Introductionevcomp.dcc.ufmg.br/wp-content/uploads/Kotlin-Intro.pdf · 1. Supercell: The Finnish...

Introduction

[email protected]

IsitprofitabletodevelopApps?

- Intheworld?- InBrazil?- Successstories?

1. Supercell:TheFinnishmobilegamepublisherisarounda$3billioncompany.MostfamousforitsgameClashofClans.

2. King:TheCandyCrushlegendisstillgeneratingalotofmoney.Kinggeneratedmorethan$1.9billionin2013.

3. GungHoOnline:Puzzle&Dragons,broughtin$650millionthroughApple'sAppStoreand$775millionthroughGooglePlayin2013.

Whatwerethemostdownloadedappsin2019?

And,whataboutinBrazil?

And,whataboutinBrazil?

Lista do Google dos melhores apps em 2018 tem 2 brasileiroshttps://noticias.uol.com.br/tecnologia/noticias/redacao/2018/12/03/baixou-lista-do-google-dos-melhores-apps-em-2018-tem-2-brasileiros-veja.htm HeltonSimõesGomes,12-03-2018

GuiaBolso Filmr

https://tecnologia.uol.com.br/noticias/redacao/2018/11/08/dobra-n-de-apps-que-ganham-r-1-mi-no-brasil-qual-a-receita-do-sucesso.htm

https://www.correiobraziliense.com.br/app/noticia/tecnologia/2015/05/11/interna_tecnologia,482694/brasil-decola-na-industria-de-apps-e-mercado-acumula-lucros-nesta-deca.shtml

https://istoe.com.br/194216_OS+MILIONARIOS+DOS+APLICATIVOS/

Appsareimplementedinwhichprogramminglanguages?

Appsareimplementedinwhichprogramminglanguages?

- Non-nativesupport- C#- Python- JavaScript- Php- Lua- ...

- Nativesupport- Java- Dart- C++[*]- Kotlin

*:wecan'tdeveloptheentireappinC++

Whycan'twesimplystaywithJava?

- WhenwasJavacreated?

- WhatwouldyouliketochangeinJava?


- Verbosity- NoREPL- Poorsupporttofunctionalprogramming


Verbosity

- NoREPLPoorsupporttofunctionalprogramming

What'sthat?


Verbosity

- NoREPL- Canyounameeachprogramminglanguagebelow?

Poorsupporttofunctionalprogramming

>>>2+24>>>

- 2+2;valit=4:int-

?-Xis2+2.X=4.?-

#2+2;;;- :int=4#

Andwhat'sKotlin?

- Whenwasitcreated?

- Whocreatedit?- Howdoesitlooklike?- HowcanwerunKotlinprograms?- Howcanweinstallit?

Installing(Linux)

SDKMan

$curl-shttps://get.sdkman.io|bash$sdkinstallkotlin

Snap

$sudosnapinstall--classickotlin

Installing(OSX)

Homebrew

$brewupdate$brewinstallkotlin

MacPorts

$sudoportinstallkotlin

Installing(IDE)

HowcanwerunKotlinprograms?

HowcanwerunKotlinprograms?

funmain(args:Array<String>){println("Hello,World!")}

$kotlinchello.kt-include-runtime-dhello.jar$java-jarhello.jar

REPL

$kotlincWelcometoKotlinversion1.2.31(JRE1.8.0_65-b17)Type:helpforhelp,:quitforquit

>>>println("Hello,World!")Hello,World!

>>>2+24

Scripting

importjava.io.Filevalfolders=File(args[0]).listFiles{file->file.isDirectory()}folders?.forEach{folder->println(folder)}

$kotlinc-scriptlist_folders.kts..../FreqCounter../Scripts../Tests

list_folders.kts

Example:PointReader.kt

Implementaprogramthatreadsacsvfilecontainingalistof2Dpoints,andprintstheXcoordinateofeachpoint.

$cat~/Desktop/inst.csvX,Y2,3-1,4-2,-10,31,2

Example of input

- Howmanyloopsdoyouneed?

- Howmanylinesofcode?


- Wherearethetypes?

- Wherearetheloops?- Howtocompileandrunit?

importjava.io.Filefunmain(args:Array<String>){valfile=File(args[0])vallines=file.readLines().drop(1)valxList=lines.map{it.split(",").get(0).toFloat()}xList.forEach{println(it)}}

PointReader.kt



PointReader.kt

$kotlincPointReader.kt-include-runtime-dpointReader.jar$java-jarpointReader.jar~/Desktop/inst.csv2.0-1.0-2.00.01.0


- L4:what'sdrop(1)doing?Whydoweuseit?

- L5:what'smap?- L5:what's'it'init.split(",")?- L5:what'ssplit(",")?


PointReader.kt

1234567

DEPARTMENTOFCOMPUTERSCIENCEUNIVERSIDADEFEDERALDEMINASGERAIS

FEDERALUNIVERSITYOFMINASGERAIS,BRAZIL

BASICSINTAX

Whatareprimitivetypes?

- WhataretheprimitivetypesinC?

- WhataboutJava?

PrimitiveTypesinC

- char- short- int- long- longlong- float- double- longdouble

- scalartypes- signed- unsigned- int

signedlonglongx0=10;signedlonglongx1int=10;unsignedshort=10;unsignedshortint=10;

PrimitiveTypesinJava

- Integers- byte- chart- short- int- long

- Floatingpoints- float- double

- boolean

PrimitiveTypesinKotlin

- Integers- Byte- Short- Int- Long

- Floatingpoints- Float- Double

Canyouexplaineacherrorthatwegot?

>>>vali:Int=2>>>valb:Byte=8>>>valb:Byte=129error:...

>>>vald:Double=129.0>>>vald:Double=129error:...

>>>vald:Double=129.toDouble()

- Integers- Byte- Short- Int- Long

- Floatingpoints- Float- Double

Typeconversionsmustbeexplicit

intn1=42;longn2=n1;

Java

Kotlin

>>>valn1:Int=42>>>valn2:long=n1error:...>>>valn2:Long=n1.toLong()

- toByte()- toShort()- toInt()- toLong()- toFloat()- toDouble()- toChar()

Whymakingconversionsexplicit?

Kotlin

>>>valn1:Int=42>>>valn2:long=n1error:...>>>valn2:Long=n1.toLong()

- Advantages?- Disadvantages?- Otherprogramminglanguages?

InferencevsTypeAnnotations

importjava.io.Filefunmain(args:Array<String>){valpFile=File(args[0])vallines=pFile.readLines()valpOnly=lines.drop(1)valpList=pOnly.map{it.split(",")}valxStrs=pList.map{it.get(0)}valxList=xStrs.map{it.toFloat()}xList.forEach{println(it)}}

PointReader.kt

- Canyouguesseachtype?


importjava.io.Filefunmain(args:Array<String>){valpFile:File=File(args[0])vallines:List<String>=pFile.readLines()valpOnly:List<String>=lines.drop(1)valpList:List<List<String>>=pOnly.map{it.split(",")}valxStrs:List<String>=pList.map{it.get(0)}valxList:List<Float>=xStrs.map{it.toFloat()}xList.forEach{println(it)}}

PointReader.kt

- What'stheadvantageofusingtypeinference?

- What'stheadvantageofusingannotations?



LISTSANDRANGES

importjava.io.Filefunmain(args:Array<String>){valpFile:File=File(args[0])vallines:List<String>=pFile.readLines()valpOnly:List<String>=lines.drop(1)valpList:List<List<String>>=pOnly.map{it.split(",")}valxStrs:List<String>=pList.map{it.get(0)}valxList:List<Float>=xStrs.map{it.toFloat()}xList.forEach{println(it)}}

PointReader.kt

WhichoperationswouldyouexpecttofindinLists?

BasicListOperations

>>>valitems=listOf(1,2,3,4)>>>items.first()1>>>items.last()4>>>items.drop(1)[2,3,4]>>>items.contains(2)true>>>items.get(2)3>>>items.indexOf(2)1>>>items.subList(1,3)[2,3]>>>items.dropLast(2)[1,2]

Rangesareasimplewaytobuildlistsanditerators

>>>valr=1..10>>>r1..10>>>r.first()1>>>r.last()10>>>r.toList()[1,2,3,4,5,6,7,8,9,10]>>>r.drop(1)[2,3,4,5,6,7,8,9,10]>>>r.contains(2)true>>>r.indexOf(3)2

ListsandRangesgivesusControlStructures

>>>if(2in1..10){println("oi")}oi>>>for(iin1..4)println(i)1234>>>for(iinlistOf("a","b","cd","efg"))...println(i)abcdefg

High-OrderFunction:map

- Whatisx -> x * x ?

- Andwhatisx -> x.toString() + "!" ?

>>>valitems=listOf(2,3,5,7,11,13)>>>items.map{x->x*x}[4,9,25,49,121,169]>>>items.map{x->x.toString()+"!"}[2!,3!,5!,7!,11!,13!]

LambdaExpressions

>>>valf={a:Int,b:Int->a+b}>>>f(2,3)5

>>>valg={a:Float,b:Float,c:Float->a*b+c}>>>g(2.76F,3.14F,1.12F)9.7864

>>>valitems=listOf(2,3,5,7,11,13)>>>items.map{x->x*x}[4,9,25,49,121,169]

AnonymousFunctions

>>>valh=fun(L:List<Int>,e:Int,d:Int):Int{...valaux=L.indexOf(e)...returnif(aux>-1)eelsed...}

>>>h(listOf(1,2,3),2,10)2

>>>h(listOf(1,2,3),4,10)10

- What'sthedifferencebetweenusinganonymousfunctions(withthefunkeyword)andlambdablocks?

- Couldyourewritethesamefunctionh,thistimeasalambdaexpression?

LambdaExpressionsareAnonymousFunctions

>>>valh={L:List<Int>,e:Int,d:Int->if(L.indexOf(e)>-1)eelsed}

>>>h(listOf(1,2,3),2,10)2

>>>h(listOf(1,2,3),4,10)10

- Whenisitmandatorytouseanonymousfunctions?

What'sthetypeofeachLXandEX?

>>>valitems=listOf(2,3,5,7)

>>>valL0=items.map{x->kotlin.math.ln(x.toDouble())}>>>L0.javaClass???>>>valE0=L0.first()>>>E0.javaClass???

>>>valL1=items.map{x->x>4}>>>valE1=L1.first()>>>E1.javaClass???

>>>valL2=items.map{x->listOf(x)}>>>valE2=L2.first()>>>E2.first().javaClass???

What'sthetypeofeachLXandEX?

>>>valitems=listOf(2,3,5,7)

>>>valL0=items.map{x->kotlin.math.ln(x.toDouble())}>>>L0.javaClassclassjava.util.ArrayList>>>valE0=L0.first()>>>E0.javaClassdouble

>>>valL1=items.map{x->x>4}>>>valE1=L1.first()>>>E1.javaClassboolean

>>>valL2=items.map{x->listOf(x)}>>>valE2=L2.first()>>>E2.first().javaClassclassjava.util.Collections$SingletonList

Thesingleparameterit

- Whencanweuseit?

>>>items.map{kotlin.math.ln(it.toDouble())}[0.69,1.10,1.61,1.94]

>>>items.map{it>4}[false,false,true,true]

>>>items.map{listOf(it)}[[2],[3],[5],[7]]

forvsforEach

- What'sthecodeabovedoing?

>>>vallist=(1..1000).toList()

- Andthisprogramabove,what'sitdoing?

>>>varx:Int=0>>>kotlin.system.measureNanoTime{for(iinlist){x+=i}}469793

- Finally,whatistheforEachdoinginthecodeabove?- Whichoneisfaster,forEachorfor,forlists?

>>>varx:Int=0>>>kotlin.system.measureNanoTime{list.forEach{x+=it}}397783


importjava.io.Filefunmain(args:Array<String>){valpFile=File(args[0])vallines=pFile.readLines()valpOnly=lines.drop(1)valpList=pOnly.map{it.split(",")}valxStrs=pList.map{it.get(0)}valxList=xStrs.map{it.toFloat()}xList.forEach{println(it)}}

PointReader.kt

- Canyouexplainnowwhatisdoingeachlineabove?

3456789

High-OrderFunction:fold

- Whatisfoldgoodfor?

>>>listOf(1,2,3).fold(0){acc,element->acc+element}6

>>>listOf("a","b","c").fold(""){acc,element->acc+element}abc

>>>listOf(true,false,true).fold(0){x,e->if(e)x+1elsex}2

Fillupthequestionmarks

>>>valL=listOf(2,3,5,7,11)>>>L.fold(0){x,e->if(e>x)eelsex}??

>>>(L.fold(0){x,e->x+e})/L.size??

Fillupthequestionmarks

- What'sthisweirdsyntax:L.fold(0){x,e->x+e}?

>>>valL=listOf(2,3,5,7,11)>>>L.fold(0){x,e->if(e>x)eelsex}11

>>>(L.fold(0){x,e->x+e})/L.size5

TheLastParameter

- Ifthelastparameterisafunction,thenitcanbepassedoutsideparentheses.

>>>L.fold(0){x,e->x+e}28

>>>L.fold(0,{x,e->x+e})28

Usingreduce insteadoffold.

>>>L.reduce{x,e->if(e>x)eelsex}11

>>>L.reduce{x,e->if(e<x)eelsex}2

- What'sthedifferencebetweenfold andreduce?

- Whatwillhappenintheprogrambelow?

emptyList<Int>().reduce{x,e->if(e<x)eelsex}

Example:Centroid.kt

Implementaprogramthatreadsacsvfilecontainingalistof2Dpoints,andprintsthecentroidofthesepoints.

$cat~/Desktop/inst.csvX,Y3,30,4-1,-21,32,2

Example of input

- What'sacentroid?

- Whichoperationswillweneed?

Example:Centroid.kt

- Whatisthemeaningof${xAvg}, ${yAvg}?- Canyouthinkonwaysofimprovingthis

program?

importjava.io.Filefunmain(args:Array<String>){valfile=File(args[0])vallines=file.readLines()valpoints=lines.drop(1)valxL=points.map{it.split(",").get(0).toFloat()}valxAvg=xL.fold(.0){x,e->x+e}/xL.size.toFloat()valyL=points.map{it.split(",").get(1).toFloat()}valyAvg=yL.fold(.0){x,e->x+e}/yL.size.toFloat()print("Centroid=(${xAvg},${yAvg})")}

Centroid.kt

Externalfunction

- Shouldwemovelines9and11towithinavg?

importjava.io.Filefunavg(list:List<Float>):Float{ returnlist.fold(.0F){x,e->x+e}/list.size.toFloat()}funmain(args:Array<String>){ valfile=File(args[0]) vallines=file.readLines() valpoints=lines.drop(1) valxList=points.map{it.split(",").get(0).toFloat()} valxAvg=avg(xList) valyList=points.map{it.split(",").get(1).toFloat()} valyAvg=avg(yList) print("Centroid=(${xAvg},${yAvg})")}

Centroid2.kt

123456789

10111213

Externalfunction

- Whichfunctionismorereusable,avgoravg2?

importjava.io.Filefunavg2(list:List<String>,index:Int):Float{ valfList=list.map{it.split(",").get(index).toFloat()} returnfList.fold(.0F){x,e->x+e}/fList.size.toFloat()}funmain(args:Array<String>){ valfile=File(args[0]) vallines=file.readLines() valpoints=lines.drop(1) valxAvg=avg2(points,0) valyAvg=avg2(points,1) print("Centroid=(${xAvg},${yAvg})")}

Centroid3.kt

TheSegregationPrinciple

- Whichversionismorereusable?

Eachfunctionshouldhaveawell-definedobligation

funavg2(list:List<String>,index:Int):Float{valfList=list.map{it.split(",").get(index).toFloat()}valrVal=fList.fold(.0F){x,e->x+e}returnrVal/fList.size.toFloat()}

funavg1(list:List<Float>):Float{valrVal=list.fold(.0F){x,e->x+e}returnrVal/list.size.toFloat()}

UsingtheKotlinLibrary

- Whataretheadvantagesofusingthelibrary?Anddisadvantages?

- Canweimprovethisprogramevenfurther?

importjava.io.Filefunmain(args:Array<String>){valfile=File(args[0])vallines=file.readLines()valpoints=lines.drop(1)valxList=points.map{it.split(",").get(0).toFloat()}valxAvg=xList.average()valyList=points.map{it.split(",").get(1).toFloat()}valyAvg=yList.average()print("Centroid=(${xAvg},${yAvg})")}

Centroid4.kt

Unstructureddata

- Whatisthemeaningofthisline:it.split(",").get(1).toFloat()?

- Howdoweknowthatget(1)willgivebacksomething?

- Whatifthefilehasabadformat?

- Howmanythingscangowronginthiscase?

Unstructureddata





$cat~/Desktop/inst.csvX,Y3,30

Example of bad input IndexOutOfBoundsException

Unstructureddata





$cat~/Desktop/inst.csvX,Y3,30,frog

Another example of bad input NumberFormatException

Unstructureddata





- Howcanweimprovethisprogramtoeaseitsunderstanding?



OBJECTSANDCLASSES

ThePointClass

classPoint(valx:Float,valy:Float){ overridefuntoString():String{ return"(${x},${y})" }}

funline2Point(line:String):Point{ vallist=line.split(",") valx=list.get(0).toFloat() valy=list.get(1).toFloat() returnPoint(x,y)}

PointReader2.kt

- Whereistheconstructor?

- Howtoconvertafileintopoints?

Mappinglinesintopoints

funmain(args:Array<String>){valfile=File(args[0])vallines=file.readLines()vallDrop=lines.drop(1)valpoints=lDrop.map{line2Point(it)}points.forEach{println(it)}}

PointReader2.kt

$kotlincPointReader2.kt-include-runtime-dpointReader.jar$java-jarpointReader.jar~/Desktop/inst.csv(3.0,3.0)(0.0,4.0)(-1.0,-2.0)(1.0,3.0)(2.0,2.0)

BackintoCentroids

- CanyouusethenewclassPointtosolvetheproblemoffindingcentroids?

BackintoCentroids

- CanyouusethenewclassPointtosolvetheproblemoffindingcentroids?

funmain(args:Array<String>){valfile=File(args[0])vallines=file.readLines()vallDrop=lines.drop(1)valpoints=lDrop.map{line2Point(it)}valxAvg=points.map{it.x}.average()valyAvg=points.map{it.y}.average()print("Centroid=(${xAvg},${yAvg})\n")}

Example:RandomPairs.kt

Implementaprogramthatreadsatxtfilecontainingalistofstudents,andorganizesthestudentsintorandomteams.Thenumberofstudentsperteamisacommandlineargument.

$cats.txtARTURBRENOCAIOIVOJOÃOJOSEMATHEUSPEDROTHAISVINICIUS

Example of input

$java-jarrandomPairs.jars.txt3>[JOSE,ARTUR,CAIO]>[VINICIUS,JOÃO,MATHEUS]>[PEDRO,BRENO,THAIS]>[IVO]

$java-jarrandomPairs.jars.txt4>[PEDRO,CAIO,IVO,ARTUR]>[THAIS,MATHEUS,JOÃO,JOSE]>[BRENO,VINICIUS]

Example of outupt

Example:RandomPairs.kt

importjava.io.Filefunmain(args:Array<String>){valfile=File(args[0])valteamSize=args[1].toInt()vallines=file.readLines()valshuffled=lines.shuffled()valchunked=shuffled.chunked(teamSize)chunked.forEach{println(">$it")}}

RandomPairs.kt

- Whatwouldhappenifwedonotinformenoughcommandlinearguments?

$java-jarrandomPairs.jars.txtExceptioninthread"main"java.lang.ArrayIndexOutOfBoundsException:1atRandomPairsKt.main(RandomPairs.kt:5)

Missing argument

Checkinginputarguments

- Modifytheprogram,sothatitreportsamissingargument,andasksuserstousetheexpectedsyntax.

Checkingthenumberofargumentsinthecommandline

importjava.io.Filefunmain(args:Array<String>){if(args.size<2){System.err.println("Syntax:cmd<file.txt><teamSize>")}else{valfile=File(args[0])valteamSize=args[1].toInt()vallines=file.readLines()valshuffled=lines.shuffled()valchunked=shuffled.chunked(teamSize)chunked.forEach{println(">$it")}}}

RandomPairs.kt

$java-jarrandomPairs.jars.txtSyntax:cmd<file.txt><teamSize>

Introductionevcomp.dcc.ufmg.br/wp-content/uploads/Kotlin-Intro.pdf · 1. Supercell: The Finnish...

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