MobileDevelopmentWorkshopDAY1: INTRODUCTIONTOJAVA

OverviewMorningsession◦ Computerhardware,software,andprogramming languages◦ TheJavaprogramming language◦ Simple Javastatements◦ Data,variables,andtypes◦ Classes,objects,andmethods

Afternoonsession◦ Controlflow◦ Conditional statements◦ Loops

HardwareandSoftwareComputersystemsconsistofhardware andsoftware.◦ Hardwareincludesthetangible partsofcomputersystems.◦ Softwareincludesprograms - setsofinstructionsforthecomputertofollow.

Familiaritywithhardwarebasicshelpsusunderstandsoftware.

MemoryMemoryholds◦ programs◦ dataforthecomputer toprocess◦ theresultsof intermediateprocessing.

Twokindsofmemory◦ mainmemory◦ auxiliarymemory

Bits,Bytes,andAddressesAbit isadigitwithavalueofeither0or1.Abyte consistsof8bits.Eachbyteinmainmemoryresidesatanumberedlocationcalleditsaddress.

MainMemoryFigure1.1

ProgramsAprogram isasetofinstructionsforacomputertofollow.Weuseprogramsalmostdaily(email,wordprocessors,videogames,bankATMs,etc.).Followingtheinstructionsiscalledrunning orexecuting theprogram.

RunningaProgram

ProgrammingLanguagesHigh-level languagesarerelativelyeasytouse◦ Java,C#,C++,VisualBasic,Python,Ruby.

Unfortunately,computerhardwaredoesnotunderstandhigh-levellanguages.◦ Therefore,ahigh-levellanguageprogrammustbetranslatedintoalow-levellanguage.

CompilersAcompilertranslatesaprogramfromahigh-levellanguagetoalow-levellanguagethecomputercanrun.Youcompile aprogrambyrunningthecompileronthehigh-level-languageversionoftheprogramcalledthesourceprogram.Compilersproducemachine- or assembly-languageprogramscalledobjectprograms.

JavaByte-CodeTheJavacompiler doesnottranslateaJavaprogramintoassemblylanguage ormachinelanguage foraparticularcomputer.Instead,ittranslatesaJavaprogramintobyte-code.◦ Byte-codeisthemachinelanguage forahypotheticalcomputer(or interpreter)calledtheJavaVirtualMachine.

CompilingandRunningaProgram

WritingourfirstJavaProgramsWriteaprogramthatoperateslikethis:

Samplescreenoutput

PrintingtothescreenSystem.out.println (“Whatever you want to print”);

System.out isanobjectforsendingoutputtothescreen.println isamethodtoprintwhateverisinparenthesestothescreen.

PrintingtothescreenThe object performs an action when you invoke or call one of its methodsobjectName.methodName(argumentsTheMethodNeeds);

Object-OrientedProgrammingOurworldconsistsofobjects (people,trees,cars,cities,airlinereservations,etc.).

Objectscanperformactionswhichaffectthemselvesandotherobjectsintheworld.

Object-orientedprogramming(OOP)treatsaprogramasacollectionofobjectsthatinteractbymeansofactions.

OOPTerminologyObjects,appropriately,arecalledobjects.Actions arecalledmethods.Objectsofthesamekindhavethesametype andbelongtothesameclass.◦ Objectswithinaclasshaveacommonsetofmethodsandthesamekindsofdata

◦ buteachobjectcanhaveit’sowndatavalues.

OOPDesignPrinciplesOOPadherestothreeprimarydesignprinciples:◦ Encapsulation◦ Polymorphism◦ Inheritance

IntroductiontoEncapsulationThedataandmethodsassociatedwithanyparticularclassareencapsulated(“puttogetherinacapsule”),butonlypartofthecontentsismadeaccessible.◦ Encapsulationprovidesameansofusingtheclass,butitomitsthedetailsofhowtheclassworks.

◦ Encapsulationofteniscalledinformationhiding.

ExampleAnautomobileconsistsofseveralpartsandpiecesandiscapableofdoingmanyusefulthings.◦ Awarenessoftheacceleratorpedal,thebrakepedal,andthesteeringwheelisimportanttothedriver.

◦ Awarenessofthefuelinjectors,theautomaticbrakingcontrolsystem,andthepowersteeringpumpisnotimportanttothedriver.

IntroductiontoInheritanceClassescanbeorganizedusinginheritance.

Aclassatlowerlevelsinheritsallthecharacteristicsofclassesaboveitinthehierarchy.

Ateachlevel,classificationsbecomemorespecializedbyaddingothercharacteristics.

Higherclassesaremoreinclusive;lowerclassesarelessinclusive.

IntroductiontoInheritance

VariablesVariables storedatasuchasnumbersandletters.◦ Thinkofthemasplacestostoredata.◦ Theyareimplementedasmemorylocations.

Thedatastoredbyavariableiscalleditsvalue.◦ Thevalueisstoredinthememorylocation.

Itsvaluecanbechanged.

NamingandDeclaringVariablesChoosenamesthatarehelpfulsuchascount orspeed,butnotc ors.

Whenyoudeclare avariable,youprovideitsnameandtype.

int heightInCentimeters,age;

Avariable'stype determineswhatkindsofvaluesitcanhold(int, double, char, etc.).

Avariablemustbedeclaredbeforeitisused.

DataTypesAclasstype isusedforaclassofobjectsandhasbothdataandmethods.◦ "Java is fun" isavalueofclasstypeString

Aprimitivetype isusedforsimple,nondecomposablevaluessuchasanindividualnumberorindividualcharacter.◦ int, double, andchar areprimitivetypes.

PrimitiveTypes

PrimitiveTypesFourintegertypes(byte, short, int, andlong)◦ int ismostcommon

Twofloating-pointtypes(float anddouble)◦ double ismorecommon

Onecharactertype(char)Onebooleantype(boolean)

ExamplesofPrimitiveValuesIntegertypes

0 -1 365 12000

Floating-pointtypes0.99 -22.8 3.14159 5.0

Charactertype'a' 'A' '#' ' '

Booleantypetrue false

AssignmentStatementsAnassignmentstatementisusedtoassignavaluetoavariable.answer = 42;

The"equalsign"iscalledtheassignmentoperator.Wesay,"Thevariablenamedanswer isassignedavalueof42,"ormoresimply,"answer isassigned42."

AssignmentExamplesamount = 3.99;

firstInitial = 'W';

birthYear = currentYear - age;

total = total + 2;

AssignmentCompatibilitiesJavaissaidtobestronglytyped.◦ Youcan't,forexample,assignafloatingpointvaluetoavariabledeclaredtostoreaninteger.

Sometimesconversionsbetweennumbersarepossible.doubleVariable = 7;

ispossibleevenifdoubleVariable isoftypedouble,forexample.

ArithmeticOperatorsArithmeticexpressionscanbeformedusingthe+, -, *, and/operatorstogetherwithvariablesornumbersreferredtoasoperands.◦ Whenbothoperandsareofthesametype,theresultisofthattype.◦ Whenoneoftheoperandsisafloating-pointtypeandtheotherisaninteger,theresultisafloatingpointtype.

ArithmeticOperatorsExample

IfhoursWorked isanint towhichthevalue40 hasbeenassigned,andpayRate isadouble towhich8.25 hasbeenassigned

hoursWorked * payRate

isadouble withavalueof500.0.

TheDivisionOperatorThedivisionoperator(/)behavesasexpectedifoneoftheoperandsisafloating-pointtype.Whenbothoperandsareintegertypes,theresultistruncated,notrounded.◦ Hence,99/100hasavalueof0.

Themod OperatorThemod (%)operatorisusedwithoperatorsofintegertypetoobtaintheremainderafterintegerdivision.14dividedby4is3witharemainderof2.◦ Hence,14 % 4 isequalto2.

Themodoperatorhasmanyuses,including◦ determiningifanintegerisoddoreven◦ determiningifoneintegerisevenlydivisiblebyanotherinteger.

SampleExpressions

TheClassStringWe'veusedconstantsoftypeString already."Enter a whole number from 1 to 99."

AvalueoftypeString isa◦ Sequenceofcharacters◦ Treatedasasingleitem.

ConcatenationofStringsTwostringsareconcatenated usingthe+ operator.String greeting = "Hello";String sentence;sentence = greeting + " madam";System.out.println(sentence);

Anynumberofstringscanbeconcatenatedusingthe+ operator.

ClassandMethodDefinitions

ClassandMethodDefinitions

Objects that are instantiations of the

class Automobile

MethodsWhenyouuseamethodyou"invoke"or"call"itTwokindsofJavamethods◦ Returnasingleitem◦ Performsomeotheraction– avoid method

Themethodmain isavoidmethod◦ Invokedbythesystem◦ Notbytheapplicationprogram