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FreeWebinars,Videos,andLiveTrainingMr.Jonesplanstohavefreestep-by-stepdemonstrationwebinars,videos,andlivetrainingswalkingpeoplethroughconceptsofSeleniumandQTP/UFTfromA-Z.Thematerialwillteach/trainindividualsthefundamentalsoftheprogramminglanguage,fundamentalsofSeleniumandQTP/UFT,andimportantconceptsofSeleniumandQTP/UFT.Allofthewebinars,videos,andlivetrainingwillbedirectedtowardbeginnersaswellasmid-levelautomationengineers.

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TableofContentsFREEWEBINARS,VIDEOS,ANDLIVETRAINING

REXJONES’CONTACTINFORMATION

TABLEOFCONTENTS

PREFACE

ABOUTTHEAUTHOR

COPYRIGHT,LEGALNOTICE,ANDDISCLAIMER

ACKNOWLEDGEMENTS

CHAPTER1INTRODUCTIONTOOBJECT-ORIENTEDPROGRAMMING

CLASSES,OBJECTS,ANDMETHODS

ARRAYSANDSTRINGS

INHERITANCE

PACKAGES

INTERFACES

ERRORS,EXCEPTIONS,ANDDEBUGGING

UTILIZINGINPUTANDOUTPUT

CHAPTER2CLASSES,OBJECTS,ANDMETHODS

CLASSES

OBJECTS

METHODS

THISKEYWORD

ANNOTATIONS

ACCESSMODIFIERS

STATICKEYWORD

CHAPTER3ARRAYSANDSTRINGS

SINGLE-DIMENSIONALARRAYS

MULTI-DIMENSIONALARRAYS

FOR-EACHLOOP

STRINGS

CHAPTER4INHERITANCE

FUNDAMENTALSOFINHERITANCE

SUPERCLASSOBJECT

INHERITINGPRIVATEMEMBERS

SUPERCLASSANDSUBCLASSCONSTRUCTORS

POLYMORPHISM

ABSTRACTION

KEYWORDFINAL

CHAPTER5PACKAGES

CREATEAPACKAGE

IMPORTAPACKAGE

JAVACLASSLIBRARY

CHAPTER6INTERFACES

INTERFACEIMPLEMENTATION

INTERFACEVARIABLES

MULTIPLEINHERITANCE

DEFAULTINTERFACEMETHOD

CHAPTER7ERRORS,EXCEPTIONS,ANDDEBUGGING

ERRORTYPES

THROWABLEEXCEPTIONPARENTCLASS

JAVA’SBUILT-INEXCEPTIONS

COMMONEXCEPTIONS

PRINCIPLESOFHANDLINGEXCEPTIONS

TRY/CATCHBLOCK

FINALLYBLOCK

CATCHATHROWABLEEXCEPTION

METHODSDEFINEDBYTHROWABLE

THROWVSTHROWS

DEBUGGING

CHAPTER8UTILIZINGINPUTANDOUTPUT

STREAMS

FILEINPUT/OUTPUT

CONCLUSION

RESOURCES

BOOKSBYREXJONESII

SIGNUPTORECEIVE

PrefaceAccordingtoTIOBE,Javaisthemostpopularprogramminglanguagewithintheprogrammingcommunity.ThereforeJavaisagreatlanguagetolearnintheworldofautomatingapplications.AcoresetofJavaisnecessarytobeeffectiveonautomationprojects.Part2–Java4SeleniumWebDriverprovidesacoresetofJavaplusconceptsinvolvinginheritance,packages,andmuchmore.

TargetAudience

Thetargetaudienceisprogrammerswithknowledgeofvariables,datatypes,operators,branches,andloops.ItisrecommendedtoreadPart1–Java4SeleniumWebDriver,ifanindividualneedstogainafoundationinJava.

Purpose

Thepurposeofthisbookistonotoverwhelmyouwithhundredsandhundredsofpages(knownasinformationoverload)regardingJava.Howeveritwillprovidevaluableinformationthatisconcisewithstraightforwarddefinitions,examples,andfigures.AfterreadingPart2–Java4SeleniumWebDriver,athoroughunderstandingofJavaandobject-orientedprogrammingwillbeinyourpossession.

http://www.tiobe.com/tiobe_index

AbouttheAuthor

RexAllenJonesIIisaQA/SoftwareTesterwithapassionforsharingknowledgeabouttestingsoftware.Hehasbeenwatchingwebinars,attendingseminars,andtestingapplicationssinceFebruary2005.Mr.JonesgraduatedfromDeVryUniversityinJune1999withaBachelor’sofSciencedegreeinComputerInformationSystems(CIS).

Currently,RexisaSr.ConsultantandformerBoardofDirectorforUserGroup:Dallas/FortWorthMercuryUserGroup(DFWMUG)andmemberofUserGroup:Dallas/FortWorthQualityAssuranceAssociation(DFWQAA).InadditiontohisUserGroupmemberships,heisaCertifiedSoftwareTesterEngineer(CSTE)andhasaTestManagementApproach(TMap)certification.

Mr.Jones’adviceforpeopleinterestedinFunctionalAutomationTestingistolearntheprogramminglanguage.Thisadviceledhimtowritebooksfourprogrammingbooks“(Part1&Part2)YouMustLearnVBScriptforQTP/UFT”and“(Part1&Part2)Java4SeleniumWebDriver”.VBScriptistheprogramminglanguageforUnifiedFunctionalTesting(UFT)formerlyknownasQuickTestProfessional(QTP)andJavaisoneoftheprogramminglanguagesforSeleniumWebDriver.

Copyright,LegalNotice,andDisclaimerThispublicationisprotectedundertheUSCopyrightActof1976.Allrightsarereservedincludingresalerightswhichappliestointernational,federal,state,andlocallaws.Thepurchaserisnotallowedtoshareorsellthisbooktoanyone.

Pleasenotethatmuchofthispublicationisbasedonpersonalexperienceandanecdotalevidence.Theauthorhasmadeeveryreasonableattempttoproduceaccuratecontentinthisbook.Heassumesnoresponsibilityforunknownerrorsoromissions.Therefore,thepurchasershouldusethisinformationashe/sheseesfit.

Anytrademarks,servicemarks,productnamesornamedfeaturesareassumedtobethepropertyoftheirrespectiveownersandusedonlyforreference.

Copyright©2016Test4Success,LLC.Allrightsreservedworldwide.

AcknowledgementsIwouldliketoexpressmygratitudetomywifeTiffany,childrenOliviaRexe’andRexIII,editorSamanthaMann,family,friends,andthemanypeoplewhoprovidedencouragement.Writingthisbooktooktimeandyoursupporthelpedpushedthisbookforward.

ThankYou,

RexAllenJonesII

Chapter1IntroductiontoObject-Oriented

ProgrammingObject-OrientedProgramming(OOP)isthemostpopularparadigminprogramming.Itisanapproachtoprogrammingthatcentersaroundobjects.Asaresult,identifyingobjectsisoneofthemostessentialprinciplesinOOP.Accordingtodictionary.com,anobjectisanythingvisibleortangible.Thereforeobjectscanbeaperson,place,orthingwherebyitisrecognizedinprogrammingliketherealworld.Allobjectshavetwocharacteristics:stateandbehavior.Stateidentifiestheobjectandbehaviorrepresenttheactionsoftheobject.

Chapter1underlinesobject-orientedprogramming(OOP)byprovidinganoverviewofthisbook“Part2–Java4SeleniumWebDriver”:

Classes,Objects,andMethods

ArraysandStrings

Inheritance

Packages

Interfaces

Errors,Exceptions,andDebugging

UtilizingInputandOutput

http://www.dictionary.com/browse/object?s=t

Classes,Objects,andMethodsJavaisanobject-orientedprogramming(OOP)languagecontainingclasses,objects,andmethods(seeClasses,Objects,andMethodsinChapter2).Aclassisablueprintforcreatinganobjectandamethodexecuteajobfortheobject.Classesincludedataandcodethatoperateonthedata.ObjectsserveasthefoundationforOOPwhilemethodsperformactions.Amethod’sresponsibilityistoinstructtheprogramwhatactiontoperformandhowtoperformtheaction.

ArraysandStringsInJava,arraysandstringsareobjects(seeArraysandStringsinChapter3).Anarrayisagroupofrelatedvariableswiththesamedatatype,samename,andfixednumberofvalues.Allitemsinthearrayareaccessedbyanindexwhichstartsatzero.Ontheotherhand,astringisagroupofunchangeablecharacters.Manymethodsareavailableforstringsthatfacilitateanoperationontheobject.

InheritanceInheritanceisahierarchicalconceptwhichallowscodeandobjectstobereused(seeInheritanceinChapter4).Eachclassallowsotherclassestoinherititscode.Asaresult,therelationshipbetweentheclassesaresuperclassandsubclass.Superclassistheparentclassandsubclassisthechildclass.Theclassesmaintainacertainamountdataincommonwhileholdinguniquecharacteristics.

PackagesApackageisacollectionofrelatedclasses(seePackagesinChapter5).Thepackageiscomparabletoafolderandtheclassesaresimilartofileswithinthefolder.Eachclasswithinthepackagecanbeaccessedbythepackagename.Itisimportanttoknowthatapackagemustbeimportedifaclasswantstousemembersfromadifferentclass.

InterfacesAninterfaceisacollectionofrelatedmethods(seeInterfacesinChapter6).Generally,mostinterfacesdonotincludethebodyofamethod.Thereforeaninterfacemethodrevealswhatactiontoperformbutnothowtoperformtheaction.Thisconceptallowsaclasstoimplementtheinterfacemethodanddecidehowtoperformtheaction.Eachclasshastheabilitytoimplementadifferentactionforthesameinterfacemethod.

Errors,Exceptions,andDebuggingErrorsareunavoidableproblemsinaprogram.Newprogrammersaswellasexperiencedprogrammerswillfaceerrors.Syntax,runtime,andlogicalarethreetypesoferrorsinJava.Syntaxerrorsstopthecodefromexecutingwhileruntimeerrorsallowcodetoexecutethengenerateanerror.Logicalerrorsarethemostdifficulterrorstodetectduetonoerrormessageduringexecution.Theprogrammermustknowwhattoexpectinordertofindandresolvealogicalerror.

Anexceptionisanerrorthatisoccursatruntime.Thistypeoferrorcanbemanagedbyablockofcodecalledanexceptionhandler.Exceptionhandlersallowtheprogramtogenerateanerrorbutcontinueexecutingaftertheerror.Debuggingisaprocessthatallowsaprogrammertoobservethencorrectanerrorand/orexception.Atoolcalleddebuggersimplifiesthetaskofresolvingerrorsduetobreakpointsanditsstep-by-stepfeatures.

Note:SeeErrors,Exceptions,andDebugginginChapter7formoreinformation

UtilizingInputandOutputJava’sInputandOutput(I/O)isaverylargesystemconsistingofmanyclasses,interfaces,andmethods(seeUtilizingInputandOutputinChapter8).Informationisreadfromaninputsourceandwrittentoanoutputdestination.Theprogramsperforminputandoutputthroughstreamswherebystreamsrepresentdata.FilesinJavaarestoredandorganizedforconvenience.Mostofthefilesarestructuredinahierarchyknownasatree.Atthetopofeverytreeistherootnodewhichcontainsfoldersandfiles.Allfoldersandfileshaveadistinctivepathwithinthetree.Thefilescanbecreated,deleted,moved,copied,andverifiedforexistence.

Chapter1providedanoverviewoftheupcomingchapters.Thesubsequentchaptersexploreclasses,objects,methods,arrays,strings,inheritance,packages,interfaces,errors,exceptions,debugging,andJava’sinput/outputsystem.Chapter2willthoroughlyexplainclasses,objects,andmethodswhichisthecornerstoneofobject-orientedprogramming.

Chapter2Classes,Objects,andMethods

Object-orientedprogramming(OOP)isaprogramminglanguagestructuredaroundobjects.Classes,objects,andmethodsareinterrelatedfundamentalswithinOOP.Anobjectisanythingthatcanbeseenorperceived.However,aclassisatemplateforobjectswhileamethodsprovideinteractionwithaclassfromvariouscomponentsoftheprogram.

Thedataandthecode(knownasstatements)thatoperateonthedataaretwomergednotionsofanobject.Asaresult,thetwomergednotionsallowaconceptcalledinformationhidingwherebydatacanbehidden.Thereforebydefaultanobject’sdatacanbeaccessedonlybymethodsholdingtheobject.Thelimitedaccesspreventotherprogramcomponentsfrominterferingandcausingerrors.Ifanothercomponentwantstochangeanobject’sdatathenthecomponentmustcallapubliclyaccessiblemethod.Thefollowingarefourtypesofmethods:

1. Instance–Amethodthatcanbeaccessedbyobjects2. Class–Amethodsharedbetweenallobjectsinaclass3. Main–Aspecialmethodusedtorunanapplication.Thistypeofmethodisnot

neededforSeleniumWebDriver.4. Constructor–Aspecialmethodusedtoinitializeobjectsofaparticularclass

Methodsandvariablesarelabeledmembersofaclasssincetheyformtheclass.Accesstobothmembersarecontrolledbyfourmodifiers:

1. public–Amodifierthatallowsaccesstocodedefinedoutsideofitsclass2. private–Amodifierthatallowsaccesstoothermemberswithinitsclass3. nomodifier–Amodifierthatallowsaccesstoallclasseswithinitspackage4. protected–Amodifierthatallowsaccesswithinitspackageandtoallsubclasses

Usually,membersofaclassareaccessedbyobjectswithinitsownclass.However,thekeyword“static”permitsamembertobeaccessedbeforeanyobjectiscreatedwithinitsclass.Methodsandvariablesaredeclaredstaticwhenthekeywordisplacedinfrontofthemember.

Chaptertwowillexplainthefollowingregardingclasses,objects,andmethods:

Classes

Objects

Methods

ThisKeyword

Annotations

AccessModifiers

StaticKeyword

ClassesClassesdefinedataandcodethatoperatesonthedata.Thedataisrepresentedbyvariableswhilethecodeisrepresentedbymethods.Bothvariablesandmethodsaremembersofaclass.Henceaclassisatemplatethatdefinesthestructureofanobject.Thereforethestructureofaclassmustbeprecise.Classesformedwithonelogicalentitymakestheclasscomplete.Itisimportanttodefineclasseswithinformationthatislogicallyconnected.Forexample,aclassthatcontainsinformationaboutanEnglishclasswouldnotcontainunrelatedinformationabouttheschoolzonespeedlimit.

Mostreal-worldclassesincludeaninstancevariableandamethodtooperateontheinstancevariable.Rememberfromthefirstbook“(Part1)AbsoluteBeginner:Java4SeleniumWebDriver”aninstancevariableisdeclaredinsideaclassbutoutsideofamethod.Asaresult,valuesofaninstancevariableareuniquetoeachobject.Thistypeofvariablecanbeusedbeforeorafteritisinitializedwithvisibilitytoallmethodswithinaclass.Thefollowingisthesyntaxfordefiningaclass:

SyntaxclassClassName

{

//DeclareInstanceVariable

variableTypevariableName1;


variableTypevariableNameN;

//DeclareMethods

methodTypemethodName1()

{

//BodyoftheMethod

}

methodTypemethodName2()

{

//BodyoftheMethod

}

methodTypemethodNameN()

{

//BodyoftheMethod

}

}

ThefollowingisanexampleofadataonlyclasscalledEnglishwhichstoresthreeinstancevariables:students,weeks,anddays.

classEnglish

{

intstudents;

intweeks;

intdays;

}

Figure2.1–DataOnlyClass

Line1definestheEnglishclassandlines3–5declaretheinstancevariables.Englishisaschoolcoursewhileinstancevariablestudentsrepresentthenumberofstudentsintheclass,weeksrepresentthenumberofweeksfortheEnglishcourse,anddaysrepresentthenumberofdaysperweek.Wheneveraclassisdefined,itisconsideredanewdatatype.Inthiscase,thenewdatatype“English”istheclassname.

Note:AconventionfornamingclassesistouseanUpperCamelCasewhereeachwordintheclassnamebeginswithacapitalletter(i.e.,EnglishCourse).

ObjectsObject-Orientedprogramming(OOP)isbuiltuponobjects.Thereforeitiscrucialtounderstandhowobjectsareformedandutilized.Anobjectcanbeanything.Allobjectssharetwocharacteristics:stateandbehavior.Stateidentifiestheobjectandbehaviorrepresenttheactionsoftheobject.Forexample,adoghasastate(name,breed,color)whichidentifiesthedogandbehavior(bark,jump,fetch)whichrepresentthedog’sactions.Thestateofanobjectissupportedbyvariableswhilebehaviorisimplementedthroughmethods.Objectsarecreatedusingthekeyword“new”.Thefollowingexampleillustrateshowtocreateanobjectandhowtoaccessinstancevariables:

classEnglish

{

intstudents;

intweeks;

intdays;

}

classOneEnglishCourse

{

publicstaticvoidmain(Stringargs[])

{

EnglishENG101=newEnglish();

inttotalDays;

ENG101.students=10;

ENG101.weeks=4;

ENG101.days=3;

totalDays=ENG101.weeks*ENG101.days;

System.out.println(“TheEnglish101courseisatotalof“+totalDays+”days”);

}

}

Figure2.2–CreateNewObjectandAccessInstanceVariables

ProgramOutput:TheEnglish101courseisatotalof12days

Line12createsanewobject( EnglishENG101=newEnglish(); )bycombiningtwosteps.AccordingtoJavaABeginner’sGuideSixthEdition(2014),thetwostepscombinedcanberewrittenlikethefollowingtoshoweachstepindividually(page106):

1. EnglishENG101;-TheleftsideoftheassignmentwhichdeclaresavariablecalledENG101ofclasstypeEnglish

2. ENG101=newEnglish();-TherightsideoftheassignmentwhichcreatesacopyoftheobjectandgiveENG101areferencetotheobject

ENG101isacreation(knownasinstance)ofEnglishaftercreatingthenewobject.Lines15–17assignvaluestotheinstancevariablesbyaccessingthevariablesusingthedot(.)operator.Thefollowingisthesyntaxforutilizingthedotoperator:

SyntaxobjectName.MemberName;

Thedotoperatorconnectsanobjectwithamember(instancevariableormethod).Inthisexample,anobjectname(ENG101)islocatedontheleftandtheinstancevariables(students,weeks,days)arelocatedontheright.Anobjectholditsowninstancevariablecopydefinedbytheclass.Therefore,ifmultipleobjectsexist,eachobjectcanholda

differentvaluethantheotherobject.Thefollowingexampleillustrateacreationoftwoobjects(ENG101andENG202):

classEnglish

{

intstudents;

intweeks;

intdays;

}

classTwoEnglishCourses

{


{



inttotalDays101;

inttotalDays202;

ENG101.students=10;

ENG101.weeks=4;

ENG101.days=3;

ENG202.students=12;

ENG202.weeks=6;

ENG202.days=3;

totalDays101=ENG101.weeks*ENG101.days;

System.out.println(“TheEnglish101coursehas“+ENG101.students+”studentsandthecourselast“+totalDays101+”days”);

totalDays202=ENG202.weeks*ENG202.days;

System.out.println(“TheEnglish202coursehas“+ENG202.students+”studentsandthecourselast“+totalDays202+”days”);

}

}

Figure2.3–TwoObjectsCreated

ProgramOutput:TheEnglish101coursehas10studentsandthecourselast12days

TheEnglish202coursehas12studentsandthecourselast18days

Lines12and13createtwoobjects(ENG101andENG202)thenassignvaluestobothobjectsinlines18–24.Recall,ifmultipleobjectsexisttheneachobjectcanholdadifferentvaluethantheotherobject.Inthisexample,adifferentvalueisassignedtovariables“studentsandweeks”butvariable“days”containsthesamevalue“3”forbothobjects.

Note:TheconventionforvariablesarelowerCamelCasewhereeachwordinthevariablenamebeginswithacapitalletterexceptthefirstword.However,ENG101andENG202isanexceptionwhichcontainsallcapitallettersbecauseschoolcoursesnormallyhaveallcapitallettersbeforeanumberintheircoursename.

MethodsAmethodisablockofcodesurroundedbycurlybracketsthatperformaspecificaction/task.Thepurposeistomanipulateandprovideaccesstodatadefinedbytheclass.Inotherwords,amethodperformsactionsonthedata.Itisbestforallmethodstocarryoutasingletask.Forexample,agoodmethodwillonlyperformasingletaskofaddingnumbersbutnotaddingnumbersandsavingdatatoafile.Theprogrammaybecomedifficulttoreadandunderstandifamethodcarriesoutmorethanonetask.

Methodsconsistofaheaderandbody.Themethodheaderincludesamethodtypeandamethodname.TheconventionformethodnameissimilartoavariablenamewhichconsistofalowerCamelCasestyle.Eachwordbeginswithacapitalletterexceptthefirstword.Succeedingthemethodnameisarequiredpairofparenthesiswhichsetsapartvariablesfrommethods.Thefollowingisthesyntaxformethod:

SyntaxmethodTypemethodName(parameter-list)

{

//MethodBody

}

ThemethodType(knownasreturntype)determinesthedatatypereturnedbythemethod.Aprogrammerisforcedtousekeyword“void”forthemethodTypeifnovaluesarereturned.ThemethodNamecanbeanynameexceptaJavakeyword.Agoodtechniquetoemployfornamingamethodisverb-nouncombinations,suchas“getOrderoraddNumbers”.Methodbodyiswherecodewillbeexecutedtocarryoutatask.Theparameterlistarevariablesthatreceiveargumentspassedtothemethod.Ifthemethodhasnoparametersthentheparameterlistmustremainempty.

Note:AmethodsignatureisthemethodNameandparameterlist.

MethodReturns

Methodreturnsareconceptsthatreturnavaluefromamethodortransfercontroloutofamethod.Bothconceptsareachievedbyusingthereturnkeyword.Executionisterminatedandsubsequentstatementswithinthemethodareskippednomatterwherethereturnkeywordislocated.Thefollowingaretwomethodreturntypes:

1. Methodsthatreturnavalue2. Methodsthatcannotreturnavalue

AccordingtoORACLE,amethodreturnstothecodethatinvokeditwhenit

completesallthestatementsinthemethod,reachesareturnstatementorthrowsanexception

whicheveroccursfirst.

Note:Usually,thereturnkeyword(alsoknownasreturnstatement)isnotusedformethodsthatcannotreturnavalue.Itisnotusedbecauseallofthecodewithinthemethodiscompletedbeforeexecutingthereturnkeyword.However,ifthereturnkeywordisused,thenitwillbeimplementedattheendofthemethodtotransfercontrol.

ReturnAValue

Mostmethodsreturnavaluewhichspecifiestheoutcomeofacalculationorresult(pass,fail,etc.)Thereturnvalueisrequiredtobethesamedatatypeasthemethodtype.Forinstance,ifthemethodtypeisan“int”datatypethenthereturntypemustbean“int”datatype.Thefollowingisasyntaxandexampleforamethodreturn:

Syntaxreturnvalue;

classEnglish

{

intstudents,weeks,days;

inttotalDays()

{

https://docs.oracle.com/javase/tutorial/java/javaOO/returnvalue.html

returnweeks*days;

}

}


{


{



ENG101.students=10;

ENG101.weeks=4;

ENG101.days=3;

ENG202.students=12;

ENG202.weeks=6;

ENG202.days=3;

System.out.println(“TheEnglish101coursehas“+ENG101.students+”studentsandthecourselast“+ENG101.totalDays()+”days”);


}

}

Figure2.4–ReturnaValue



Methodsreturnavaluetothecodethatcalledthemethod.Inthisexample,lines26and27makecallstothemethod( inttotalDays() )atline5.Thenthemethodreturnstheoutcomefromcalculation( weeks*days )backtolines26and27.Thedot(.)operatorconnectsbothobjects(ENG101andENG202)toamember(totalDays())whichisamethod.Themethodisplacedontherightsideofthedotoperatorwhiletheobjectsarelocatedontheleft:

ENG101.totalDays();ENG202.totalDays();

Line3declaresallinstancevariablesasan“int”datatype.Thereforetheinstancevariables(weeksanddays)usedforcalculationatline7isautomaticallydeclaredwithan“int”datatype.Thiswillnotcauseareturnerrorbecausethereturntype(line7)andmethodtype(line5)possessthesamedatatype.Thevaluesforeachinstancevariablearecalculatedbasedonlines19,20,23,and24.Lines19and23containvaluesforvariable“weeks”whilelines20and24containvaluesforvariable“days”.

ReturnNoValue

Methodsthatcannotreturnavaluearecalledvoidmethods.Thekeyword“void“isimplementedasthemethodTyperatherthanadatatypesuchas“int”.Anerroroccursifthereisanattempttoreturnavaluefromthevoidmethod.Thefollowingisavoidmethodexample:

classEnglish

{


voidtotalDays()

{

System.out.println(weeks*days);

}

}


{


{



ENG101.students=10;

ENG101.weeks=4;

ENG101.days=3;

ENG202.students=12;

ENG202.weeks=6;

ENG202.days=3;

System.out.println(“HowmanystudentsareintheEnglish101course?“+ENG101.students);

System.out.println(“Thecourseis“+ENG101.days+”daysfor“+ENG101.weeks+”weeks.”);

System.out.print(“Thereforethecourselastthefollowingtotalnumberofdays:”);

ENG101.totalDays();

System.out.println(“\n”);

System.out.println(“HowmanystudentsareintheEnglish202course?“+ENG202.students);

System.out.println(“Thecourseis“+ENG202.days+”daysfor“+ENG202.weeks+”weeks.”);

System.out.print(“Thereforethecourselastthefollowingtotalnumberofdays:”);

ENG202.totalDays();

}

}

Figure2.5–VoidMethod

ProgramOutput:HowmanystudentsareintheEnglish101course?10

Thecourseis3daysfor4weeks.

Thereforethecourselastthefollowingtotalnumberofdays:12

HowmanystudentsareintheEnglish202course?12

Thecourseis3daysfor6weeks.

Thereforethecourselastthefollowingtotalnumberofdays:18

Line5displayskeyword“void”whichindicatesthemethodwillnotreturnanyvalues.Nevertheless,thevoidmethodonlyperformsataskofcalculatingthetotalofnumberofdays.Line7printsthetotaldaysaftermultiplyingweeksanddays.Thefollowingdisplaysanerrorwhenthevoidmethodimplementsthereturnkeywordwithavalue:

classEnglish

{


//Avoidmethodcannotreturnavalue

voidtotalDays()

{

returnweeks*days

}

}

Figure2.6–VoidMethodError

PassArgumentsToParameters

Argumentsarevaluespassedtoamethodwhileparametersreceivesthevalues.Inotherwords,parametersreceivearguments.Parametervariablesaredeclaredwithinamethod’sparenthesisandoperatelikealocalvariable.Localvariablesandparametervariablesareonlyvisibletothemethodwhereisdeclared.Itisimportanttoknowthatoneormoreargumentscanbepassedtoindividualparameters.Thefollowingisanexampleofpassingtwoargumentstotwoparameters:

classEnglish

{

inttotalDays(intwk,intd)

{

returnwk*d;

}

}


{


{



System.out.println(“TheEnglish101courseisatotalof“+ENG101.totalDays(4,3)+”days”);

System.out.println(“TheEnglish202courseisatotalof“+ENG202.totalDays(6,3)+”days”);

}

}

Figure2.7–PassArgumentsToParameters

ProgramOutput:TheEnglish101courseisatotalof12days

TheEnglish202courseisatotalof18days

Line3definestwoparameters“wk,d”formethodtotalDays().MethodscanhavemorethanoneparameterbyseparatingeachparameterwithacommaLines16and17indicatesthearguments“4,3”forobject“ENG101”and“6,3”forobject“ENG202”arepassedtoparameters“wk,d”

Note:Objectscanbepassedtoamethodandreturnedfromamethod.

MethodTypes

Thefollowingarethefourtypesofmethods:

1. InstanceMethods2. ClassMethods3. MainMethod4. Constructors

InstanceMethods

Instancemethodsarecalled(knownasinvoked)byusinganobject.Thereforeaninstancemethodissimilartoaninstancevariablewherebybothmemberscanbeaccessedthroughinitializedobjects.However,instancevariablescanbeaccessedwithanobjectreferenceorwithoutanobjectreference.Thefollowingisaninstancemethodexample:

publicclassLion

{

voidsound()

{

System.out.println(“ROAR”);

}


{

LionmaleLion=newLion();

maleLion.sound();

}

}

Figure2.8–InstanceMethod

ProgramOutput:ROAR

Lines3–6startsandcompletestheinstancemethod“sound”Line10createsanobject“maleLion”usingkeyword“new”Line11callstheinstancemethod“sound”throughinitializedobject“maleLion”

ClassMethods

Aclassmethod(knownasstaticmethod)issimilartoaclassvariablewherebytheyaredeclaredwithastatickeyword.Thestatickeywordmeansthememberbelongstotheclassandsharedbetweenallobjects.Classmethodscanbeaccessedviatheobjectnameorclassname.However,awarningappearswhenaccessingthemethodbyanobject.Thereforethefavoredwaytoaccessclassedmethodsisthroughclassname.Thefollowingisaclassmethodexample:classStaticAddNumbers

{

staticinta,b;

staticintaddNumbers()

{

returna+b;

}

}

classStaticExample

{

publicstaticvoidmain(String[]args)

{

StaticAddNumbersobjAdd=newStaticAddNumbers();

objAdd.a=20;

StaticAddNumbers.b=30;

System.out.println(“Theadditionofvariables‘a+b’is“+objAdd.addNumbers()+”andaccessedbyanobject”);

System.out.println(“Theadditionofvariables‘a+b’is“+StaticAddNumbers.addNumbers()+”andaccessedbyaclassname”);

}

}

Figure2.9–ClassMethod

ProgramOutput:Theadditionofvariables‘a+b’is50andaccessedbyanobject

Theadditionofvariables‘a+b’is50andaccessedbyaclassname

Line3declarestwoclass/staticvariables“a,b”Lines5–7definestheclass/staticmethod“addNumbers”Line17assigns20toclassvariable“a”.Notice,thewarningnexttoline17thatstates“ThestaticfieldStaticAddNumbers.ashouldbeaccessedinastaticway”.Thiswarningmeanstheclassvariable(knownasstaticvariable)ispreferredtobeaccessedbyclassname.Line18doesnothaveawarningbecauseclassnameprecedesthevariablename“b”Line20issimilartoline18.Awarningmessageappearsbecausethestaticmethodisaccessedviaobjectnameratherthanclassname“i.e.,line21”

Note:Classmethodscanonlyaccessclassvariablesandonlycallotherclassmethods.

MainMethod

Themainmethodisuniqueandmandatoryifaparticularclassbeginstheprogram.Thismethodisrequiredbecauseitexecutestheprogram.Thefollowingisthesyntaxformainmethod:

Syntaxpublicstaticvoidmain(String[]args)

{

//MethodBody

}

Thereareseveralexamplesofthemainmethodbutthefollowingexplainseachcomponent:

public-themethodcanbeaccessedbyallclassesstatic–themethodissharedbetweenallobjectsvoid–themethoddoesnotreturnanyvaluesString[]args–themethodreceivesaStringargumentandpasstheargumenttotheprogram

Note:ThemainmethodisexplainedinthischapterbecausePart2–Java4SeleniumWebDriverfocusesonJavaprogramming.However,SeleniumWebDriverwritesimplechecksusesatestingframeworksuchasJUnitandTestNGthatwillnotrequirethemainmethod.Thenextbook“SeleniumWebDriverforFunctionalAutomationTesting”willfocusonSeleniumanddiveintoJUnit.

Constructors

Aconstructorisaspecialmethodthathasthesamenameastheclass.Ifaconstructorisnotdefinedthenablankconstructorisautomaticallycreated.Consequentlyallclassescontainaconstructorwhichinitializeobjectsofaspecificclass.Anewobjectcallsaconstructoreverytimetheobjectiscreated.Bydefault,theinstancevariablesare

initializedtozerofornumerictypes,nullforreferencetypes,andfalseforbooleantypes.

Constructorshavetheabilitytosettheinitialvalueforaninstancevariable.Recallaninstancevariablecanbeaccessedandassignedavalueusingthedotoperator.InFigure2.4–ReturnAValue,thefollowinginstancevariableswereassignedvalues:

ENG101.students=10;

ENG101.weeks=4;

ENG101.days=3;

ENG202.students=12;

ENG202.weeks=6;

ENG202.days=3;

Constructorscontainparameterswhichreceiveargumentswhenanobjectiscreated.Thefollowingexampleillustrateshowtopassargumentstoaconstructor:

classEnglish

{


English(ints,intw,intd)

{

students=s;

weeks=w;

days=d;

}

inttotalDays()

{

returnweeks*days;

}

}


{


{

EnglishENG101=newEnglish(10,4,3);

EnglishENG202=newEnglish(12,6,3);



}

}

Figure2.10–ParameterizedConstructor



Line5–10createaconstructorwhichdefinesthreeparameters“s,w,d”online5.Eachparameterisusedtoinitializetheinstancevariables“students,weeks,days”onlines7-9.Afterlines22and23areexecuted,thevalues“10,4,3”forENG101andvalues“12,6,3”forENG202areassignedtotheparameters“s,w,d”.Asaresult,thevaluesarepassedtotheEnglish()constructorwhenthekeyword“new”createseachobject“ENG101andENG202”.

Note:Constructorsarenotdefinedwithamethodtypesuchasintorvoid.Noticehowline5beginswithEnglishthendefinetheparameters.Javaallowsaclasstocontainmultiple

constructors.Thefeatureiscalledconstructoroverloadingiftheconstructorscontainadifferentparameterlist.

AccessorMethods

Accessormethodsaremethodsusedtogetandsetvaluesofprivatevariables.Privatevariablescanonlybeaccessedbycodewithinitsownclass.Thereforetheaccessormethodsaretwomethodsknownasgettersandsettersdefinedinthesameclassastheprivatevariables.

Bothmethodsaredefinedwithaprefixthatbeginswith“get”and“set”beforethemethodname.Forexample,getDays()andsetDays()areregardedasaccessormethodstogetthenumberofdaysthensetthenumberofdays.Thefollowingisanexampleofbothaccessormethods:

classEnglish

{

privateintstudents,weeks,days;

English(ints,intw,intd)

{

students=s;

weeks=w;

days=d;

}

intgetStudents()

{

returnstudents;

}

intgetWeeks()

{

returnweeks;

}

intgetDays()

{

returndays;

}

voidsetStudents(ints)

{

students=s;

}

voidsetWeeks(intw)

{

weeks=w;

}

voidsetDays(intd)

{

days=d;

}

inttotalDays()

{

returnweeks*days;

}

}

Figure2.11–AccessorMethods

Line3declaresalloftheinstancevariables“students,weeks,anddays”asprivateLines5–10istheconstructormethod

Lines12–25arethegetaccessormethods.Eachmethodonlyget/returnthenumberofstudents,weeks,anddaysLines27–40arethesetaccessmethods.Eachmethodsets/modifiesthenumberstudents,weeks,anddays

ThisKeywordTheword“this”isakeywordwhichoperatesasareferenceinsideinstancemethodsand/orconstructors.Itreferstothecurrentobjectormemberofthecurrentobjectwhosemethodisbeingcalled.Thekeyword“this”isoptionalbutusefulwhenaprogrammerdecidestohideinformation.Inaddition,thekeyword“this”preventsuncertaintyinaprogramwhenalocalvariableandinstancevariablecontainthesamename.Awarningmessagestates“Theassignmenttovariablenamehasnoeffect”ifbothvariableshavethesamename.Thefollowingexampleshowshowtousekeyword“this”whenthelocalvariableandinstancevariablecontainthesamename:

publicclassThisKeyword

{

inttestVariable=34;

voidhideInstanceVariable()

{

inttestVariable=15;

System.out.println(“WhatisthevalueofthelocalvariableNOTusingthekeyword‘this’?“+testVariable);

System.out.println(“Whatisthevalueoftheinstancevariableusingthekeyword‘this’?“+this.testVariable);

}


{

ThisKeywordobjHide=newThisKeyword();

objHide.hideInstanceVariable();

}

}

Figure2.12–ThisKeyword

ProgramOutput:WhatisthevalueofthelocalvariableNOTusingthekeyword‘this’?15

Whatisthevalueoftheinstancevariableusingthekeyword‘this’?34

Line3declaresandinitializesaninstancevariable“testVariable”toavalueof34Line7declaresandinitializesalocalvariable“testVariable”toavalueof15Line9printamessagewhichincludesthelocalvariable“testVariable”Line10printsamessagewhichincludestheinstancevariable“this.testVariable”usingthekeyword“this”

AnnotationsAccordingtodictionary.com,annotationmeans,“acriticalorexplanatorynote.”RecallfromPart1–Java4SeleniumWebDriver,commentsarenotesthathelpprogrammersunderstandtheprogram.Anannotationissimilartoacommentwherebytheybothprovideinformation.However,commentsareignoredbythecompilerwhileannotationssupplydatatothecompiler.Annotationsprovidemetadatawhichisdatathatdescribesdata.

Allannotationsstartwithanat“@”symbolandspecifythepurposeofamethod.Someannotationscanbecustomizedtoreplacecommentsandpredefinedannotationssuchas@Override.ThefollowingareexamplesofthreeJUnitannotationsusedinSeleniumWebDriver:

1. @Before–allocateresourcesandexecuteonetimebeforeeachtest2. @Test–executesatestscript3. @After–releaseallocatedresourcesandexecuteonetimeaftereachtest

Note:DetailsoftheJUnitannotationsareusedandexplainedinthe“SeleniumWebDriver”books.

http://dictionary.reference.com/browse/annotation?s=t

AccessModifiersAccessmodifiersarehelpfulfeaturesofobject-orientedprogramming.Theyarehelpfulbecauseoftheaccesslimitationitplacesoneveryclassandclassmembers(variablesandmethods).InJava,therearefourkindsofaccessmodifiers:

1. public–indicatesamembercanbeaccessedbyallclasses2. protected–indicatesamembercanbeaccessedbyallclassesandsubclasses(see

InheritanceinChapter4)withinitsownpackage(seePackagesinChapter5)3. nomodifier–indicatesamembercanbeaccessedbyallclasseswithinitsown

package4. private–indicatesamembercanbeaccessedwithinitsownclass

Theaccessmodifierprecedesaclass,variable,andmethoddeclaration.Classescanonlyusethepublicmodifierornomodifier.Therefore,anerroroccursifaclassmakesuseofaprivateorprotectedaccessmodifier.Thefollowingisanexampleofaclass,method,andvariablesusingapublicmodifier:

publicclassEnglish

{

publicintstudents,weeks,days;

publicinttotalDays()

{

returnweeks*days;

}

}


{


{



ENG101.students=10;

ENG101.weeks=4;

ENG101.days=3;

ENG202.students=12;

ENG202.weeks=6;

ENG202.days=3;



}

}

Figure2.13–PublicClass,Variables,andMethod

Theclass(line1),allofthevariables(line3),andmethod(lines5-8)aredeclaredwithapublicaccessmodifier.Consequently,therearenoerrorsandthememberswithintheEnglishclasscanbeaccessedbycodefromtheclass“TwoEnglishCourses”.

Thefollowingisanexampleofaprivatemethod:

publicclassEnglish

{

publicintstudents,weeks,days;

privateinttotalDays()

{

returnweeks*days;

}

}


{


{



ENG101.students=10;

ENG101.weeks=4;

ENG101.days=3;

ENG202.students=12;

ENG202.weeks=6;

ENG202.days=3;



}

}

Figure2.14–PrivateMethod

Line5declaresthemethodtotalDays()withaprivateaccessmodifier.Thatmeansonlymemberswithinitsclass“English”canaccessthemethod.Lines26and27attemptstocallmethod“totalDays()”butcannotbecausetheyarelocatedinadifferentclass“TwoEnglishCourses”.Asaresult,anerrormessagestates“ThemethodtotalDays()”fromTypeEnglishisnotvisible.Thefollowingisanexampleofoneprivatevariableandtwopublicvariables:

Figure2.15–PrivateandPublicInstanceVariables

Line3declaresinstancevariable“students”asprivatewhileline4declaresinstancevariables“weeksanddays”aspublic.Noticelines19–25,twoerrors“lines19and23”occurfortheprivatevariable“students”.Inaddition,thereisanerroronlines27and28whichstates“ThefieldEnglish.studentsisnotvisible”.TheprivatevariableisonlyvisibletotheEnglishclassbutnotvisibletotheclass“TwoEnglishCourses”.However,thepublicvariablesarevisibletobothclasses.Thefollowingareaccesslevelsforeachmodifier:

public protected nomodifier private

Class Yes Yes Yes Yes

Package Yes Yes Yes No

Subclass Yes Yes No No

World Yes No No No

Figure2.16–AccessModifierLevels

StaticKeywordThestatickeywordcanbeappliedtovariables,methods,blocks,andnestedclasses.Usually,themembersofaclassareaccessedthroughanobjectoftheclassviathedotoperator.Whenamemberisdeclaredasstatic,themembercanbeaccessedpriortocreatinganobject.Howevertoaccessastaticmember,itisbesttoprecedethestaticmemberwithaclassnameanddotoperatorratherthantheobjectnameanddotoperator.Awarningmessageappearsifthestaticmemberisprecededbyanobjectnameanddotoperator.Thefollowingisthesyntaxandexampleofastaticvariable:

SyntaxClassName.variableName;classStaticAddNumbers

{

staticinta;

intb;

intaddNumbers()

{

returna+b;

}

}

classStaticExample

{


{

StaticAddNumbersobjAdd=newStaticAddNumbers();

objAdd.b=50;

StaticAddNumbers.a=25;

System.out.println(“Thevalueof‘objAdd.b’is“+objAdd.b);

System.out.println(“Thevalueof‘a’is“+StaticAddNumbers.a);

System.out.println(“Thetotalof‘a+b’is“+objAdd.addNumbers()+“\n”);

StaticAddNumbers.a=30;

System.out.println(“Thevalueof‘a’changedto“+StaticAddNumbers.a+”butthevalueof‘objAdd.b’remains“+objAdd.b);

System.out.println(“Thetotalof‘a+b’is“++objAdd.addNumbers());

}

}

Figure2.17–StaticVariable

ProgramOutput:Thevalueof‘objAdd.b’is50

Thevalueof‘a’is25

Thetotalof‘a+b’is75

Thevalueof‘a’changedto30butthevalueof‘objAdd.b’remains50

Thetotalof‘a+b’is80

Line3declaresastaticvariablenamed“a”withinclass“StaticAddNumbers”.Thevariable“a”isaccessedinlines19,22,25,and26byusingtheclassname,dotoperator,andstaticvariablename.Lines19and25setthevaluewhilelines22and26displaysthevalue.Staticvariablesaretreatedlikeglobalvariablesandinitializedatthestartofexecution.

Chapter2describedclasses,objects,methods,annotations,accessmodifiers,andkeywords“thisandstatic”.Aclassincorporatesdataandcodethatoperatesonthedata.Inaddition,classesprovideatemplateforobjectswhichisthefoundationforobject-orientedprogramming.Methodscarryoutaspecifictaskwhileprovidingaccesstodatadefinedbytheclass.Chapter3willdiscussarraysandstringswhichareregardedasobjectsinJava.

Chapter3ArraysandStrings

Anarrayisacollectionofvariableswiththesamedatatype,samenameandfixednumberofvalues.Thevaluesareaccessedviaanindexwhichidentifiesanitemandstartsatzero.Eachiteminthearrayiscalledanelement.Abenefitofarraysisthecapacitytodealwithalargenumberofrelatedvaluesinoneentity.Forinstance,asinglearrayhastheabilitytoholdeveryemployee’ssalary.

InJava,arraysandstringsareconsideredobjects.Astringisadatatypecontaininganimmutablesequenceofcharacters.Immutablemeansthestringcannotbemodifiedafteraninitializationstatement.However,therearemanymethodsthatcanperformactionsonthestrings.

Chapterthreewilldiscussthefollowingconcerningarraysandstrings:

Single-DimensionalArrays

Multi-DimensionalArrays

For-EachLoop

Strings

Single-DimensionalArraysSingle-Dimensionalarraysarethemostusedtypeofarrays.Itstoresalistofrelatedvaluessuchasdailytemperaturesforaspecificmonth.Inreturn,thelistofvaluescanleadtoamonthlytemperatureaverage.Alloftheinformationstoredinanarrayiseasilyaccessiblebyanindex.Thefollowingaretwosyntaxesfordefiningasingle-dimensionalarray:

SyntaxarrTypearrName[]=newarrType[arrSize];

or

arrTypearrName[];arrName=newarrType[arrSize];

Parameter Description

arrType Determinesthedatatypeofeachvalueinthearray

arrName Nameofthearray

new Allocatesmemoryforthearray

arrSize Numberofvaluesinthearray

Figure3.1–SingleDimensionSyntaxDetails

Thefollowingisanexampleofasingle-dimensionalarray:

publicclassOneDimensionalArray

{


{

int[]tempMay=newint[3];

tempMay[0]=105;

tempMay[1]=102;

tempMay[2]=98;

System.out.println(“ThehighesttemperatureinMaywas“+tempMay[0]+”degrees”);

System.out.println(“The2ndhighesttemperatureinMaywas“+tempMay[1]+”degrees”);

System.out.println(“The3rdhighesttemperatureinMaywas“+tempMay[2]+”degrees”);

}

}

Figure3.2–Single-DimensionalArrayExample

ProgramOutput:ThehighesttemperatureinMaywas105degrees

The2ndhighesttemperatureinMaywas102degrees

The3rdhighesttemperatureinMaywas98degrees

Line5initializesthearray“tempMay”byusingthekeyword“new”.Thenumber3inbrackets[3]indicatethearraycontain3elementsLines7–9assignvaluestoeachofthearray.Thefirstvalueisstoredatindexposition0.Zeroisalwaysthestartingpositionforarrays.Inthisexample,thelastindexpositionis2.Elements0–2holdsatotalof3elements.

Arrayscanbeassignedvaluesononelinewithoutthekeyword“new”.Thefollowingisanotherwaytoassignvaluestoanarray:

publicclassOneDimensionalArray

{


{

int[]tempMay={105,102,98};

System.out.println(“ThehighesttemperatureinMaywas“+tempMay[0]+”degrees”);

System.out.println(“The2ndhighesttemperatureinMaywas“+tempMay[1]+”degrees”);

System.out.println(“The3rdhighesttemperatureinMaywas“+tempMay[2]+”degrees”);

}

}

Figure3.3–AlternateSingle-DimensionalArrayExample

ProgramOutput:ThehighesttemperatureinMaywas105degrees

The2ndhighesttemperatureinMaywas102degrees

The3rdhighesttemperatureinMaywas98degrees

Line5initializesthearray“tempMay”andassignsthreevaluestothearray.Noticethekeyword“new”isnotusedtoinitializethearray.However,thedatatype“int”isspecifiedalongwiththearraynameandvalues.Squarebracketsindicatesanarraywhilethenumberofvalueswithinthecurlybracketsdictatethearraysize.ThefollowingisadiagramdisplayingthearrayvaluesfromFigure3.2andFigure3.3:

Figure3.4–ArrayName,Values,andIndexes

Multi-DimensionalArraysMulti-Dimensionalarraysareregardedasanarrayofarrays.Thereforetwoormorebracketsmustbeusedtodeclareamulti-dimensionalarray.Themostcommontypeofmulti-dimensionalarrayisatwo-dimensionalarray.Eachdimensioncontainsitsownsetofbrackets.Aspreadsheetwithrowsandcolumnsisagoodwaytoimagineatwo-dimensionalarray.Thefirstpairofbracketsarerowsandsecondpairofbracketsarecolumns.Thefollowingisthesyntaxandexampleforatwo-dimensionalarray:

SyntaxarrTypearrName[][]=newarrType[arrSize1][arrSize2];

publicclassTwoDimensionalArray

{


{

introw,column;

inttestTwoDimension[][]=newint[2][3];

for(row=0;row<2;row++)

{

for(column=0;column<3;column++)

{

testTwoDimension[row][column]=(row*3)+column+1;

System.out.print(testTwoDimension[row][column]+”“);

}

System.out.println();

}

}

}

Figure3.5–Two-DimensionalArrayExample

ProgramOutput:123

456

Line7initializesthetwo-dimensionalarray“testTwoDimension”byusingthekeyword“new”.Twobracketsindicatetherearetwodimensionssimilartorowsandcolumns.Noticetheoutputproducesatotaloftworowsandthreecolumns.Line9representsthecountforrowswhileline11representsthecountforcolumnLine13calculatesthevaluesonethroughsixLine14printsthevaluesonethroughsix

Comparabletosingle-dimensionalarrays,atwo-dimensionalarraycanbedeclaredandinitializedwithoutthekeyword“new”.Thefollowingisanexampleofatwo-dimensionalarraywithoutbeinginitializedusingkeyword“new”.


{


{

introw,column;

inttestTwoDimension[][]=

{

{1,2,3},

{4,5,6}

};


{




}

}

}

Figure3.6–AlternateTwo-DimensionalArrayExample

ProgramOutput:123

456

Lines7–11initializethearraybysurroundingeachdimension’slistwithinaseparatesetofbrackets.Noticehoweachelementisdividedbyacommaandeachsetofbracketsrepresentarow.Theprevioustwoexamplesoutputthesameinformation.Aspecificvaluecanbeprintedbyindicatingaspecificrowandcolumn.Thefollowingexampleprintsaspecificvalueaccordingtoadefinedrowandcolumn:


{


{

introw,column;

inttestTwoDimension[][]=

{

{1,2,3},

{4,5,6}

};


{




}

System.out.println(“\n”+“Whatvalueislocatedinrow1-column2?“+testTwoDimension[1][2]);

}

}

Figure3.7–PrintASpecificValueFromATwo-DimensionalArray

ProgramOutput:123

456

Whatvalueislocatedinrow1-column2?6

Thefollowingillustratestheoutputinaspreadsheetformat:

Figure3.8–SpecificIndexForATwo-DimensionalArray

For-EachLoopThefor-eachloop(knownasenhancedforloop)wasestablishedtocyclethroughacollectionofobjectssuchasanarray.Thistypeofcontrolstructurepresentsthesamefunctionalityastheforloop(seeChapter4-ControlStructuresin(Part1)Java4SeleniumWebDriver)whichexecutesablockofcodeacertainnumberofiterations.However,thefor-eachloopexecutesablockofcodewhilecyclingthrougheachelementinthecollection.Thefollowingisthefor-eachloopsyntax:

Syntaxfor(collTypeitrVariable:collection){statement(s)}

SyntaxDetails

Argument Description

collType Referstothetypeofdataforthecollection

itrVariable Referstothenameoftheiterationvariablethatreceiveseachelementaftereveryiteration

collection Thecollectionsuchasarraythatwillbeiteratedorcycledthrough

statement(s) Theblockedofthatwillbeexecuted

{…} Theopeningandclosingcurlybrackets

Figure3.9–For-EachLoopSyntaxDetails

Allelementsinthefor-eachloopareretrievedandstoredintheitrVariable.Thelooprepeatsuntilallelementsarereadinindexorder.Itisimportanttoknowthatthecolltypemustbethesametypeastheobject.Inthecaseofarrays,thecollTypemustbethesametypeasthearrType.Thefollowingisanexampleoffor-eachloop:

publicclassForEachLoop

{


{

double[]costPerItem={12.34,56.78,99.99};

doubletotalCost=0;

for(doublei:costPerItem)

{

System.out.println(“Thecostis“+i);

totalCost=totalCost+i;

}

System.out.println(“\n”+“Thetotalcostofallitemsis“+totalCost);

}

}

Figure3.10–ForEachLoopExample

ProgramOutput:Thecostis12.34

Thecostis56.78

Thecostis99.99

Thetotalcostofallitemsis169.11

Line5and6initializeandassignvaluestothearray“costPerItem”and“totalCost”Line8retrieveseachelement(12.34,56.78,99.99)inarray“costPerItem”Line10printseachelementLine11calculatesthetotalofallelements

Note:Lines8–11canbereadas”Foreachdoubledatatypeinthe“costPerItem”array,printeachelementandcalculatethetotalofallelements”.

Two-DimensionalArrayIteration

Iterationsfortwo-dimensionalarraysoperatesimilartosingle-dimensionalarrays.Theiterationvariableforatwo-dimensionalarraymustreferencethesingle-dimensionalarray.Itmustreferencethesingle-dimensionalarraybecausetwo-dimensionalarraysareconsideredarraysofarrays.Thereforeeachtwo-dimensionalarrayiterationretrievesthenextarray.Thefollowingisanexampleofatwo-dimensionalarrayiteration:


{


{

inttotalCost=0;

int[][]costPerItem=

{

{5,10},

{15,20},

{25,30}

};

for(inti[]:costPerItem)

{

for(intj:i)

{

System.out.println(“Thecostis“+j);

totalCost=totalCost+j;

}

}

System.out.println(“\n”+“Thetotalcostofallitemsis“+totalCost);

}

}

Figure3.11–Two-DimensionArrayIterationExample

ProgramOutput:Thecostis5

Thecostis10

Thecostis15

Thecostis20

Thecostis25

Thecostis30

Thetotalcostofallitemsis105

Line5initializesandassignszero“0”tototalCostLines6–11initializeandassignvaluestothetwo-dimensionalarray“costPerItem”Line13“ for(inti[]:costPerItem) ”referencesasingle-dimensionalarraywherebyeachiterationretrievesthenextarrayincostPerItemfromstarttofinish“index0toindex5”Line15“ for(intj:i) ”cyclesthrougheachelement

SearchAnArray

Arrayscanbesearchedtoretrievespecificvalues.Therearetimeswhenonlyacertainvalueisneededfromacollectionofvalues.Thefollowingexampleillustrateshowtoretrieveaspecificvaluefromanarray:


{


{

intspecificCost=20;

int[][]costPerItem=

{

{5,10},

{15,20},

{25,30}

};

for(inti[]:costPerItem)

{

for(intj:i)

{

if(j==specificCost)

{

System.out.println(“Thespecificcostof“+”’”+specificCost+”’”+”waslocatedinthecollectionofvalues”);

}

}

}

}

}

Figure3.12–SearchATwo-DimensionalArray

ProgramOutput:Thespecificcostof‘20’waslocatedinthecollectionofvalues

Line5initializesandassigns20tovariable“specificCost”Lines6–11initializeandassignvaluestothetwo-dimensionalarray“costPerItem”Line13“ for(inti[]:costPerItem) ”referencesasingle-dimensionalarraywherebyeachiterationretrievesthenextarrayincostPerItemfromstarttofinish“index0toindex5”Line15“ for(intj:i) ”cyclesthrougheachelementLine17searchesthetwo-dimensionalarrayforaspecificelement“20”viavariablespecificCost

StringsAstringisadatatypecontaininganimmutablesequenceofcharacters.Thisdatatypeisconsideredanobjectsoitwasnotdiscussedin(Part1)Java4SeleniumWebDriverwiththeotherdatatypes.Therearetwowaystocreateastring:

1. StringLiteral2. Stringusingthekeyword“new”

Thefollowingisanexampleofastringliteral:

publicclassStringObject

{


{

StringfirstName=“Rex”;

StringlastName=“Jones”;

System.out.println(“Stringsareplacedwithinquotationmarks”);

System.out.print(“Thefirstnameis“+firstName+”andlastnameis“+lastName+“.”);

System.out.println(”Bothnamesweredeclaredandinitializedasstrings.Asequenceofcharacters”);

}

}

Figure3.13–StringExample

ProgramOutput:Stringsareplacedwithinquotationmarks

ThefirstnameisRexandlastnameisJones.Bothnamesweredeclaredandinitializedasstrings.Asequenceofcharacters

Lines5and6declareandinitializeastringdatatypeLines8–10displaysthestringliteralwithintheprintlnmethod()

Stringscanbecreatedlikeotherobjectsbyusingthekeyword“new”whichcallstheStringconstructor.ThefollowingisanexampleofaStringwiththekeyword“new”:

Stringname=newString(“RexJones”);

StringOperations

InJava,thereisaStringclasswhichcontainsmanymethodsforoperations.ThefollowingisascreenshotofseveralStringmethodsperEclipse:

Figure3.14–StringMethods

Line7displaysalistofmethodsaftertypingaperiodafterthevariable“name”Adescriptionofaspecificmethod“equals”appearswhenitishighlighted

ThefollowingarepopularStringmethods,theirdatatype,anddescription:

1. charAt(intindex):char-Returnsthecharacteratthespecifiedindex2. compareTo(str):int-Returnslessthanzeroifthecallingstringislessthanstr,

greaterthanzeroifthecallingstringisgreaterthanstr,andzeroifthestringsareequal

3. concat(Stringstr):String-Concatenatesthegivenstringattheendofthestring4. equals(ObjectanObject):boolean–Comparesthestringtoaspecificobject5. equalsIgnoreCase(Stringstring):boolean-Comparestringsandignorethecases6. indexOf(Stringstr):int-Returnstheindexofthefirstoccurrenceofaspecified

substring7. lastindexOf(Stringstr):int-Returnstheindexofthelastoccurrenceofastring8. length():int-Returnsthelengthofastring9. replace(charoldChar,charnewChar):String-Returnsthenewstringafter

changingalloccurrencesoftheoldstring10.split(Stringregex):String[]-Splitsthestringandreturnsastringarray

thatmatchesthegivenregularexpression11.toLowerCase():String-ConvertsallofthecharactersinaStringtolowercase12.toUpperCase():String-ConvertsallofthecharactersinaStringtouppercase13.trim():String-Returnsacopyofthestring,afterdeletingleadingandtrailingwhitespacesfromtheoriginalstring

Astringdatatypecannotbecombinedwithadifferentdatatypeforanoperationsuchasmultiplication,subtraction,ordivision.Forexample,astringvalueof“534000.00”appearstobeanumericvaluebutstringdoesnotallowmathematicaloperationsunlessatypewrapperconvertsthestring.Thevalue“534000.00”resemblesadoubledatatype.However,anerroroccursifcombinedwithadoubledatatype.Thefollowingexampledisplaysanerrorifastringdatatypeiscombinedwithasubtractionoperator:


{


{

StringgrossIncome=“534000.00”;

doublegross=534000.00;

doubletaxes=225000.00;

doublenetIncome;

netIncome=grossIncome-taxes;

netIncome=gross-taxes;

System.out.println(“Thenetincomeis“+netIncome);

}

}

Figure3.15–StringErrorDueToMathematicalOperations

Line5declaresandinitializesaStingvalue“534000.00”Line10displaysanerrorbecauseStringsdonotallowmathematicaloperations.However,noticeline11doesnotdisplayanerrorbecausebothvariables“grossandtaxes”aredeclaredasadoubledatatype“lines6and7”

TypeWrappers

Typewrappersareusedtoconvertstringsintoprimitivetypes(byte,double,float,integer,long,short).Thereforethepreviousexamplewhichdisplayedanerrorforstringvalue“534000.00”canbeconvertedintoanumber.Typewrappersareusedtowraptheprimitivetype.Thefollowingisanexampleofhowtoreturnadoublewhenthevalue“534000”isspecifiedasastring:


{


{

StringgrossIncome=“534000.00”;

doubletaxes=225000.00;

doublenetIncome;

netIncome=Double.parseDouble(grossIncome)-taxes;

System.out.println(“Thenetincomeis“+netIncome);

}

}

Figure3.16–ReturnsADoubleAfterReadingAStringValue

ProgramOutput:Thenetincomeis309000.00

Line5declaresandinitializesaStingvalue“534000.00”Line9parses(knownasreads)thestring“grossIncome”thenreturnadoubledatatype.Afterwards,thevariabletaxes“225000”issubtractedfromvariablegrossIncome“534000”andthevalueisassignedtovariable“netIncome”

Thefollowingisalistoftypewrappersthatconvertastringdatatype:

Wrapper ConversionMethod

Double Double.parseDouble(string)

Float Float.parseFloat(string)

Long Long.parseLong(string)

Integer Integer.parseInteger(string)

Short String.parseString(string)

Byte Byte.parseByte(string)

Figure3.17–TypeWrappers

Chapter3explainedarraysandstringswhichareobjects.Anarrayisacollectionofvariableswiththesamedatatype,samenameandfixednumberofvalues.Astringisadatatypecontaininganimmutablesequenceofcharacters.Chapter4willdefineinheritancewhichisahierarchicalconcept.Theconceptallowscodeandobjectstobereused.

Chapter4Inheritance

Inheritanceisahierarchicalconceptwhichallowsreusablecodeandobjectstobeextended.Aclassknownassuperclasscanbecreatedwithvariablesandmethodstheninheritedbyotherclasses.Theinheritedclassesarecalledsubclasses.Eachsubclassthatinheritsthesuperclassmembersarepermittedtoaddtheirownclassmembers.Forexample,adogisananimal,sotheclass“Dog”,wouldbeasubclassofAnimal.Acatisananimalandtheclass“Cat”wouldalsobeasubclassofAnimal.Inbothexamples,class“Animal”isthesuperclass.

ChapterfourwillexplainthefollowingregardingInheritance:

FundamentalofInheritance

SuperclassObject

InheritingPrivateMembers

SuperclassandSubclassConstructors

Polymorphism

Abstraction

KeywordFinal

FundamentalsofInheritanceTheconceptofinheritingclassesisanimportantfoundationwithinobject-orientedprogramming.Functionalitiesareaddedtoanexistingclasswhichpreventsthesamecodefrombeingwrittenmultipletimes.Thesubclassinheritsallclassmembersfromthesuperclass.Anotherwaytoviewsuperclassandsubclass,istothinkofsuperclassastheparentandsubclassasthechild.

Inorderforthesubclasstoinheritthesuperclass,thekeyword“extends”mustbeusedintheclassdeclaration.Keyword“extends”meansthesubclasswilladdtothesuperclass.Subclassesarenotallowedtoinheritmultiplesuperclasses.However,asubclassisallowedtobecomeasuperclassforanadditionalsubclass.Asaresult,theadditionalsubclassinheritsallclassmembersfromeachsuperclass.Thefollowingisthesyntaxforasubclassinheritingasuperclass:

SyntaxclassSubClassNameextendsSuperClassName

{

//ClassBody

}

Thefollowingisanexampleforasubclassinheritingasuperclass:

classSchool

{

intnumTeachers;

intnumStudents;

voidshowNumberOfPeople()

{

System.out.println(“Thereare“+numTeachers+”teachersand“+numStudents+”students”);

}

}

classElementarySchoolextendsSchool

{

StringprincipalName;

inttotalTeacherStudents()

{

returnnumTeachers+numStudents;

}

voiddisplayPrincipal()

{

System.out.println(“Theprincipalnameis“+principalName);

}

}

classSchoolDistrict

{


{

ElementarySchoolBishopHeights=newElementarySchool();

ElementarySchoolAltaMesa=newElementarySchool();

BishopHeights.numTeachers=10;

BishopHeights.numStudents=130;

BishopHeights.principalName=“JoeDoe”;

System.out.println(“MyelementaryschoolisBishopHeights\n”);

BishopHeights.displayPrincipal();

BishopHeights.showNumberOfPeople();

System.out.println(“Thereforethetotalofteachersandstudentsis“+BishopHeights.totalTeacherStudents());

}

}

Figure4.1–SubclassExtendsSuperclassExample

ProgramOutput:MyelementaryschoolisBishopHeights

TheprincipalnameisJoeDoe

Thereare10teachersand130students

Thereforethetotalofteachersandstudentsis140

Line1displayssuperclass“School”Line11usesthekeyword“extends”tocreatesubclass“ElementarySchool”whichinheritssuperclass“School”Line17utilizevariables“numTeachersandnumStudents”ofthesuperclassLines29and30displaytwoobjects“BishopHeightsandAltaMesa”Lines32and33assignvalues“10and130”tovariables“numTeachersandnumStudents”whichareinheritedfromsuperclass“School”Line34assignavalue“JoeDoe”tovariable“principalName”whichisamemberofsubclass“ElementarySchool”

Thesubclass“ElementarySchool”isauniquetypeofsuperclass“School”.MoresubclassessuchasHighSchool,University,etc.caninheritsuperclass“School”.The“ElementarySchool“classinheritsallofthe“School“classmembersthenaddavariable

“principalName”andtwomethods“totalTeacherStudentsanddisplayPrincipal”.Noticehowline30createsanobjectthatwasnotutilized.ThisshowsthatmoreElementarySchoolobjectscanbecreatedtoaccessmembersofthesuperclass“School”.

Note:Objectsfromthesuperclassdonothaveknowledgeofthesubclass.Therefore,thesuperclassobjectscannotaccessthesubclass.

SuperclassObjectThesuperclass“Object”isthehighestsuperclassofallclasses.Inotherwords,thereisnoparentclassabovethe“Object”superclass.Bydefault,the“Object”superclassincludesmethodsthatareinheritedbyallsubclasses.ThefollowingisascreenshotwhichshowsObject“java.lang.Object”bydefaultastheSuperclasswhencreatinganewclass:

Figure4.2–EclipseNewClassCreationModal

InheritingPrivateMembersPrivatemembersthatareinheritedfromthesuperclassremainprivateinthesubclass.Thereforethesubclasscannotaccesstheprivatemembers.Variablesandmethodsareonlyaccessiblebycodewithinitsownclasswhichdoesnotincludesubclasses.Nevertheless,theprivatememberscanbeaccessedbyusingaccessormethods.

SuperclassandSubclassConstructorsSuperclassesandsubclassescontaintheirownconstructorswhichinitializeobjectsofitsclass.Asaresult,theconstructorsareindependentofeachother.Thesuperclassdoesnothaveaccesstothesubclassconstructorsbutthesubclasshasaccesstothesuperclassconstructors.Subclassescallasuperclass’sconstructorbyutilizingthekeyword“super”.Thefollowingisthesyntaxforasubclasscallingasuperclassconstructor:

Syntaxsuper(parameter-list)

Thefollowingisanexampleofasubclassinheritingasuperclass:

classSchool

{

privateintnumTeachers,numStudents;

School(intt,ints)

{

numTeachers=t;

numStudents=s;

}

intgetTeachers(){returnnumTeachers;}

intgetStudents(){returnnumStudents;}

voidsetTeachers(intt){numTeachers=t;}

voidsetStudents(ints){numStudents=s;}

voidshowNumberOfPeople()

{

System.out.println(“Thereare“+numTeachers+”teachersand“+numStudents+”students”);

}

}

classElementarySchoolextendsSchool

{

privateStringprincipalName;

ElementarySchool(Stringp,intt,ints)

{

super(t,s);

principalName=p;

}

inttotalTeacherStudents()

{

returngetTeachers()+getStudents();

}

voiddisplayPrincipal()

{

System.out.println(“Theprincipalnameis“+principalName);

}

}

classSchoolDistrict

{


{

ElementarySchoolBishopHeights=newElementarySchool(“JoeDoe”,10,130);

System.out.println(“MyelementaryschoolisBishopHeights\n”);

BishopHeights.displayPrincipal();

BishopHeights.showNumberOfPeople();

System.out.println(“Thereforethetotalofteachersandstudentsis“+BishopHeights.totalTeacherStudents());

}

}

Figure4.3–SubclassInheritsSuperclassExample

ProgramOutput:MyelementaryschoolisBishopHeights

TheprincipalnameisJoeDoe

Thereare10teachersand130students

Thereforethetotalofteachersandstudentsis140

Line3declaresallofthevariables“numTeachersandnumStudents”asprivateLines5–9istheconstructorforsuperclass“School”Lines11–14aretheaccessormethods“getandset”Lines25–29isthesubclassconstructorfor“ElementarySchool”whichcallsthesuperclassconstructor“School”.Thestatement“super(t,s);”online27referstothesuperclassconstructorviakeyword“super”

Note:Asuperclassconstructorisexecutedfirstiftheprogramincludesasuperclassconstructorandsubclassconstructor.

PolymorphismPolymorphismisasignificantconceptinobject-orientedprogramming.Thisconceptallowsoneinterfacetobeutilizedbymultiplemethods.Inthecaseofsuperclassandsubclass,asuperclassprovideastructurewherebyasubclasscandefineitsownmethodoperation.Themethodsareinheritedautomaticallywhenthesubclassextendsthesuperclass.

MethodOverridingvsMethodOverloading

Methodoverridingisafeaturewhenthesubclassmethodoverridesthesuperclassmethod.Bothmethodsmusthavethesamemethoddatatypeandsignature.Amethod’ssignatureconsistsofamethod’snameandparameterlist.Thesuperclassmethodcanbecalledalthoughitisoverriddenbyasubclassmethod.Itisoverriddenifthekeyword“super”anddot(.)operatorisfollowedbythemethodname:super.methodName();

Methodoverloadingistwoormoremethodsinthesameclasswiththesamenamebutadifferentparameterlist.Theparameterlistdetermineswhichoverloadedmethodisexecutedifacallismadetothemethodname.Howeveraduplicatemethoderroroccursifmultiplemethodshavethesamesignature.Thefollowingshowsthedifferencesbetweenmethodoverridingandmethodoverloading:

MethodOverriding MethodOverloading

Definition Thesuperclassandsubclasshasamethodwiththesamemethodtypeandsignature

Aclasshasmultiplemethodswiththesamenameanddifferentparameterlist

MethodType

Thesuperclassandsubclassmethodtypesmustbecompatible

Thetypecanbethesameordifferent

Signature Thesuperclassandsubclassmusthavethesamesignature

Thesignaturesaredifferentregardingnumberofparameters,typeofparameters,andorderofparameters

Figure4.4–DifferencesBetweenMethodOverridingandOverloading

Note:An“@Override”annotationcanbeusedtoinstructthecompilerofasubclassoverridingasuperclass.Annotationsmaketheprogrameasiertoreadandletsthecompilerverifyiftheoverrideisvalid.

StaticBinding

Bindingistheconnectionbetweenamethodcallandthemethoddefinition.Staticbinding(knownasearlybinding)iswhenbindingoccursatcompiletime.Thereforebindinghappensbeforeaprogramexecutes.Thefollowingisanexampleofstaticbinding:

classBinding

{

voidprintClassName()

{

System.out.println(“ThisclassiscalledBinding”);

}

}

classBindingExtendextendsBinding

{

@Override


{

System.out.println(“ThisclassiscalledBindingExtend”);

}

}

classBindingExamples

{


{

BindingExtendobjBindingExtend=newBindingExtend();

objBindingExtend.printClassName();

}

}

Figure4.5–StaticBindingExample

ProgramOutput:ThisclassiscalledBindingExtend

Line11displaysanannotationwhichindicatesthesubclassmethod“printClassName()”willoverridethesuperclassmethod“printClassName()”Line12displaysaniconnexttothelinenumberwhichhasatooltipthatstates“overridesBinding.printClassName”Line22createsanobject“objBindingExtend”ofclass“BindingExtend”Line23callsthemethoddefinition“printClassName()”

Note:Forstaticbinding,thecompilerverifiesifamethoddefinition“printClassName”existinclass“BindingExtend”.

DynamicBinding

Dynamicbindingiswhenbindingoccursatruntime.Thereforethistypeofbindinghappenswhentheprogramisrunning.Unlikestaticbinding,dynamicbindingallowspolymorphism.Thereforeamethodoverrideisgoodillustrationofdynamicbinding.Thefollowingisanexampleofdynamicbinding:

classBinding

{


{

System.out.println(“ThisclassiscalledBinding”);

}

}

classBindingExtendextendsBinding

{

@Override


{

System.out.println(“ThisclassiscalledBindingExtend”);

}

}

classBindingExamples

{


{

BindingobjBinding=newBinding();

objBinding.printClassName();

BindingobjBindingExtend=newBindingExtend();

objBindingExtend.printClassName();

}

}

Figure4.6–DynamicBindingExample

ProgramOutput:ThisclassiscalledBinding

ThisclassiscalledBindingExtend

Lines3and12definethesamemethodname“printClassName()”foreachclass“BindingandBindingExtend”Lines22and25createsbothobjects“objBinding”and“objBindingExtend”Lines23and26iswheredynamicbindingtakesplace.Bothcallsaremadetothesamemethodname“printClassName()”butindifferentclasses“superclassandsubclass”.Theobjects“objBinding”and“objBindingExtend”areusedforbindingatruntime.

AbstractionAbstractionappliestoclassesaswellasmethods.Thekeyword“abstract”isusedtocreateabstractclassesandmethods.Anabstractclasscannotbeinstantiatedsoitisusedasasuperclass.Abstractmethodsaredeclaredwithoutanimplementationsoitdoesnotincludeabody.Abstractclassescanincludeabstractmethodsandimplementedmethods.However,anabstractclasscannotcontainobjectsduetoincompleteimplementationofitsmethods.

Thepurposeofabstractclassesistoonlydefineageneralizedmethodthenallowasubclasstodefinethedetailsofthemethod.Therearesituationswhenasuperclasscannotcreateameaningfulmethodimplementation.Aninstancemethodcanbedeclaredabstractbutstaticmethodsandconstructorscannotbedeclaredabstract.Thefollowingisthesyntaxforanabstractclassandmethod:

Syntax–AbstractClass

abstractclassClassName{

//AbstractClassescancontainabstractmethodsandimplementedmethods

//AbstractMethod

abstractmethodTypemethodName(parameter-list);

//ImplementedMethod

methodTypemethodName(parameter-list)

{

//MethodBody

}

}

Syntax–AbstractMethod

abstractmethodTypemethodName(parameter-list);

Note:Asubclassmustbedeclaredasabstractorimplementalloftheabstractmethodsfromthesuperclass.

KeywordFinalThekeyword“final”preventsaclassormethodfrombeingoverwritten.Methodsareimplicitlydeclaredasfinaliftheclassisdeclaredfinal.RecallfromPart1–Java4SeleniumWebDriver,thekeyword“final”isusedtodeclareandinitializeconstants.Constantsareunchangeablevaluesassignedtoavariablename.Thebenefitofusingkeyword“final”istoconfirmaclassorclassmemberwillnotchangebecauseitiscriticaltotheprogram.Asaresult,anerroroccursifthereisanattempttoinheritaclassoroverrideaclassmember(methodorvariable)declaredasfinal.

Chapter4explainedinheritance,superclass,andsubclass.Inheritanceisahierarchicalconceptwhichallowsreusablecodeandobjectstobeextended.Superclassistheparentclasstosubclasswherebysubclassinheritstheclassmembers.Chapter5willdiveintopackageswhichisagroupofrelatedclasses.

Chapter5Packages

Apackageisacollectionofrelatedclasseswherebythepackageoperateslikeafoldertoorganizecode.Theclasseswithinapackageareaccessedbythepackagename.RecallfromPart1–Java4SeleniumWebDriver,thatanerroroccursifaclassmakesuseoftheprivateaccessmodifier.However,aclasscanbemadeprivateandnotaccessedbycodeoutsideofthepackagebyusingnomodifier.Apackagedefinesauniquenamespacewhichpreventsmultipleclassesofhavingthesamenamewithinapackage.InJava,thereisnoproblemwithdifferentpackagesusingthesameclassname.

Chapter5willexplainthefollowingregardingpackages:

CreateAPackage

ImportAPackage

JavaClassLibrary

CreateAPackageAprogrammercancreatetheirownpackagetogroupclasses.Allclasseshaveapackagethatisstoredinadirectory.Thefirstlineinmostsourcefilesincludesapackagestatement.However,apackagestatementisoptionalsothefirstlinecanremainblank.Ablankpackagestatementisthedefaultwhichcontainsnoname.Itisimportanttoknowthatdifferentsourcefilesareallowedtousethesamepackagestatement.Thefollowingisthesyntaxforapackagestatement:

Syntaxpackagepackagename;

Thenameofeachpackage“e.g.,packagename”iscasesensitive.InJava,itisconventionaltousealllowercaselettersforapackagename.Alllowercaselettersforapackageservesasacleardistinctionfromclassnames,methodnamesandmostvariablenames.EclipseIDEdisplaysawarningifthefirstletterwithinpackagenamebeginswithacapitalletter.Thefollowingisascreenshotwhichshowsawarningifthefirstletterisacapitalletter:

Figure5.1–PackageNamingConvention

Thefollowingisanexampleofapackagestatement:

packageexamplepackage;

classPackageTest

{

voidprintTest()

{

System.out.println(“Thisisatest”);

}

}

publicclassPackage

{


{

System.out.println(“Thisisanothertest”);

}

}

Figure5.2–PackageStatement

ProgramOutput:Thisisanothertest

Line1containsthepackagestatement“packageexamplepackage”Line3beginstheclassdefinitionforclass“PackageTest”.Thisclassisacomponentofapackage“examplepackage”Line11beginstheclassdefinitionforclass“Package”.Thisclassisacomponentofapackage“examplepackage”

Thefollowingisascreenshotoftheclassesgroupedtogetherinapackagedirectory:

Figure5.3–PackageDirectoryScreenshot

ImportAPackageAJavapackageisimportedbyusingthekeyword“import”.Importsareusefulwhenaclasswantstoaccessamemberinanotherclass.Theotherclasscanbeinthesamepackageordifferentpackage.Afterimportingapackage,themembersofthepackageareuseddirectlywithoutanyadditionalsyntax.Thefollowingisthesyntaxforimportingapackage:

Syntaximportpackagename.ClassName;

Toimportaclass,thedot(.)operatorisplacedbetweenthepackagenameandclassname.Theimportstatementsmustbeenteredafterthepackagestatementbutbeforetheclassesaredeclaredinthecurrentfile.Thefollowingisanexampleofapackagestatement,importstatement,andaclassdeclaration:

packageexamplepackage;

importexamplepackage.PackageTest;

publicclassPackageOne

{


{

PackageTestobjPackage=newPackageTest();

objPackage.printTest();

}

}

Figure5.4–PackageImport

ProgramOutput:Thisisatest

Line1containsthepackagestatement“packageexamplepackage;”Line2containstheimportstatement“importexamplepackage.PackageTest;”.Thepackagenameis“examplepackage”andclassnameis“PackageTest”whichislocatedinadifferentfile.Line4beginstheclassdeclaration“publicclassPackageOne”Line8createsanobject“objPackage”usingtheimportedclass“PackageTest”Line10callsthemethod“printTest();”whichislocatedinclass“PackageTest”.ViewFigure5.2-PackageStatement,toseedetailsofthemethod.

Note:Alloftheclassesfromaspecificpackagecanbeimportedbyusingthepackagenameandanasterisk:importpackagename.*;

JavaClassLibraryTheJavaClassLibraryisknownasJavaApplicationProgrammingInterface(API)whichprovidesprogrammerswithacollectionofprewrittenclasses.Eachprewrittenclasshelpssupportthelogicofaprogrambysupplyingusefulfunctions.Oneofthepackagescalledjava.langisautomaticallyimportedintoallprograms.ThereforeclassessuchasSystemisemployedautomaticallywhenusingtheprint()andprintln()methodstodisplayinformation.AccordingtoOracle,thefollowingshowsfourofmanyJavaClassLibraries:

java.lang–ProvidesclassesthatarefundamentaltothedesignoftheJavaprogramminglanguage.

java.io-Providesforsysteminputandoutputthroughdatastreams,serializationandthefilesystem.

java.math-Providesclassesforperformingarbitrary-precisionintegerarithmetic(BigInteger)andarbitrary-precisiondecimalarithmetic(BigDecimal).

java.sql-ProvidestheAPIforaccessingandprocessingdatastoredinadatasource(usuallyarelationaldatabase)usingtheJavaTMprogramminglanguage.

Note:Packagejava.langcontainsamathclasswhichisdifferentfrompackagejava.math.Themathclasswithinjava.langcontainsmethodsthatperformsbasicnumericoperations.

Chapter5describedpackagesinJava.Eachpackagecontainsagroupofrelatedclasses.Theclassesareaccessedbythepackagename.Animportstatementmustbeplacedintheprograminorderforaclasstoutilizemembersofanotherclass.Chapter6willlookintointerfaceswhichisagroupofrelatedmethods.

https://docs.oracle.com/javase/7/docs/api/

Chapter6Interfaces

Aninterfaceisacollectionofrelatedmethods.Interfacesarecomparabletoaclasswherebyitcontainsvariablesandmethods.Howeverbydefault,aninterface’svariableisdeclaredpublic,static,andfinalwhilethemethodisdeclaredabstract.Itispossibleforaninterfacetoperformataskbutusuallythereisnobehaviorimplementation.Inotherwords,mostmethodsinaninterfacedonotcontainabody.Thereforeaninterfacemethodwithoutabodyonlyincludesamethod’ssignature.Asaresult,theinterfacedefineswhattasktoperformbutnothowtoperformthetask.Theclasswhichimplementstheinterfacedecideshowtoperformthetask.Interfacescanextendoneormoreinterfacessimilartoasubclassextendingasuperclass.Thefollowingisthesyntaxforaninterface:

SyntaxaccessmodifierinterfaceinterfaceNameextendsinterfaceName1,interfaceName2,interfaceNameN

{



variableTypevariableNameN;

methodTypemethodName1(parameter-list);


methodTypemethodNameN(parameter-list);

}

SyntaxDetails

Argument Description

accessmodifier Canbepublicornoaccessmodifier.Apublicdeclarationindicatestheinterfacecanbeusedbyanycode.Anoaccessmodifieristhedefaultwhichindicatestheinterfaceisonlyavailabletomembersofitspackage

interface Akeywordusedtodeclareaninterface

interfaceName Thenameofaninterface

extends Anoptionalkeywordthatextendsoneormoreinterfaces

interfaceName1,2,N Oneormoreinterfacesseparatedbyacommathatwillbeextended

variableTypevariableName1,2,N; Oneormoreinterfacevariables


Oneormoreinterfacemethods

Figure6.1–InterfaceSyntaxDetails

Thefollowingisaninterfaceexample:

publicinterfaceInterfaceTest

{

publicvoidmethodOne();

publicvoidmethodTwo();

}

Figure6.2–InterfaceExample

Line3declaresaninterfacebyusingthekeyword“interface”witha“public”accessmodifier.Thereforethecodecanbeimplementedbyanyclasswithinanypackage.ThenameoftheinterfaceiscalledInterfaceTest.Lines5and6arevoidabstractmethods“methodOneandmethodTwo”.Thekeyword“abstract”isnotneededwithinaninterface.Noticethesemi-colonatthe

endofeachmethod.Thesemi-colonisplacedattheendofthemethodsbecausethereisnobody/implementation.

Chaptersixwilldiscussthefollowingregardinginterfaces:

InterfaceImplementation

InterfaceVariables

MultipleInheritance

DefaultInterfaceMethod

InterfaceImplementationInterfacesareimplementedusingkeyword“implements”andoneormoreclassesprovideimplementationforthemethods.Ifaclassdoesnotimplementamethodbyprovidingabodythentheclassmustbedeclaredasabstract.Eachclassmayimplementthesameinterfacedifferentlywhilesupportingthesamemethods.Itisimportanttoknowthatoneclasscanimplementmultipleinterfaces.Thefollowingisthesyntaxforaclassimplementinganinterface:

SyntaxclassClassNameextendsSuperClassNameimplementsinterfaceName

{

//ClassBody

}

Thefollowingisanexampleofaclassimplementinganinterface.

packageInterfaceTesting;

publicclassInterfaceExamplesimplementsInterfaceTest

{

publicvoidmethodOne()

{

System.out.println(“ThisisthebodywhichimplementsmethodOne”);

}

publicvoidmethodTwo()

{

System.out.println(“ThisisthebodywhichimplementsmethodTwo”);

}


{

InterfaceTestobjInterface=newInterfaceExamples();

objInterface.methodTwo();

}

}

Figure6.3–ClassImplementsAnInterface

ProgramOutput:ThisisthebodywhichimplementsmethodTwo

Note:Thescreenshotdisplaysasplitimageduetotheinterfaceandclassbeinginseparatefiles.Eclipsedisplaysamessagewhichstates“interfacemustbedefinedinitsownfile”iftheinterfaceandclassislocatedinthesamefile.

Line3includesthe“implements”keywordwithintheclassdefinitionLines5–12aretheimplementedmethodswhichhasabody.Eachclassmethodmustmatchtheinterfacemethod.Thereforethemethodsaredeclared“public”,“void”methodtype,andsamesignature.Theclasswouldhavebeendeclaredasabstractifoneofthemethodswerenotimplemented.Anabstractclassresemblesthefollowingdeclaration:

abstractpublicclassInterfaceExamplesimplementsInterfaceTest

InterfaceVariablesInterfaceconstants(knownasconstants)areimplicitlydeclaredaspublic,static,andfinal.Inotherwords,interfacevariablesarebydefaultconstantsinitializedwithavalue.Constantsareunchangeablevaluesassignedtoavariablename.Thevaluesareestablishedinaninterfacewithoutamethodandsharedacrossallfiles.Aclassimplementstheinterfacevariablesinthesamemannerasmethods.Thefollowingisanexampleofaninterfacevariable:

publicinterfaceInterfaceVariable

{

intDAYS_PER_WEEK=7;

intMAX_HOURS_PER_DAY=24;

}

Figure6.4–InterfaceVariableExample

MultipleInheritanceMultipleinheritanceiswhenaninterfaceextendsanotherinterfaceoraclassimplementsmultipleinterfaces.Thekeyword“extends”isusedtoextendaninterface.Anextensionofinterfacesisbeneficialifaprogrammerelectstoaddmoremethods.Errorsaredisplayedifamethodisaddedtotheoriginalinterfaceandtheinterfacehasalreadybeenimplementedbyaclass.Alloftheclasseswhichusedtheoriginalinterfacewillbreakexistingcodebecausethereisnoimplementationofthenewlyaddedmethod.Howevertheoriginalinterfacecangetextendedtoaccommodatethenewmethodinaseparateinterface.Programmerscandecidetoeithercontinueusingtheoriginalinterfaceorstartusingtheextendedinterface.

Aclassinheritsmultipleinterfacesbyusingthekeyword“implements”followedbytheinterfaceswhichareseparatedusingacomma.Aclassmustprovideimplementationsforallmethodsiftheinterfaceinheritsanotherinterfaceortheclassimplementsmultipleinterfaces.Thefollowingisanexampleofmultipleinheritanceforaninterface:

publicinterfaceExtendInterfaceextendsInterfaceTest

{

publicvoidmethodThree();

publicvoidmethodFour();

}

Figure6.5–InterfaceExtendExample

Line3usesthe“extends”keywordtoextendsaninterface“InterfaceTest”.Theextendedinterfacecontainsabstractmethods“methodOneandmethodTwo”fromFigure6.2InterfaceExampleLines5and6displaypublicvoidabstractmethods“methodThreeandmethodFour”.Themethodsfromtheextendedinterfacearenotneededwheninheritinganinterface.Additionalinterfacescanbeextendedbyaddingtheinterfacenameandseparatingallinterfacingwithacomma

Thefollowingisanexampleofaclassimplementingmultipleinterfaces:

publicclassMultipleInterfacesimplementsInterfaceTest,ExtendInterface

{

publicvoidmethodOne()

{

System.out.println(“ThisisthebodywhichimplementsmethodOne”);

}

publicvoidmethodTwo()

{

System.out.println(“ThisisthebodywhichimplementsmethodTwo”);

}

publicvoidmethodThree()

{

System.out.println(“ThisisthebodywhichimplementsmethodThree”);

}

publicvoidmethodFour()

{

System.out.println(“ThisisthebodywhichimplementsmethodFour”);

}


{

InterfaceTestobjInterface1=newMultipleInterfaces();

objInterface1.methodOne();

ExtendInterfaceobjInterface3=newMultipleInterfaces();

objInterface3.methodThree();

}

}

Figure6.6–ClassImplementingMultipleInterfaces

ProgramOutput:ThisisthebodywhichimplementsmethodOne

ThisisthebodywhichimplementsmethodThree

Line3usesthe“implements”keywordtoimplementmultipleinterfaces“InterfaceTestandExtendInterface”Lines5–21implementsabody/behaviorforeachmethoddefinedinbothinterfacesLines25–29createobjects“objInterface1andobjInterface3”thatisusedtocallmethods“methodOneandmethodThree”

DefaultInterfaceMethodAdefaultinterfacemethod(knownanextensionmethod)allowsaninterfacemethodtoprovideabody.Therefore,theinterfacemethodsarepermittedtoimplementabehavior.ThischangeoccurredinthereleaseofJDK8wherebyaninterfacehastheoptiontoremainabstractordefineadefaultimplementation.Defaultmethodscontaina“default”keywordwhichprecedesthemethodtype.Anadvantageofdefaultmethodsisaclassdoesnotrequireimplementation.Howeveraclassrequiresimplementationofadefaultmethodifadifferentvalueisreturned.Thefollowingisanexampleofadefaultmethodusingfigures“Figures6.2–InterfaceExampleandFigure6.5–InterfaceExtendExample”.

publicinterfaceDefaultMethod

{

publicvoidmethodOne();

publicvoidmethodTwo();

defaultpublicvoidmethodThree()

{

System.out.println(“ThisisthebodywhichimplementsmethodThree”);

}

defaultpublicvoidmethodFour()

{

System.out.println(“ThisisthebodywhichimplementsmethodFour”);

}

}

Figure6.7–DefaultMethodExample

Chapter6explainedinterfaceswhichisacollectionofrelatedmethods.Generally,the

interfacemethodsdonotcontainabody.Thereforetheinterfacemethodsdefinewhattasktoperformbutnothowtoperformthetask.However,adefaultmethodallowsaninterfacemethodtoprovideabodywhichoccurredinthereleaseofJDK8.Chapter7willdiscusserrors,exceptions,anddebugging.

Chapter7Errors,Exceptions,andDebugging

Allprogramswillincludesomekindoferror.Anerrorisanunwantedproblemintheprogram.Itcanbeanunexpectedproblemsuchasmisspellingakeyword.InJava,theerrorsaregroupedintothreetypes:

1. Syntax–preventscodefromexecuting2. Runtime–generatesanerrorwhentheprogramisexecuting3. Logical–doesnotgenerateanerrormessageduetoafaultinthecode’slogic

Logicalerrorsaredifficulttolocatebecauseanerrormessageisnotgenerated.Usually,logicalerrorsarehiddenuntilaprogrammerdebugstheirprogram.Althougherrorsareunavoidableproblems,someproblemscanbehandledatruntime.Problemshandledatruntimearecalledexceptions.Theprogrammercreatesablockofcodecalledanexceptionhandlerwhichhandleexceptionsinadisciplinedmanner.Abenefitofhandlingexceptionsistheprogramcontinuestorunaftercatchingtheexception.

Debuggingisaprocessthatallowsaprogrammertoobservethencorrectanerror.TheproblemsinaprogramcanbefoundbyusingSystem.out.print,System.out.printlnoradebugger.Adebuggerisatoolthatfollowsacode’slogic.Mostprogrammersprefertouseadebuggerinsteadofseveralprintstatementstoinvestigateaproblem.Ifprintstatementsareused,thentheprogrammermustaddtheprintstatementsandremovetheprintstatementafterresolvingtheproblem.

Chaptersevenwillexplainthefollowingregardingerrors,exceptions,anddebugging.

ErrorTypes

ThrowableExceptionParentClass

Java’sBuilt-InExceptions

CommonExceptions

PrinciplesofHandlingExceptions

Try/CatchBlock

FinallyBlock

CatchAThrowableException

MethodsDefinedByThrowable

ThrowvsThrows

Debugging

ErrorTypesInprogramming,errorsareproblemsthatresultfromamistakeinaprogrammer’scode.Theerrorsarefoundbeforeaprogramexecutes,whenaprogramexecutes,andsometimeshiddenwithinaprogram.Theerrorslocatedbeforeexecutionofaprogramarecalledsyntaxerrors.Errorsfoundduringexecutionofaprogramarecalledruntimeerrors.Thehardesterrorstodiscoverwhicharehiddeninaprogramarecalledlogicalerrors.Nevertheless,allerrorsmustberesolvedtohaveasuccessfulprogram.

SyntaxErrors

Syntaxerrors(knownascompilererrors)stopprogramsfromexecuting.Recallfromthefirstbook“Part1–Java4SeleniumWebDriver”,syntaxisasetofrulesthatspecifiesastructuredcombinationofwordsandsymbols.Ifnotstructuredcorrectly,anerroroccurstopreventthestatementsfromcompiling.Asaresult,theerrorsarenotcompiledduetoaninaccuracyintheprogrammer’scode.

Syntaxerrorsaretheeasiesterrorstolocateandresolve.AnIntegratedDevelopmentEnvironment(IDE)suchasEclipsepointsouttheerrors.Theerrorsaredisclosedbyaredunderlinebeneaththecodeand/orredXtotheleftofalinenumber.Inaddition,atooltipdisplaysamessagethatrevealstheerrorafterhoveringovertheredX.AccordingtoBeginningJava®Programming(2015),syntaxerrorsincludethefollowingexamples(page172):

Misspelledclass,variable,ormethodnames

Misspelledkeywords

Missingsemicolons

Missingreturntypeformethods

Outofplaceormismatchedparenthesesandbrackets

Undeclaredoruninitializedvariables

Incorrectformatofloops,methods,orotherstructures

Thefollowingcodehassyntaxerrorsintheprogram:

publicclassSyntaxError

{


{

intx,y,total;

x=10;

y=6,

Total=x+y;

System.out.println(“Thetotalof10+6is“+total);

}

}

Figure7.1–SyntaxErrorExample

Line10displaysanerrorduetoacommaratherthanasemi-colonLine11displaysanerrorbecauseTotalisnotdeclared.Line7declarestotalbutthefirstletterbeginswithalowercase“t”ratherthananuppercase“T”.

ThefollowingisanexampleofEclipserevealingtheerrorafterhoveringovertheredXforline10:

Figure7.2–ErrorMessageAfterHoveringOverRedX

Theerrorstates“Syntaxerrorontoken“,”,;expected”whichmeansthecompilerexpectsasemi-colon.AgrayXwithacircleandwhitebackgroundappearsaftercorrectingthe

error.Consequently,theredunderlineandredXdisappearafterreplacingthecommawithasemi-colontocompletethestatement.

SomeerrorsdisplayayellowcirclewithasmallerredXsimilartoline11.ThiserroruncoversmultiplesolutionsthatmayresolvetheproblemafterclickingtheredX.ThefollowingisascreenshotofEclipsedisplayingpossiblesolutionstofixtheerroronline11:

Figure7.3–PossibleSolutionsAfterClickingTheRedX

SeveralsolutionsunfoldafterclickingtheredXonline11.However,thecorrectsolutionisthefirstoption“Changeto‘total’”.Eclipseautomaticallyupdatesthecodetoreflecttheselectedproposedsolution.Thereforelines10and11displayagrayXwithacircleandwhitebackground.BothX’sareremovedaftersavingthefile.

RuntimeErrors

Runtimeerrorsaredetectedwhenaprogramexecutesaninvalidaction.Invalidactionsareoperationssuchasdividebyzero.Thesyntaxiscorrectsotheprogramrunsbutaproblemoccursduringruntime.Thefollowingisanexampleofaruntimeerror:

publicclassRuntimeError

{


{

inta,b,x,y;

intresult,sum;

a=x=10;

b=y=0;

result=a/b;

sum=x+y;

System.out.println(“Whatis10/0?”+result);

System.out.println(“Whatis10+0?”+sum);

}

}

Figure7.4–RuntimeErrorExample

ProgramOutput:Exceptioninthread“main”java.lang.ArithmeticException:/byzero

atErrors.RuntimeError.main(RuntimeError.java:13)

Figure7.5–Console/ProgramOutputScreenshot

Line7declaresfourvariables“a,b,x,y”Line8declarestwovariables“result,sum”Line10initializetwoofthevariables“aandb”to10Line11initializetwoofthevariables“xandy”to0Line13initializevariable“result”todivide‘a’by‘b’Line14initializevariablesumtoadd‘x’plus‘y’

Theprogramexecutesbutaruntimeerroroccursduetoline13.Thereforeexecutionimmediatelystopsanddoesnotexecutelines14–17.Although,line14isavalidoperation,thecompilerwillnotexecutethestatement.TheProgramOutputdisplaysamessagewhichinformstheprogrammeroftheproblem.Firstlineindicatesaproblembyshowing“/byzero”meaninganumberwasdividedbyzero.Secondlinespecifieswheretheproblemoccurredbyshowingthepackagename“Errors”,classname“RuntimeError”,methodname“main”,andlinenumber“13”.

LogicalErrors

Logicalerrorsexecutewithoutanerrorbutlogicallyperformsthewrongtask.Asaresult,thistypeoferrorischallengingunlessaprogrammerknowswhattoexpect.Theactualresultsarecomparedtotheexpectedresultstoverifywhatwentwrong.Logicalerrorssuchasusinganoperatorprecedenceincorrectlyormisplacingasemicolonwillexecuteandproduceimproperresults.Thefollowingareexamplesoflogicalerrors:

publicclassLogicalErrors

{


{

inttotal1=(9+(8*7))/6;

inttotal2=(9+8)*(7/6);

inttotal3=9+8*7/6;

inttotal4=(9+8)*7/6;

System.out.println(“Whatistheresultoftotal1:“+total1);




}

}

Figure7.6–OperatorPrecedenceLogicalErrorExample

ProgramOutput:Whatistheresultoftotal1:10

Whatistheresultoftotal2:17



Lines7–10initializeeachvariable“total1,total2,total3,total4”withadifferentoperatorprecedence.Eachvariableproduceadifferentvaluealthoughthevalues“9,8,7,6”arethesame.Thefollowingisanexampleofmisplacingasemicolon:

publicclassLogicalErrors2

{


{

inti;

for(i=0;i<5;i++);

{

System.out.println(“Theloopcontrolvariableis“+i);

}

}

}

Figure7.7–MisplacedSemicolonLogicalErrorExample

ProgramOutput:Theloopcontrolvariableis5

Line9incorrectlyplacesasemicolonattheendoftheforloop.Thereforetheprogramoutputs5ratherthan0,1,2,3,4.

ThrowableExceptionParentClassAnexceptionisaJavaclasswherebyjava.lang.Throwableistheparentclass.Therefore,theThrowableexceptionrepresentsallexceptionclasses.Anobjectofaparticularexceptionclassisgeneratedwhenanexceptionisthrowninaprogram.TherearetwomainsubclassesderivingfromtheThrowableparentclass:

1. Error–containsseriousexceptionsthatoccurintheJavaVirtualMachine(JVM).JVMisamachinewithinamachinewhichsolvesproblemsandhelpstheprogramremainsecure.AnErrorsubclassisnotmanagedbytheprogrammer.

2. Exception–containsexceptionsthatoccurintheprogram.AnExceptionsubclassismanagedbytheprogrammer.

Thisbook“Part2–Java4SeleniumWebDriver”willexplaintheExceptionsubclass.Exceptionsfromsubclass“Error”arebeyondaprogrammer’scontrol.ThefollowingisadiagramfromProgramCreekwhichshowsahierarchyofJavaExceptionclasses:

http://www.programcreek.com/wp-content/uploads/2009/02/Exception-Hierarchy-Diagram.jpeg

Figure7.8–JavaExceptionClassHierarchy

Java’sBuilt-InExceptionsInJava,thereisarespectableamountofexceptionclassesdefinedinsidethejava.langstandardpackage.Thereforesomeexceptionsareautomaticallyavailableduetoanimplicitimportofjava.langintoeveryprogram.MostoftheexceptionsaresubclassesthatoriginatefromastandardtypecalledRuntimeException.RuntimeExceptioncontainsexceptionsthatarenotcheckedbythecompiler.Allotherexceptionsarecheckedbythecompilerandmustbeincludedinamethod’sthrowslist.Thefollowingisalistofuncheckedandcheckedexceptionsdefinedinthejava.langpackage:

UncheckedExceptions Description

ArithmeticException Arithmeticerror,suchasdivide-by-zero.

ArrayIndexOutOfBoundsException Arrayindexisout-of-bounds.

ArrayStoreException Assignmenttoanarrayelementofanincompatibletype.

ClassCastException Invalidcast.

EnumConstantNotPresentException Anattemptismadetouseanundefinedenumerationvalue.

IllegalArgumentException Illegalargumentusedtoinvokeamethod.

IllegalMonitorStateException Illegalmonitoroperation,suchaswaitingonanunlockedthread.

IllegalStateException Environmentorapplicationisinincorrectstate.

IllegalThreadStateException Requestedoperationnotcompatiblewithcurrentthreadstate.

IndexOutOfBoundsException Sometypeofindexisout-of-bounds.

NegativeArraySizeException Arraycreatedwithanegativesize.

NullPointerException Invaliduseofanullreference.

NumberFormatException Invalidconversionofastringtoanumericformat.

SecurityException Attempttoviolatesecurity.

StringIndexOutOfBoundsException Attempttoindexoutsidetheboundsofastring.

TypeNotPresentException Typenotfound.

UnsupportedOperationException Anunsupportedoperationwasencountered.

Figure7.9–JavaUncheckedExceptions

CheckedExceptions Description

ClassNotFoundException Classnotfound.

CloneNotSupportedException AttempttocloneanobjectthatdoesnotimplementtheCloneableinterface.

IllegalAccessException Accesstoaclassisdenied.

InstantiationException Attempttocreateanobjectofanabstractclassorinterface.

InterruptedException Onethreadhasbeeninterruptedbyanotherthread.

NoSuchFieldException Arequestedfielddoesnotexist.

NoSuchMethodException Arequestedmethoddoesnotexist.

ReflectiveOperationException Superclassofreflection-relatedexceptions.

Figure7.10–JavaCheckedExceptions

Note:Inadditiontojava.lang,thefollowingpackagesincludeexceptions:

java.awt java.net

java.awt.color java.rmi

java.awt.datatransfer java.security

java.beans java.text

Figure7.11–PackagesThatIncludeExceptions

CommonExceptionsCommonexceptionsareexceptionsthatoccurfrequentlyinaprogram.Thesetypeofexceptionhappenstonewprogrammersaswellasexperiencedprogrammers.Thefollowingisalistofcommonexceptionsinalphabeticalorder:

ArrayIndexOutOfBoundsExceptionClassCastExceptionIllegalArgumentExceptionIllegalStateExceptionNullPointerExceptionNumberFormatExceptionOutOfMemoryErrorStackOverFlowError

Arraysstartatindexpositionzerowhichstoresthefirstvalue.Thereforethelastindexpositionisonelessthesizeofthecompletearray.AnArrayIndexOutOfBoundsExceptionisthrownwhenaprogramattemptstoaccessanindexoutsidetheboundariesofthearray.ThefollowingisanArrayIndexOutOfBoundsException:

publicclassCommonException

{


{

String[]continents=newString[7];

continents[0]=“Africa”;

continents[1]=“Antarctica”;

continents[2]=“Asia”;

continents[3]=“Australia”;

continents[4]=“Europe”;

continents[5]=“NorthAmerica”;

continents[6]=“SouthAmerica”;

continents[7]=“America”;

System.out.println(“Thereare“+continents.length+”countries”);

}

}

Figure7.12–ArrayIndexOutOfBoundsException/CommonExceptionExample

Line8createsanarraywith7elements“String[]continents=newString[7];”Line17whichcontains“continents[7]=“America”;”isoutofboundsforthearray“continents”Line19isnotexecutedbecausetheerrorcausestheprogramtostop

ProgramOutput:Exceptioninthread“main”java.lang.ArrayIndexOutOfBoundsException:7

atExceptionHandling.CommonException.main(CommonException.java:17)

AccordingtotheProgramOutput,theoutofboundsindexis“7”locatedatline17.Thefirstlineindicatesthereisanexceptionthenshowstheexceptiontype“ java.lang.ArrayIndexOutOfBoundsException ”.Number7specifiestheindexwhichcausestheexception.Thesecondlinedisplayswheretheexceptionislocated” atExceptionHandling.CommonException.main(CommonException.java:17) ”.Thefollowingisatranslationofthesecondline:

Anexceptionoccurredinpackagename”ExceptionHandling”,classname“CommonException”,methodname“main”,atlinenumber17.

PrinciplesofHandlingExceptionsItisunderstoodthatexceptionsareproblemsthatoccuratruntime(duringprogramexecution).Javaallowsanexceptionhandlertohandleexceptionswhichincludebenefits.RemembertheruntimeerrorexamplefromFigure7.4,whereexecutionstoppedduetoadivisionbyzero.Abenefitofhandlingexceptionsistheprogramwillcontinueexecutingafterrespondingtoanerror.Thereforeanerrordoesnotstopprogramexecutionbuttheexceptionhandlerpermitstheprogramtocontinuerunning.InJava,therearefiveinterrelatedkeywordsthatfacilitatethemanagementofhandlingexceptions.Thefollowingisadescriptionofeachkeyword:

1. try–monitorscodewhereanexceptionmightoccur2. catch–handlestheexceptionwhenanerroroccurs3. throw–manuallythrowsacustomexception4. throws–throwsanexceptionthatoccurredfromamethod5. finally–automaticallyexecutescodeafterexitingatryblock

TheJavaVirtualMachine(JVM)catchesallexceptionsiftheexceptionhandlerdoesnotcatchtheexception.JVMdisplaysanerrormessagewhichisgoodfordebuggingbutnotforhandlingexceptions.Itisnotgoodforhandlingexceptionsduetoterminationoftheprogram.

Try/CatchBlockThetry/catchblockallowscodetobetriedtoverifywhetheranexceptionoccurs.Ifanexceptionoccursthentheexceptioniscaughttospecifywhatshouldhappen.Thekeywords“tryandcatch”operatetogetherwhenhandlingexceptions.Tryisusedtocontainthecodethatmaycauseanexceptionwhilecatchmanagestheexception.Bothkeywords“tryandcatch”arecentraltohandlingexceptions.Atryblockisprovidedalongwithoneormorecatchblocks.Itisimportanttoknowthatthetryblockandallcatchblocksarebypassedifnoexceptionoccurs.Thefollowingisthetry/catchblocksyntaxforhandlingexceptions:

Syntaxtry

{

//Codemonitoredbytryblock

}

catch(ExceptionType1excObject)

{

//ExceptionHandlerforExceptionType1

}catch(ExceptionType2excObject)

{


}

Thefollowingisthesyntaxdetailsfortryandcatchblock:

Arguments Description

try Monitorsablockofcodeforanexception

catch Handlesandprocessestheexception

ExceptionType1ExceptionType2

TypeofexceptionthatmustbethenameofaclassinheritedfromtheThrowableclass

excObject Receivesthevalueofanexceptioncaughtbythe

handler.

Figure7.13–SyntaxDetails

Thefollowingisanexampleofatryandcatchexceptionhandler:

publicclassTryCatchBlock

{


{

String[]continents=newString[7];

try

{

System.out.println(“Anexceptionhasnotbeenthrown”);

continents[0]=“Africa”;

continents[1]=“Antarctica”;

continents[2]=“Asia”;

continents[3]=“Australia”;

continents[4]=“Europe”;

continents[5]=“NorthAmerica”;

continents[6]=“SouthAmerica”;

continents[7]=“America”;

System.out.println(“Thereare“+continents.length+”continents”);

}

catch(ArrayIndexOutOfBoundsExceptionexc)

{

System.out.println(“Exception!!!-ArrayIndexOutofBounds.Notavalidcontinent”);

}

System.out.println(“Thislineexecutesautomaticallywhetheranexceptionoccursornot”);

}}

Figure7.14–TryandCatchBlockExample

ProgramOutput:Anexceptionhasnotbeenthrown

Exception!!!-ArrayIndexOutofBounds.Notavalidcontinent

Thislineexecutesautomaticallywhetheranexceptionoccursornot

Line8startsthecodemonitoringprocessforerrorsusingthetryblockLine19forcesanexceptionwhendefiningindexposition7whichisoutsideofthearrayboundaries.ThereforethetryblockisterminatedandtheprogramtransferscontroltothecatchblockLine21doesnotexecuteduetotheexceptionatline19Line23startstheexceptionhandlingprocessbylistingtheexceptiontype“ArrayIndexOutOfBoundsException”withinthecatchblockLine25isexecutedwithinthecatchblockaftertheexceptioniscaughtLine27isexecutedfollowingthecatchblock.Thislineexecutesautomaticallywhetheranexceptionoccursornot.

AcommonpracticeinJavaistoassociatemultiplecatchblockswithatryblock.Eachcatchblockmustincludeauniqueexceptiontypesuchasarithmeticexception,arrayindexoutofboundsexception,etc.Theexceptiontypedetermineswhichcatchblockisexecutedaftercreatingmultiplecatchblocks.Thereforeifthearithmeticexceptiontypeisexecutedthenthearrayindexoutofboundsexceptiontypeisbypassed.Thefollowingisanexampleofatryblockwithmultiplecatchblocks:

publicclassMultipleCatchBlocks

{


{

intoddNumbers[]={11,33,55,77,99,111};

intevenNumbers[]={0,2,4,6,8};

for(inti=0;i<oddNumbers.length;i++)

{

try

{

System.out.println(“Whatis“+oddNumbers[i]+“/”+evenNumbers[i]+“?“

+””+oddNumbers[i]/evenNumbers[i]);

}

catch(ArithmeticExceptionexcept)

{

System.out.println(“Exception!!!-Cannotdivideanumberbyzero”);

}

catch(ArrayIndexOutOfBoundsExceptionexcept)

{

System.out.println(“Exception!!!-Cannotlocatetheindex”);

}

}

}

}

Figure7.15–MultipleCatchBlocks

ProgramOutput:Exception!!!-Cannotdivideanumberbyzero

Whatis33/2?16

Whatis55/4?13

Whatis77/6?12

Whatis99/8?12

Exception!!!-Cannotlocatetheindex

Line17displaysthefirstcatchblockwhichcontainsanarithmeticexception.Catchblocksareevaluatedaccordingtotheirorderofassociationtothetryblock.Thereforethiscatchblockisevaluatedfirstsinceitoccursfirstintheprogram.Theothercatchblockisignoredwhenamatchisfoundforthisexceptiontype.Line19isexecutedwhenthecodereacheszero“0”inarray“evenNumbers[]”Line21displaysthesecondcatchblockwhichcontainsanarrayindexoutofboundsexceptionLine23isexecutedwhenthecodesearchesforanindexthatisnotavailableinarray“evenNumbers[]”.Theothercatchblockisignoredwhenamatchisfoundforthisexceptiontype.

FinallyBlockThefinallyblockisanextensionoftry/catchblock.Thisblockconfirmscertainactionssuchaswritingdatatoafileisperformedwhetheranexceptionoccursornot.Javaallowsthesameactiontobeplacedwithinthetryblockandcatchblock.Ontheotherhand,placingthesamecodeinbothblocks“tryblockandcatchblock”createsduplicatecode.

Forexample,whathappensifthereisnoexceptionanddataneedstobewrittentoafile.Inthisscenario,thetryblockexecutesthecodewhilethecatchblockisbypassed.However,ifthereisanexception,thecatchblockexecutesthecodewhilethetryblockisbypassed.Therefore,aprogrammermustplacecodeinthetryandcatchblockforcertaintythatdataiswrittentoafile.Inprogramming,itisdifficulttoreadandmaintainduplicatecode.Afinallyblockisnotrequiredbutitwillcertainlywritedatatothefilewhenanexceptionisthrownandwhenitisnotthrown.Thefollowingisthesyntaxofatry/catch/finallyblock:

Syntaxtry

{

//Codemonitoredbytryblock

}

catch(ExceptionType1excObject)

{


}catch(ExceptionType2excObject)

{


}finally

{

//Executecodeifexceptionoccursornot

}

Thefollowingisanexampleusingthetry/catch/finallyblock:

publicclassFinallyBlock

{


{

intoddNumbers[]={11,33,55,77,99,111};



{

try

{



}


{


}

catch(ArrayIndexOutOfBoundsExceptionexcept)

{

System.out.println(“Exception!!!-Cannotlocatetheindex”);

}

finally

{

System.out.println(“PerformanAction”);

}

}

}

}

Figure7.16–FinallyBlock


PerformanAction

Whatis33/2?16

PerformanAction

Whatis55/4?13

PerformanAction

Whatis77/6?12

PerformanAction

Whatis99/8?12

PerformanAction

Exception!!!-Cannotlocatetheindex

PerformanAction

Line25startsthefinallyblockattheendofthetry/catchblockLine27isexecutedautomaticallywhenanexceptionisthrownandwhenanexceptionisnotthrown

CatchAThrowableExceptionAThrowableexceptioncanbeutilizedtocatchallexceptionssinceitistheparentclass.ThesuperclassThrowablematchesallofitssubclasseswhichincludesRuntimeException.Inordertocatchexceptionsforbothclasses,thesuperclassandsubclassmustbeimplementedintheirrespectivecatchblock.ThefollowingisaThrowablesuperclassandArithmeticExceptionsubclassexampleusingcodefromFigure7.15:

publicclassSuperSubClassException

{


{

intoddNumbers[]={11,33,55,77,99,111};



{

try

{



}


{


}

catch(Throwableexcept)

{

System.out.println(“Exception!!!-TheThrowableExceptioncaughtanerror”);

}

}

}

}

Figure7.17–ThrowableandArithmeticExceptionExample


Whatis33/2?16

Whatis55/4?13

Whatis77/6?12

Whatis99/8?12

Exception!!!-TheThrowableExceptioncaughtanerror

Line18implementsthesubclassexception“ArithmeticException”insidethefirstcatchblockLine20isexecutedwhenthecodereacheszero“0”inarray“evenNumbers[]”Line22implementstheThrowableexceptioninsidethesecondcatchblockLine24isexecutedwhenthecodesearchesforanindexthatisnotavailableinarray“evenNumbers[]”

TheThrowablesuperclassandsubclassareallowedtocatchexceptionsbyplacingthesubclassinthefirstcatchblock.AnerroroccursiftheThrowableexceptionisimplementedinthefirstblock.Theerrormessagestates“UnreachablecatchblockforArithmeticException.ItisalreadyhandledbythecatchblockforThrowable”.

MethodsDefinedByThrowableAsmentioned,Throwableisasuperclassofeveryexceptionsubclass.ThereforeallexceptionssupportmethodsdefinedbyThrowable.AnexceptioncanbecaughtbyaThrowableexceptionbutitisagenericcatch.ItisbesttouseaspecificexceptionsuchasArithmeticExceptionwhenhandlingexceptions.However,someofthemethodsdefinedbyThrowablecanhelpthesuperclassbemorespecificwhenhandlingexceptions.ThefollowingisalistofThrowablemethods:

Method Description

fillInStackTrace() Fillsinthecompletedexecutionstacktrace

getLocalizedMessage() CreatesalocalizeddescriptionoftheThrowableexception

getMessage() ReturnsadetailmessageoftheThrowableexception

printStackTrace() Printsthestacktrace

printStackTrace(PrintStream) Printsthestacktracetothespecifiedprintstream

printStackTrace(PrintWriter) Printsthestacktracetothespecifiedprintwriter

toString() Returnsashortexceptiondescriptionafterbeingcalledbyprintln()method

Figure7.18–MethodsDefinedbyThrowable

OneofthemostcommonmethodsdefinedbyThrowableistheprintStackTrace()method.Thismethodprintsthestacktrace“standarderrormessage”.ThefollowingisanexampleofprintStackTrace()method:

publicclassThrowableMethod

{


{

intoddNumbers[]={11,33,55,77,99,111};

https://www.cis.upenn.edu/%7Ebcpierce/courses/629/jdkdocs/api/java.lang.Throwable.html#fillInStackTrace%28%29

https://www.cis.upenn.edu/%7Ebcpierce/courses/629/jdkdocs/api/java.lang.Throwable.html#getLocalizedMessage%28%29

https://www.cis.upenn.edu/%7Ebcpierce/courses/629/jdkdocs/api/java.lang.Throwable.html#getMessage%28%29

https://www.cis.upenn.edu/%7Ebcpierce/courses/629/jdkdocs/api/java.lang.Throwable.html#printStackTrace%28%29

https://www.cis.upenn.edu/%7Ebcpierce/courses/629/jdkdocs/api/java.lang.Throwable.html#printStackTrace%28java.io.PrintStream%29

https://www.cis.upenn.edu/%7Ebcpierce/courses/629/jdkdocs/api/java.lang.Throwable.html#printStackTrace%28java.io.PrintWriter%29

https://www.cis.upenn.edu/%7Ebcpierce/courses/629/jdkdocs/api/java.lang.Throwable.html#toString%28%29

https://www.cis.upenn.edu/%7Ebcpierce/courses/629/jdkdocs/api/java.lang.Throwable.html#printStackTrace%28%29



{

try

{



}

catch(ArithmeticExceptionexceptName)

{


}

catch(ThrowableexceptName)

{

System.out.println(“Exception!!!-TheThrowableExceptioncaughtthefollowingerror:”+“\n”);

exceptName.printStackTrace();

}

}

}

}

Figure7.19–PrintStackTraceMethod


Whatis33/2?16

Whatis55/4?13

Whatis77/6?12

Whatis99/8?12

Exception!!!-TheThrowableExceptioncaughtthefollowingerror:

java.lang.ArrayIndexOutOfBoundsException:5

atExceptionHandling.ThrowableMethod.main(ThrowableMethod.java:14)

Line21definesthesecondcatchblockwithanexceptionobject“exceptName”thatwillbeusedtodisplaytheexceptionvalueLine24createstheprintStackTrace()methodbyusingtheexceptionobjectfollowedbythedotoperator

ThrowvsThrowsThekeyword“throw”isusedtoexplicitlythrowanexception.AnobjectoftheexceptionparentclassThrowablemustbecreatedtothrowanexception.Therearetwowaystomanuallythrowanexception:

1. Useaparameterinthecatchblock2. Createanobjectusingthenewoperator

Thefollowingisthesyntaxformanually/explicitlythrowinganexception:

SyntaxthrowexcObject

Thefollowingisanexampleofthrowinganexceptionusingthenewoperator:

publicclassThrowTest

{

intDivideByZero(intnum1,intnum2)

{

if(num2==0)

{

System.out.println(“Anerrorhasnotbeenthrown”);

thrownewArithmeticException(“Exception!!!-Cannotdivideanumberbyzero”);

}

else

{

returnnum1/num2;

}

}


{

try

{

ThrowTestobjThrow=newThrowTest();

System.out.println(objThrow.DivideByZero(34,0));

}

catch(Exceptionexc)

{

System.out.println(exc.getMessage());

}

finally

{

System.out.println(“Performanactionifexceptionthrownornot“);

}

}

}

Figure7.20–ThrowExceptionExample

ProgramOutput:Anerrorhasnotbeenthrown

Exception!!!-Cannotdivideanumberbyzero

Performanactionifexceptionthrownornot

Line10createsanexplicitexceptionusingkeywords“throw”and“new”.Thekeyword“new”isusedtoconstructaninstanceof“ArithmeticException”withaStringparameter.Line24passesthevalues“34and0”tomethod“DivideByZero”whichstartsatline5.Parametervariable“num2”receiveszero“0”whichcausestheexceptionLine28displaysthestringparameterfromline10bycallingmethod“getMessage”

Thekeyword“throws”isusedtoexplicitlydefineexceptionsthatamethodmightthrow.Therefore,amethodcallmusthandlealloftheexceptionsifadeclaredmethodhasoneormoreexceptionsusingthekeyword“throws”.Thefollowingisanexampleusing“throws”todefineanexceptionlist:

SyntaxmethodTypemethodName(parameter-list)throwsexc-list{//MethodBody}

Thefollowingisanexampleusing“throws”todefineanexception:

publicclassThrowsKeywordTest

{

staticvoidthrowMethod()throwsNullPointerException

{

System.out.println(“Anerrorhasnotbeenthrown”);

thrownewNullPointerException(“Exception!!!-NullPointer”);

}


{

try

{

throwMethod();

}

catch(NullPointerExceptionexc)

{

System.out.println(“ExceptionType“+exc);

}

}

}

Figure7.21–ThrowsExceptionExample

Line5definesanexception“NullPointerException”usingthekeyword“throws”.Multipleexceptionscanbecreatedbywayofacomma-separatedlistofexceptionsthatthemethodmightthrow.Line15callsmethod“throwMethod”whichhasanexceptionLine19displaystheNullPointerException

Thefollowingdescribesthedifferencesbetweenthrowandthrows:

Throw Throws

Canthrowoneexception Candeclaremultipleexceptions

Followedbyaninstance Followedbyanexceptionclass

Usedwithinamethod’sbody Usedwithinamethod’ssignature

Figure7.22–ThrowvsThrows

DebuggingAtsomepointwhiledevelopingaprogram,theprogramwillconsistoferrorsand/orexceptions.Thekeyforeveryprogrammeristolearnhowtodebugtheprogram.Debuggingistheprocessofdetectingandremovingunexpectedconditionsfromtheprogram.AnIDEsuchasEclipseprovidesadebuggertoolwhichfacilitatethedebuggingprocess.Thetoolallowsaprogrammertoexecutetheircodeline-by-linetoviewwhatishappeningoneachline.

Breakpoints

Tostartthedebuggingprocess,abreakpointmustbeplacedintheprogram.Thepurposeofbreakpointsistopauseexecutionoftheprogram.Asaresult,theprogramrunsuptothebreakpointuntilthedebuggerreceivesadditionalinstructionsonwhattodonext.Aprogramcanhaveseveralbreakpointssetorclearedatanytime.Thefollowingisalistofwaystosetorclearabreakpoint:

1. Double-clicktheleftofthedesiredlinenumber2. Movethecursortotheleftofthedesiredlinenumber,right-clickthemouse,then

selectToggleBreakpoint3. Movethecursortothedesiredlineandpressshortcutkeys(Ctrl+Shift+B)

Abluedotislocatednexttothelinenumberaftersettingthebreakpoint.Next,theprogrammermustopentheDebugperspectivewhichprovidesacombinationofviewsandeditorstodebugaprogram.TheDebugperspectivecanbeopenedthefollowingways:

1. PressF112. Right-clickinsidetheprogram,selectDebugAs,thenJava3. ClickRunthenselectDebugAs,thenJavaApplication4. Shortcutkeys(Alt+Shift+D,J)

Note:SelectYeswhenEclipsedisplaysaConfirmPerspectiveSwitchdialogue.

Figure7.23–ConfirmPerspectiveSwitchScreenshot

ThefollowingisascreenshotoftheDebugperspective:

Figure7.24–DebugPerspectiveScreenshot

StepThroughTheProgram

Steppingthroughtheprogramiswhenthedebuggersteps/executesalineofcodeonelineatatime.Theprocessofsteppinghelpstheprogrammerunderstandhowthelogicworks.FunctionkeysF5,F6,F7,andF8controlexecutionofsteppingthroughtheprogram.

StepInto(F5)–Executesonlythecurrentcodeline.Thedebuggerpausesateverylineofcodethatissteppedintoincludingacalledmethod.StepOver(F6)–Executesthecurrentmethodwithoutdisplayingeverystep.Thedebuggerstaysinthemainroutinewhilethesubroutinesexecuteinthebackground.StepReturn(F7)–Executesthecurrentmethodinthebackgroundwhilereturningtothemethodthatwassteppedinto.Resume(F8)–Executesuntilthenextbreakpoint

Chapter7discussederrors,exceptions,anddebugging.Anerrorisaproblemintheprogram.Thethreetypesoferrorsaresyntax,runtime,andlogical.Exceptionsareerrorsthatoccuratruntime.However,anexceptionhandlerallowsablockofcodetomanagetheexceptions.Thereforetheexceptionallowsexecutiontocontinueafterrespondingtotheproblem.Debuggingisaprocessthatpermitsaprogrammertodetectandresolveallerrors.Chapter8isanintroductionJava’sinput/outputsystem.

Chapter8UtilizingInputandOutput

Java’sInput/Output(I/O)package“java.io”containsmanyclasses,interfaces,andmethods.Thepackageprovidesinputandoutputstreamsthatreads/writesdata.Dataisreadfromaninputsourceandwrittentoanoutputdestination.Aninputsourceandoutputdestinationisanythingthatcontainsinformationsuchasafile,string,ormemory.Inputisdatareceivedbytheprogramandoutputisdatasentfromtheprogram.Aprogramcanbeawebbrowserwhichreceivesandsendsdata.

ChaptereightisanintroductionwhichcoversthefollowingregardingJava’slargeInput/Outputsystem:

Streams

FileInput/Output

StreamsProgramsinJavaperforminputandoutputthroughstreams.Streamsrepresentasequenceofdatathatisreadorwritten.Thereforestreamshavetheabilitytopassdataorperformtransformationsondata.AccordingtoOracle,theInputStreamclassisanabstractsuperclassofallclassesrepresentinganinputstreamofbytes.TheOutputStreamclassisanabstractsuperclassofallclassesrepresentinganoutputstreamofbytes.ThereforetheI/Oclassesisanabstractionthatsuppliesorconsumesinformation.Streamsprovideavarietyofdataformats.

https://docs.oracle.com/javase/7/docs/api/java/io/package-summary.html#package_description

ByteStreams

BytestreamclassesarederivedfromanInputStreamandOutputStream.Programsusingbytestreamsprovidefunctionalityandmanagedetailsofreading/writing.Thefollowingisalistofbytestreamclasses.

ByteStream Description

BufferedInputStream Addsfunctionalitytoanotherinputstream-namely,theabilitytobuffertheinputandtosupportthemarkandresetmethods

BufferedOutputStream Implementsabufferedoutputstream

ByteArrayInputStream Inputstreamthatreadsfromabytearray

ByteArrayOutputStream Outputstreamthatwritestoabytearray

DataInputStream AninputstreamthatincludesmethodsforreadingtheJavastandarddatatypes

DataOutputStream AnoutputstreamthatincludesmethodsforwritingtheJavastandarddatatypes

FileInputStream Inputstreamthatreadsfromafile

FileOutputStream Outputstreamthatwritestoafile

InputStream Abstractclassthatisthesuperclassofallclassesrepresentinganinputstreamofbytes

ObjectInputStream Inputstreamforobjects

ObjectOutputStream Outputstreamforobjects

OutputStream Abstractclassthatisthesuperclassofallclassesrepresentinganoutputstreamofbytes

PipedInputStream Providesdatabytesthatarewrittentothepipedoutputstream

PipedOutputStream Connectedtoapipedinputstreamtocreateacommunicationspipe

PrintStream Outputstreamthatcontainsprint()andprintln()

PushbackInputStream Inputstreamthatallowsbytestobereturnedtothestream

SequenceInputStream Representsthelogicalconcatenationofotherinputstreams.

Figure8.1–ByteStream

ThefollowingisalistofInputStreammethods:

InputStreamMethod Description

abstractintread() Readsthenextbyteofdatafromtheinputstream

booleanmarkSupported() Testsifthisinputstreamsupportsthemarkandresetmethods

intavailable() Returnsanestimateofthenumberofbytesthatcanberead(orskippedover)fromthisinputstreamwithoutblockingbythenextinvocationofamethodforthisinputstream

intread(byte[]b) Readssomenumberofbytesfromtheinputstreamandstoresthemintothebufferarrayb

intread(byte[]b,intoff,intlen)

Readsuptolenbytesofdatafromtheinputstreamintoanarrayofbytes

longskip(longn) Skipsoveranddiscardsnbytesofdatafromthisinputstream

voidclose() Closesthisinputstreamandreleasesanysystemresourcesassociatedwiththestream

voidmark(intreadLimit) Marksthecurrentpositioninthisinputstream

voidreset() Repositionsthisstreamtothepositionatthetimethemarkmethodwaslastcalledonthisinputstream

Figure8.2–InputStreamMethods

ThefollowingisalistofOutputStreammethods:

OutputStreamMethods

Description

abstractvoidwrite(intb)

Writesthespecifiedbytetothisoutputstream

voidclose() Closesthisoutputstreamandreleasesanysystemresourcesassociatedwiththisstream

voidflush() Flushesthisoutputstreamandforcesanybufferedoutputbytestobewrittenout

voidwrite(byte[]b) Writesb.lengthbytesfromthespecifiedbytearraytothisoutputstream

voidwrite(byte[]b,intoff,intlen)

Writeslenbytesfromthespecifiedbytearraystartingatoffsetofftothisoutputstream

Figure8.3–OutputStreamMethods

CharacterStream

CharacterstreamclassesarederivedfromReaderandWriterwhichoffersimilarmethodsasInputStreamandOutputStream.ThecharacterstreamclassmanagesI/Oparallelingthebytestreamclass.Unicodecharactersaretranslatedfromcharacterstreamclasses.Thefollowingisalistofcharacterstreamclasses:

CharacterStream Description

BufferedReader Readstextfromacharacter-inputstream,bufferingcharacterssoastoprovidefortheefficientreadingofcharacters,arrays,andlines.

BufferedWriter Writestexttoacharacter-outputstream,bufferingcharacterssoastoprovidefortheefficientwritingofsinglecharacters,arrays,andstrings.

CharArrayReader Thisclassimplementsacharacterbufferthatcanbeusedasacharacter-inputstream.

CharArrayWriter ThisclassimplementsacharacterbufferthatcanbeusedasanWriter.

FileReader Convenienceclassforreadingcharacterfiles.

FileWriter Convenienceclassforwritingcharacterfiles.

FilterReader Abstractclassforreadingfilteredcharacterstreams

FilterWriter Abstractclassforwritingfilteredcharacterstreams

InputStreamReader AnInputStreamReaderisabridgefrombytestreamstocharacterstreams:Itreadsbytesanddecodesthemintocharactersusingaspecifiedcharset

LineNumberReader Abufferedcharacter-inputstreamthatkeepstrackoflinenumbers

OutputStreamWriter AnOutputStreamWriterisabridgefromcharacterstreamstobytestreams:Characterswrittentoitareencodedintobytesusinga

specifiedcharset

PipedReader Pipedcharacter-inputstreams

PipedWriter Pipedcharacter-outputstreams.

PrintWriter Printsformattedrepresentationsofobjectstoatext-outputstream.

PushbackReader Acharacter-streamreaderthatallowscharacterstobepushedbackintothestream.

Reader Abstractclassforreadingcharacterstreams

StringReader Acharacterstreamwhosesourceisastring.

StringWriter Acharacterstreamthatcollectsitsoutputinastringbuffer,whichcanthenbeusedtoconstructastring

Writer Abstractclassforwritingtocharacterstreams

Figure8.4–CharacterStream

BufferedStreams

Bufferedinputstreamsreaddatafromamemoryareaknownasabuffer.Ontheotherhand,bufferedoutputstreamswritedatatoabuffer.InJava,majorityofthestreamsareunbufferedmeaningeachreadorwriterequestismanageddirectlybytheoperatingsystem(OS).AmanagementrequestbyanOSmakeprogramslessefficientduetoarequesttriggeringanexpensiveoperation.

BufferedI/Ostreamsisimplementedtoreduceoverheadbyadministeringadedicatedspaceinmemory.Thededicatedspacestoresdatainanefficientmanner.Forinstance,thebufferedinputstreamisonlycalledwhenthebufferisemptyandbufferedoutputstreamsareonlycalledwhenthebufferisfull.Therefore,thefourfollowingbufferclassescanbeusedtowraparoundabyteorcharacterI/Ostream:

BufferClasses Description

BufferedInputStream Suppliesbufferingtooutputstreams

BufferedOutputStream Suppliesbufferingtoinputstreams

BufferedReader Readstextfromacharacterinputstream

BufferedWriter Writestexttoacharacteroutputstream

Figure8.5–BufferedStreams

DataStreams

DatastreamsserveasafoundationforStringvalues,binaryinput,andoutputofprimitivedatatypessuchasboolean,byte,char,double,float,int,long,andshort.ADataInputorDataOutputinterfaceisimplementedbyallofthedatastreams.TheDataInputinterfaceprovidesmethodsforreadingwhileDataOutputinterfaceprovidesmethodsforwritingallofJava’sprimitivetypes.DataInputStreamimplementstheDataInputinterfaceandDataOutputStreamimplementstheDataOutputinterface.ThefollowingisalistofmethodsforDataInputStreamandDataOutputStream:

DataInputStreamMethod Description

booleanreadBoolean() Readsabooleaninputfromthefile

bytereadByte() Readsabyteinputfromthefile

charreadChar() Readsacharinputfromthefile

doublereadDouble() Readsadoubleinputfromthefile

floatreadFloat() Readsafloatinputfromthefile

intreadInt() Readsaintinputfromthefile

longreadLong() Readsalonginputfromthefile

shortreadShort() Readsashortinputfromthefile

Figure8.6–DataInputStreamMethods

DataOutputStreamMethod

Description

voidwriteBoolean(booleanv)

Writesabooleanoutputtothefile

voidwriteByte(intv) Writesabyteoutputtothefile

voidwriteChar(intv) Writesacharoutputtothefile

voidwriteDouble(doublev) Writesadoubleoutputtothefile

voidwriteFloat(floatv) Writesafloatoutputtothefile

voidwriteInt(intv) Writesaintoutputtothefile

voidwriteLong(longv) Writesalongoutputtothefile

voidwriteShort(intv) Writesashortoutputtothefile

Figure8.7–DataOutputStreamMethods

StandardStreams

JavaprovidessupportforstandardI/Osoaprogramreceivesinputfromakeyboardandproduceoutputontothecomputermonitor.AclasscalledSystemwithinthejava.langpackageincludesthreestandardstreamvariables:in,out,anderr.System.inisanInputStreamobjectwhileSystem.outandSystem.errarePrintStreamobjects.PrintStreamallowsformatteddatatobewrittentoanOutputStream.Thefollowingisadescriptionofthestandardstreams:

StandardStream Description

StandardInput (System.in)/BydefaultthekeyboardStandardInputcontrolswheretheprogramreceivesinput

StandardOutput (System.out)/BydefaulttheconsoleStandardOutputcontrolswheretheprogramsendsoutput

StandardError (System.err)/BydefaulttheconsoleStandardErrorusedtooutputanerrorsuppliedbytheprogram

Figure8.8–StandardStreams

FileInput/OutputFilesarestoredandorganizedsotheycanberetrievedandaccessedinaconvenientmanner.InJava,therearetwopackages“java.io.fileandjava.nio.fio”setasideforfiles.Package“java.nio.file”isthenewerfilesystemlabeledNIO2meaning“NewInput/Output2”.NIO2identifiesinterfacesandclassestoaccessfiles,fileattributes,andfilesystems.

Path

Mostfilesarearrangedinahierarchical(knownastree)structure.Therootnode(i.e.,C:\)islocatedatthetopofthehierarchyfollowedbyfoldersandfiles.Allfoldershavetheabilitytoincludeadditionalfoldersandfiles.Auniquepathidentifiesaspecificresource(fileorfolder)withinatree.Thereforethepath“C:\java4selenium\input_output\test.txt”indicatesafilenamed“test”islocatedinafoldernamed“input_output”withinanotherfoldernamed“java4selenium”.ThefollowingarecommonPathInterfacemethodsforJava’sfilesystem:

PathConversion

toAbsolutePath()ReturnsaPathobjectcharacterizingtheabsolutepathtoRealPath(LinkOption…options)ReturnstherealpathofanexistingfiletoUri()ReturnsaURItocharacterizethispath

RetrievePathInformation

getFileName()ReturnsthenameofthefileorlastelementinthePathobjectgetName(intindex)ReturnsthePathelementcorrespondingtothespecifiedindexgetNameCount()ReturnsthenumberofnameelementsinthepathgetParent()ReturnstheparentpathornullgetRoot()Returnsthepath’srootnormalize()Returnsapathwithredundantnameelementseliminated

resolve(Pathother)Resolvethespecifiedpathagainstthispathrelativize(Pathother)ConstructsarelativepathbetweenthispathandaspecifiedpathsubPath(intbeginIndex,intendIndex)ReturnsthesubsequenceofthePathindicatedbystartingandendingindicestoStringReturnsthepath’sstringrepresentation

Files

Filescanbecreated,deleted,moved,copied,andverifiedforexistence.Bothpackages“java.io.fileandjava.nio.fio”includemethodswhichread,write,andmanipulatefilesandfolders.ThefollowingarecommonmethodswithinbothpackagesforJava’sfilesystem:

CheckExistenceMethods

exists(Pathpath,LinkOption…options)TestsiftheresourceexistnotExists(Pathpath,LinkOption…options)Testsiftheresourcelocatedbythispathdoesnotexist

CheckStatusMethods

isDirectory(Pathpath,LinkOption…options)TestsiftheresourceisadirectoryisExecutable(Pathpath)TestsiftheresourceisexecutableisFile()TestsiftheresourceindicatedbythisabstractpathnameisanormalresourceisReadable(Pathpath)TestsiftheresourceisreadableisSameFile(Pathpath,Pathpath2)TestsiftworesourceslocatethesameresourceisWritable(Pathpath)Testsiftheresourceiswritable

CopyMethod

copy(Pathsource,Pathtarget,CopyOption…options)Copytheresourcetoaspecifiedtarget

https://docs.oracle.com/javase/7/docs/api/java/nio/file/Files.html#exists%28java.nio.file.Path,%20java.nio.file.LinkOption…%29

https://docs.oracle.com/javase/7/docs/api/java/nio/file/Path.html

https://docs.oracle.com/javase/7/docs/api/java/nio/file/LinkOption.html

https://docs.oracle.com/javase/7/docs/api/java/nio/file/Files.html#notExists%28java.nio.file.Path,%20java.nio.file.LinkOption…%29


https://docs.oracle.com/javase/7/docs/api/java/nio/file/LinkOption.html

CreateMethod

createFile(Pathpath,FileAttribute<?>…attrs)Createsanewandemptyresource

DeleteMethod

Delete(Pathpath)Deletestheresource

Note:Foldersmustbeemptybeforeitcanbedeleted

DirectoryMethods

list()ReturnsanarrayofstringsnamingtheresourcesanddirectoriesinthedirectoryindicatedbythisabstractpathnamelistFiles()Returnsanarrayofabstractpathnamesindicatingthefilesinthedirectoryindicatedbythisabstractpathname

MoveMethod

move(Pathsource,Pathtarget,CopyOption…options)Moveorrenametheresourcetoatarget

ReadMethods

readAllBytes(Pathpath)ReadsallthebytesfromtheresourcereadAllLines(Pathpath,Charsetcs)Readalllinesfromtheresource

https://docs.oracle.com/javase/7/docs/api/java/nio/file/Files.html#move%28java.nio.file.Path,%20java.nio.file.Path,%20java.nio.file.CopyOption…%29



https://docs.oracle.com/javase/7/docs/api/java/nio/file/CopyOption.html

SpaceMethods

length()ReturnsthelengthoftheresourceindicatedbythisabstractpathnamegetFreeSpace()ReturnsthenumberofunallocatedbytesinthepartitionnamedbythisabstractpathnamegetTotalSpace()ReturnsthesizeofthepartitionnamedbythisabstractpathnamegetUsableSpace()Returnsthenumberofbytesavailabletothisvirtualmachineonthepartitionnamedbythisabstractpathname

WriteMethods

write(Pathpath,byte[]bytes,OpenOption…options)Writesbytestotheresourcewrite(Pathpath,Iterable<?extendsCharSequence>linesCharsetcs,OpenOption…options)Writelinesoftexttotheresource

ConclusionJavaisapopularobject-orientedprogramming(OOP)languagecenteredaroundobjects.Thegoalof“Part2–Java4SeleniumWebDriver”wastoprovidedeepconceptsofJava.OneofthebenefitsofJavaistheabilitytoreusecode.Thefollowingaretake-awaytopicsfromthisbook:

Classes:Aclassisatemplateforobjectswhichcontainsdataandcodethatoperatesonthedata.

Objects:Objectsarethefoundationtoobject-orientedprogramming.Itconsistsoftwocharacteristics:stateandbehavior.Stateidentifiestheobjectandbehaviorrepresenttheactionsoftheobject.

Methods:Amethodisablockofcodethatperformaspecifictask.

Inheritance:Inheritanceisahierarchicalconceptwhichallowsreusablecodeandobjectstobeextended.

Package:Apackageisacollectionofrelatedclasses.

Interface:Aninterfaceisacollectionofrelatedmethods.

Error:Anerrorisanunavoidableprobleminaprogram.

Exceptions:Anexceptionisanerrorthatoccursatruntime

Debugging:Debuggingistheprocessofdetectingandremovingunexpectedconditionsfromtheprogram.

Resources1.BeginningJava®ProgrammingTheObject-OrientedApproachBartBaesens,AiméeBackiel,SeppevandenBroucke

2.JavaABeginner’sGuideSixthEditionCreate,Compile,andRunJavaProgramsTodayHerbertSchildt

3.ORACLEJavaDocumentationTheJavaTMTutorialshttps://docs.oracle.com/javase/tutorial/java/javaOO/returnvalue.htmlhttps://docs.oracle.com/javase/7/docs/api/https://docs.oracle.com/javase/7/docs/api/java/io/package-summary.html#package_description

4.ProgramCreekhttp://www.programcreek.com/2009/02/diagram-for-hierarchy-of-exception-classes/

5.TIOBEhttp://www.tiobe.com/tiobe_index

6.Dictionary.comhttp://www.dictionary.com/browse/object?s=thttp://www.dictionary.com/browse/annotation?s=t

https://docs.oracle.com/javase/tutorial/java/javaOO/returnvalue.html

https://docs.oracle.com/javase/7/docs/api/

https://docs.oracle.com/javase/7/docs/api/java/io/package-summary.html#package_description

http://www.programcreek.com/2009/02/diagram-for-hierarchy-of-exception-classes/

http://www.tiobe.com/tiobe_index

http://www.dictionary.com/browse/object?s=t

http://www.dictionary.com/browse/annotation?s=t

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