The Adapter Pattern

SE-2811Dr. Mark L. Hornick

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Scenario: An Existing System (your client code) interfaces to a Vendor Class library you purchased and incorporated into an application your company is currently selling

Existing System

Vendor1 Class

The Vendor goes out of business; what do you do???

Vendor1 interface

The original configuration

SE-2811Dr. Mark L. Hornick

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The ClientApp is writtensuch that it is heavily dependenton the functionality implementedin ServiceProvider, and is loadedwith calls to various ServiceProvidermethods.

ServiceProvider may implementnumerous methods in a real situation;not only the few methods shown here

Adapter (Wrapper) Pattern

Existing System

Vendor2 Class

Vendor2 Class

Existing System

Adapter

Adapter• Implements the

interface your classes expect

• And talks to the vendor interface to service your requests.

The Adapter configuration

1. The original ServiceProvider class is obsolete and discarded

2. An interface declaring the same methodsas the original ServiceProvider is created

3. A replacement classfor the originalServiceProvider is found that providessimilar functionality,but with a differentset of methods: the adaptee

4. An adapter class is writtenwhich maps calls from the original methods to the new methods

The Adapter Pattern features The client makes a request to the adapter by calling a

method on it by continuing to program to the interface that mimics the methods of the original class.

The adapter translates the request into one or more calls on the adaptee The amount of code is usually small, but may be complex due

to indirect mappings from the original methods to the new methods.

The adapter transforms data or results from the adaptee into the form expected by the client The client receives the results of the call and doesn’t care that

there is an adapter doing the translation. The only change to the client is that it must create an instance

of the adapter rather than the original vendor class.

Cases to use Adapter

Legacy code exists that interfaces to a class library that has changed Revision change Vendor change

New application is being developed that will have to interface to a class library that has yet to be defined Define an interface and write the adapter later

SE-2811Dr. Mark L. Hornick

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The Façade Pattern

SE-2811Dr. Mark L. Hornick

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Watching a Movie...

Use multiple interfaces (remotes) to Turn on Receiver/amplifier Turn on TV/Monitor Turn on DVD player Set the Receiver input to DVD Put the Monitor in HDMI input mode Set the Receiver volume to medium Set Receiver to DTS Surround Start the DVD player.

Interacting with the following classes:• Receiver/Amplifier• TV/Monitor• DVD

To decrease the complexity..

We can create a new class TheaterFacade (e.g. a universal remote) which exposes a few methods such as watchMovie().

The façade treats the various components as a sub system and calls on them to implement the watchMovie method.

So to watch a movie, we just call one method, watchMovie and it communicates with the Monitor, DVD, and Receiver for us.

The façade still leaves the subsystem accessible to be used directly. If you need the advanced functionality of the subsystem classes, they are available for use.

The Problem

Complex system Consisting of multiple

subsystems Each with its own interface,

each with many methods

Difficult for clients (blue) to deal with

Facade Solution

Solution Centralize subsystem

interface Simplify/reduce number of

centralized methods Façade presents new

unified “face” to clients Facade

Removing the burden from beginning Java developers with a Façade (WinPlotter)

SE-2811Dr. Mark L. Hornick

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class winPlotter

DrawingWindow

- currentPenColor: java.awt.Color- items: java.util.ArrayList- contentPane: java.awt.Container- showGrid: boolean- backgroundColor: java.awt.Color- xinc: int- yinc: int- gridColor: java.awt.Color- drawPanel: DrawPanel

+ DrawingWindow()+ setWindowSize(x :int, y :int) : void+ erase() : void+ setWindowTitle(title :String) : void+ setPenColor(c :Color) : void+ setBackgroundColor(backgroundColor :Color) : void+ drawLineTo(x :int, y :int) : void+ moveTo(x :int, y :int) : void+ drawPointAt(x :int, y :int) : void+ textAt(x :int, y :int, text :String) : void+ setGrid(showGrid :boolean, xinc :int, yinc :int, gridColor :Color) : void+ paint(gr :Graphics) : void

DrawPanel

# paintComponent(g :Graphics) : void+ doPaint(gr :Graphics) : void

DrawItem

+ MOVE: int = 0 {readOnly}+ DRAW: int = 1 {readOnly}+ POINT: int = 2 {readOnly}+ TEXT: int = 3 {readOnly}+ opCode: int+ x: int = 0+ y: int = 0+ text: String+ color: Color

+ DrawItem(x :int, y :int, opCode :int, color :Color)+ DrawItem(x :int, y :int, opCode :int, color :Color, text :String)

FrameWindowConstants

AccessibleRootPaneContainer

TransferHandler.HasGetTransferHandler

swing::JFrame

+ EXIT_ON_CLOSE: int = 3 {readOnly}- defaultLookAndFeelDecoratedKey: Object = new StringBuffe... {readOnly}- defaultCloseOperation: int = HIDE_ON_CLOSE- transferHandler: TransferHandler# rootPane: JRootPane# rootPaneCheckingEnabled: boolean = false# accessibleContext: AccessibleContext = null

+ JFrame()+ JFrame(gc :GraphicsConfiguration)+ JFrame(title :String)+ JFrame(title :String, gc :GraphicsConfiguration)# frameInit() : void# createRootPane() : JRootPane# processWindowEvent(e :WindowEvent) : void+ setDefaultCloseOperation(operation :int) : void+ getDefaultCloseOperation() : int+ setTransferHandler(newHandler :TransferHandler) : void+ getTransferHandler() : TransferHandler+ update(g :Graphics) : void+ setJMenuBar(menubar :JMenuBar) : void+ getJMenuBar() : JMenuBar# isRootPaneCheckingEnabled() : boolean# setRootPaneCheckingEnabled(enabled :boolean) : void# addImpl(comp :Component, constraints :Object, index :int) : void+ remove(comp :Component) : void+ setLayout(manager :LayoutManager) : void+ getRootPane() : JRootPane# setRootPane(root :JRootPane) : void+ setIconImage(image :Image) : void+ getContentPane() : Container+ setContentPane(contentPane :Container) : void+ getLayeredPane() : JLayeredPane+ setLayeredPane(layeredPane :JLayeredPane) : void+ getGlassPane() : Component+ setGlassPane(glassPane :Component) : void+ getGraphics() : Graphics+ repaint(time :long, x :int, y :int, width :int, height :int) : void+ setDefaultLookAndFeelDecorated(defaultLookAndFeelDecorated :boolean) : void+ isDefaultLookAndFeelDecorated() : boolean# paramString() : String+ getAccessibleContext() : AccessibleContext

JComponentAccessible

swing::JPanel

- uiClassID: String = "PanelUI" {readOnly}

+ JPanel(layout :LayoutManager, isDoubleBuffered :boolean)+ JPanel(layout :LayoutManager)+ JPanel(isDoubleBuffered :boolean)+ JPanel()+ updateUI() : void+ getUI() : PanelUI+ setUI(ui :PanelUI) : void+ getUIClassID() : String- writeObject(s :ObjectOutputStream) : void# paramString() : String+ getAccessibleContext() : AccessibleContext

::Lab1App

«facade»WinPlotter

- window: DrawingWindow- width: int- height: int- xmin: int- ymin: int- xmax: int- ymax: int- xscale: float- yscale: float- showGrid: boolean

+ WinPlotter()- logicalToPixel(xlog :int, ylog :int) : Point+ drawTo(x :int, y :int) : void+ erase() : void+ moveTo(x :int, y :int) : void+ drawPoint(x :int, y :int) : void+ printAt(x :int, y :int, text :String) : void+ setBackgroundColor(red :int, green :int, blue :int) : void+ setPenColor(red :int, green :int, blue :int) : void+ setWindowSize(width :int, height :int) : boolean+ setPlotBoundaries(xmin :int, ymin :int, xmax :int, ymax :int) : boolean+ setGrid(showGrid :boolean, xinc :int, yinc :int, gridColor :Color) : boolean+ setWindowTitle(title :String) : void

+items

*

-drawPanel

-window

Generic Pattern

SE-2811Dr. Mark L. Hornick

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Facade Consequences

Shields clients from subsystem components Make subsystem easier to use

Reduces coupling from client to subsystem classes Allow internal classes to change freely Permit “layering” of system function Level of client-subsystem coupling

Make Facade an abstract class Different concrete subclasses for different implementations of

the subsystem. Configure the façade object with different subsystem

objects.

SE-2811Dr. Mark L. Hornick

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Facade Applications

Interface to existing library Unify or “clean up” complex interface

Design layered system Various service levels Façade abstracts interface of each level

Provide abstract interfaces To alternative implementations