 0
• virtual void Save(ostream to)
• 0
• protected
• Graphic( )

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Class Image

• class Image public Graphic
• public
• Image(string file)
• virtual Image( )
• virtual void Draw(
• const Point at)
• virtual void HandleMouse(
• Event event)
• virtual const Point GetExtent( )
• virtual void Load(istream from)
• virtual void Save(ostream to)

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Class ImageProxy

• class ImageProxy public Graphic
• public
• ImageProxy(string file)
• virtual ImageProxy( )
• protected
• Image GetImage( )
• private
• Image image
• Point extent
• string fileName

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Method GetImage

• ImageProxyImageProxy(
• string fileName)
• fileName fileName
• extent PointZero
• image NULL
• Image ImageProxyGetImage( )
• if( image NULL )
• image new Image(fileName)
• return image

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Methods in ImageProxy

• void ImageProxyDraw(
• const Point at)
• GetImage( )-gtDraw(at)
• void ImageProxyHandleMouse(
• Event event ) GetImage( )
• -gtHandleMouse(event)
• void ImageProxySave(ostream to)
• to ltlt extent ltlt fileName
• void ImageProxyLoad(
• ifstream from)
• from gtgt extent gtgt fileName

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Invoking ImageProxy

• class TextDocument
• public
• TextDocument( )
• Void Insert(Graphic)
• TextDocument text
• new TextDocument
• Text-gtInsert( new ImageProxy(anImageFileName))

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Font Dialog Box
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Mediator Pattern

• Define an object that encapsulates how a set of
  objects interact
• Promote loose coupling by keeping objects from
  referring to each other explicitly
• Let the client vary interactions of objects
  independently
• Centralize control

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Mediator Pattern
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Mediator Pattern
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Mediator Pattern
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Class DialogDirector

• class DialogDirector
• public
• virtual DialogDirector( )
• virtual void ShowDialog( )
• virtual void WidgetChanged(Widget) 0
• protected
• DialogDirector( )
• virtual void CreateWidgets( ) 0

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Class Widget

• class Widget
• public
• Widget(DialogDirector)
• virtual void Changed( )
• virtual void HandleMouse(
• MouseEvent event)
• private
• DialogDirector director

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Class ListBox

• class ListBox public Widget
• public
• ListBox(DialogDirector)
• virtual string GetSelection( )
• virtual void SetList(
• Listltstringgt listItems)
• virtual void HandleMouse(
• MouseEvent event)

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Class FontDialogDirector

• class FontDialogDirector
• public DialogDirector
• public
• FontDialogDirector( )
• virtual FontDialogDirector( )
• virtual void WidgetChanged(Widget)
• protected
• virtual void CreateWidgets( )
• private
• ListBox fontList

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Presentations of Data
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Observer Pattern

• Define a one-to-many dependency between objects
  so that when one object changes state, all its
  dependents are notified and updated automatically

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Observer Pattern
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Observer Pattern
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Class Observer

• class Subject
• class Observer
• public
• virtual Observer( )
• virtual void Update(
• Subject theChangedSubject) 0
• protected
• Observer( )

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Class Subject

• class Subject
• public
• virtual Subject( )
• virtual void Attach(Observer)
• virtual void Detach(Observer)
• virtual void Notify( )
• protected
• Subject( )
• private
• ListltObservergt observers

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Methods in Subject

• void SubjectAttach(Observer o)
• observers-gtAppend(o)
• void SubjectNotify( )
• ListIteratorltObservergt i(observers)
• for(i.First( ) !i.IsDone( ) i.Next( ))
• i.CurrentItem( )-gtUpdate(this)

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TCP Connection
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State Pattern

• Allow an object to alter its behavior when its
  internal state changes
• Localize state-specific behavior and partition
  behavior for different states
• Make state transitions explicit
• State objects can be shared

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State Pattern
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Class TCPConnection

• class TCPState
• class TCPConnection
• public
• TCPConnection( )
• void ActiveOpen( )
• private
• friend class TCPState
• void ChangeState(TCPState)
• private
• TCPState state

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Class TCPState

• class TCPState
• public
• virtual void ActiveOpen(TCPConnection)
• virtual void Synchronize(TCPConnection)
• virtual void Acknowledge(TCPConnection)
• virtual void Send(TCPConnection)
• protected
• void ChangeState(
• TCPConnection,TCPState)

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State Classes

• class TCPListen public TCPState
• public
• static TCPState Instance( )
• virtual void Send(TCPConnection)
• class TCPClosed public TCPState
• public
• static TCPState Instance( )
• virtual void ActiveOpen(TCPConnection)

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Document-Application Application Framework
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Template Method Pattern

• Define the skeleton of an algorithm in an
  operation, deferring some steps to subclasses
• Let subclasses redefine certain steps of an
  algorithm without changing the algorithms
  structure
• Hook operations

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Template Method Pattern
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Methods in View

• void ViewDisplay( )
• SetFocus( )
• DoDisplay( )
• ResetFocus( )
• void ViewDoDisplay( )
• void MyViewDoDisplay( )