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PrinciplesofSoftwareConstruction: Objects,Design,andConcurrencyPart2:DesigncasestudiesDesigncasestudy:JavaSwingCharlieGarrodChrisTimperley

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Administrivia

•  Readingduetoday:UMLandPatterns26.1and26.4•  Homework4bdueThursday,October17th

https://commons.wikimedia.org/wiki/File:1_carcassonne_aerial_2016.jpg

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KeyconceptsfromThursday

•  Observerdesignpattern•  Introductiontoconcurrency

–  Notenoughsynchronization:safetyfailure–  Toomuchsynchronization:livenessfailure

•  Event-basedprogramming•  IntroductiontoGUIs

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GUIprogrammingisinherentlymulti-threaded

•  Swingeventdispatchthread(EDT)handlesallGUIevents–  Mouseevents,keyboardevents,timerevents,etc.

•  Noothertime-consumingactivityallowedontheEDT–  Violatingthisrulecancauselivenessfailures

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Swinghasmanyeventlistenerinterfaces

•  ActionListener•  AdjustmentListener•  FocusListener•  ItemListener•  KeyListener

•  MouseListener•  TreeExpansionListener•  TextListener•  WindowListener•  …

classActionEvent{intwhen;StringactionCommand;intmodifiers;Objectsource();intid;…

}interfaceActionListener{voidactionPerformed(ActionEvente);

}

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Aside:lambdasvs.explicitclassdeclarations?

//staticpublicvoidmain…JFramewindow=…JPanelpanel=newJPanel();window.setContentPane(panel);JButtonbutton=newJButton(“Clickme”);button.addActionListener(newActionListener(){

publicvoidactionPerformed(ActionEvente){ System.out.println(“Buttonclicked”);}

});panel.add(button);window.setVisible(true);

panel to hold the button

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Aside:lambdasvs.explicitclassdeclarations?

//staticpublicvoidmain…JFramewindow=…JPanelpanel=newJPanel();window.setContentPane(panel);JButtonbutton=newJButton(“Clickme”);button.addActionListener((e)->{

System.out.println(“Buttonclicked");});panel.add(button);window.setVisible(true);

panel to hold the button

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Designdiscussion:DecouplingyourgamefromyourGUI

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Anarchitecturalpattern:Model-View-Controller(MVC)

Manageinputsfromuser:mouse,keyboard,etc.

Managedisplayofinformationonthescreen

Managedatarelatedtotheapplication

Model

View

Controller

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Today

•  Designcasestudy:GUIpotpourri–  Strategy–  Templatemethod–  Observer–  Composite–  Decorator–  Adapter–  Façade–  Command–  Chainofresponsibility

•  Anexerciseindesignpatterns

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Thedecoratorpatternabounds

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Thedecoratorpatternabounds

UMLfromhttps://medium.com/@dholnessii/structural-design-patterns-decorator-30f5a8c106a5

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Swinglayouts

see http://docs.oracle.com/javase/tutorial/uiswing/layout/visual.html

Thesimplest,anddefault,layout.Wrapsaroundwhenoutofspace.

LikeFlowLayout,butnowrapping

Moresophisticatedlayoutmanagers

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Anaïvehard-codedimplementation

•  AnewlayoutwouldrequirechangingoroverridingJPanel

classJPanel{protectedvoiddoLayout(){

switch(getLayoutType()){ caseBOX_LAYOUT:adjustSizeBox();break; caseBORDER_LAYOUT:adjustSizeBorder();break; ...}

}privateadjustSizeBox(){…}}

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Abettersolution:delegatethelayoutresponsibilities

•  Layoutclasses,e.g.:contentPane.setLayout(newFlowLayout());contentPane.setLayout(newGridLayout(4,2));

•  Similarly,thereareborderclassestodrawtheborders,e.g.:contentPane.setBorder(newEmptyBorder(5,5,5,5));

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AnotherGUIdesignchallenge:nestingcontainers

•  AJFramecontainsaJPanel,whichcontainsaJPanel(and/orotherwidgets),whichcontainsaJPanel(and/orotherwidgets),whichcontains…

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Thecompositepattern

•  Problem:Collectionofobjectshasbehaviorsimilartotheindividualobjects

•  Solution:Havecollectionofobjectsandindividualobjectsimplementthesameinterface

•  Consequences:–  Clientcodecantreatcollectionasifitwereanindividualobject–  Easiertoaddnewobjecttypes–  Designmightbecometoogeneral,interfaceinsufficientlyuseful

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Recall:Creatingabutton

//staticpublicvoidmain…JFramewindow=…JPanelpanel=newJPanel();window.setContentPane(panel);JButtonbutton=newJButton(“Clickme”);button.addActionListener((e)->{

System.out.println(“Buttonclicked");});panel.add(button);window.setVisible(true);

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Analternativebutton

classMyButtonextendsJButton{publicMyButton(){super(“Clickme”);}@OverrideprotectedvoidfireActionPerformed(ActionEvente){

super.fireActionPerformed(e);System.out.println(“Buttonclicked”);

}}//staticpublicvoidmain…JFramewindow=…JPanelpanel=newJPanel();window.setContentPane(panel);panel.add(newMyButton());window.setVisible(true);

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Designdiscussion:Strategyvs.templatemethodpatterns

//staticpublicvoidmain…JFramewindow=…JPanelpanel=newJPanel();window.setContentPane(panel);JButtonbutton=newJButton(“Clickme”);button.addActionListener((e)->{

System.out.println(“Buttonclicked");});panel.add(button);window.setVisible(true);

classMyButtonextendsJButton{publicMyButton(){super(“Clickme”);}@OverrideprotectedvoidfireActionPerformed(ActionEvente){

super.fireActionPerformed(e);System.out.println(“Buttonclicked”);

}}…

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Betteruseoftemplatemethod:partialcustomization

JComponent:

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Eventpropagationanddeepcontainerhierarchies

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Eventpropagationanddeepcontainerhierarchies

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Eventpropagationanddeepcontainerhierarchies

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Eventpropagationanddeepcontainerhierarchies

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Eventpropagationanddeepcontainerhierarchies

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Thechainofresponsibilitypattern

•  Problem:Youneedtoassociatefunctionalitywithinadeepnestedoriterativestructure,possiblywithmultipleobjects

•  Solution:Requestforfunctionality,passrequestalongchainuntilsomecomponenthandlesit

•  Consequences:–  Decouplessenderfromreceiverofrequest–  Cansimplifyrequest-handlingbyhandlingrequestsnearrootofhierarchy–  Handlingofrequestnotguaranteed

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ThedesignofJListandJTree

•  Highlyflexiblerenderingoflistsandtrees–  Canchangerenderingofcells–  Canchangesourceofdatatodisplay

//exampleofsimpleuseString[]items={“a”,“b”,“c”};JList<String>list=newJList<>(items);

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UsingJListswithaListModel

•  Allowsalistwidget(theview)toreacttochangesinthemodel

//withaListModelListModel<String>model=newDefaultListModel<>();model.addElement(“a”);JList<String>list=newJList<>(model);

interfaceListModel<T>{intgetSize();TgetElementAt(intindex);voidaddListDataListener(ListDataListenerl);voidremoveListDataListener(ListDataListenerl);

}

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UsingJListswithaListModel

•  Allowsalistwidget(theview)toreacttochangesinthemodel

//withaListModelListModel<String>model=newDefaultListModel<>();model.addElement(“a”);JList<String>list=newJList<>(model);

interfaceListModel<T>{intgetSize();TgetElementAt(intindex);voidaddListDataListener(ListDataListenerl);voidremoveListDataListener(ListDataListenerl);

}

interfaceListDataListenerextendsEventListener{voidintervalAdded(…);voidintervalRemoved(…);voidcontentsChanged(…);

}

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AttachingadatasourcetoaJList

•  Assumewehaveananagramgenerator,andwewanttoupdateaJListwithnewanagramsastheyaregenerated

//design1classAnagramGenimplementsListModel<String>{

List<String>items…

intgetSize(){returnitems.size();}StringgetElementAt(intindex){ items.get(index).toString();}voidaddListDataListener(ListDataListenerl){…}…

}

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AttachingadatasourcetoaJList

•  Assumewehaveananagramgenerator,andwewanttoupdateaJListwithnewanagramsastheyaregenerated

//design2classAnagramGen{

DefaultListModel<String>items…

publicListModel<String>getListModel(){ returnitems;}publicIterable<String>getItems(){ returnitems.elements();}…

}

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AttachingadatasourcetoaJList

•  Assumewehaveananagramgenerator,andwewanttoupdateaJListwithnewanagramsastheyaregenerated

//design3classAnagramAdapterimplementsListModel<String>{

privatefinalAnagramGenan;publicAnagramAdapter(AnagramGens){an=s;}

intgetSize(){returncount(an.getWords());}StringgetElementAt(intindex){ find(an.getWords(),index).toString();}voidaddListDataListener(ListDataListenerl){…}…

}

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Comparingthethreeproposeddesigns

+getItems()-items

AnagramGen

JList

+getSize()+getElementAt()

AnagramAdapter

+getSize()+getElementAt()

«interface»ListModel

+getItems()

AnagramGen

JList

+getSize()+getElementAt()

DefaultListModel

11

+getItems()+getSize()+getElementAt()

-items

AnagramGen

JList

+getSize()+getElementAt()

«interface»ListModel

1

2

3

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Theadapterpattern

•  Problem:YouhaveaclientthatexpectsoneAPIforaserviceprovider,andaserviceproviderwithadifferentAPI

•  Solution:WriteaclassthatimplementstheexpectedAPI,convertingcallstotheserviceprovider'sactualAPI

•  Consequences:–  Easyinteroperabilityofunrelatedclientsandlibraries

•  Clientcanuseunforeseenfuturelibraries–  Adapterclassiscoupledtoconcreteserviceprovider,canmakeitharder

tooverrideserviceproviderbehavior

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Theadapterpattern,illustrated

Havethis andthis? Usethis!

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Aside:Thefaçadepattern

Façade

√√

√

√

√

√ √

Subsystem classes

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Thefaçadevs.adapterpatterns

•  Motivation:–  Façade:ProvidesimpleinterfaceforacomplexAPI

•  Façadeinterfaceistypicallynew–  Adapter:MatchinterfaceexpectedbyanexistingclienttoexistingAPI

•  Adapterinterfaceisdefinedbytheexistingclient'sexpectations

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Today

•  Designcasestudy:GUIpotpourri–  Strategy–  Templatemethod–  Observer–  Composite–  Decorator–  Adapter–  Façade–  Command–  Chainofresponsibility

•  Anexerciseindesignpatterns

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Designpatternswehaveseensofar

Composite

Templatemethod

Strategy

Command

Iterator

Chainofresponsibility

Decorator

Adapter

Façade

Model-View-Controller

Observer

Factorymethod

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Designpatternswehaveseensofar

Composite

Templatemethod

Strategy

Command

Iterator

Chainofresponsibility

Decorator

Adapter

Façade

Model-View-Controller

Observer

Factorymethod

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Anoteondesign

•  Thepreviousexerciseisbackward–  "Here'sadesignpattern.Nowuseit."

•  Therealexercise:"HowdoIdesignthisprogramtoaccomplishmygoals?"–  "Aha!I'veseenthisproblembefore!"

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Nexttime

•  DesigncasestudyofJavaCollections

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Paperslidesfromlecturearescannedbelow..