Develop a reactive A app with K #DevFest Toulouse 2016

@arnogiu Work @ ekito App & Gear Maker Fullstack Mobile Dev Arnaud GIULIANI What’s ekito ?

3 « production ready » 15.02.2016

4 Yet another JVM Language ?

5 The new « Swift » for Android ? https://goo.gl/W5g6Do - mid 2014

Limits of java - Verbose - Type inference - No properties / Lazy / Delegate - Checked exception - NullPointerException - Extensibility - End of lines with ; https://goo.gl/HIrmC9 @sdeleuze

But Java is great … - Fast - Optimized bytecode - Static typing - Simple to learn - Amazing ecosystem

What’s Kotlin ? - Built by Jetbrains & fully Open Source - Run on Java VM 6 & + - Static typing (type inference) - Modern language - Easy to Read & Learn - Concise & Fast to write - Fully interoperable with Java - 1st grade tooling

What’s inside Kotlin ? - String templates - Properties - Lambdas - Data class - Smart cast - Null safety - Lazy property - Default values for function parameters - Extension Functions - No more ; - Single-expression functions - When expression - let, apply, use, with - Collections - Android Extensions Plugin

How K can help you ? - Reduce common errors & boiler code - Make safer API - Help keep focus on your business - Interoperable java alternative Can be used almost everywhere Java is used today !

Compare with Same conciseness and expressive code, but Kotlin static typing and null-safety make a big difference. "Some people say Kotlin has 80% the power of Scala, with 20% of the features" * 
 "Kotlin is a software engineering language in contrast to Scala which is a computing science language." * Swift and Kotlin are VERY similar. Swift is LLVM based and has C interop while Kotlin is JVM based and has Java interop. * Quotes from Kotlin: The Ying and Yang of Programming Languages

Use Cases Source : poll on Kotlin Slack https://goo.gl/HIrmC9 @sdeleuze

13 Want some nougat ?

14 Slowing Deployment https://goo.gl/2sOGBd

15 is Kotlin Android friendly ? https://github.com/SidneyXu/AndroidDemoIn4Languages Method counts by Language

16 Well … let’s get some Kotlin !

Develop & have fun with K * Being productive again !

18 Getting started with gradle buildscript { ext.kotlin_version = '' dependencies { classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version" } } apply plugin: "kotlin" dependencies { compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version" } Actual Version : 1.0.4

19 IntelliJ - Plugin

20 IntelliJ - Menus

21 Typing & Inference val a: Int = 1
 val b = 1 // `Int` type is inferred
 val c: Int // Type required when no initializer is provided
 c = 1 // definite assignment var x = 5 // `Int` type is inferred
 x += 1 Infered values Mutable values val : constant value var : variable value

val length = stringB.length // Compilation error - stringB can be null !
 // use ? the safe call operator
 val length = stringB?.length //Value or null - length is type Int? val length = stringB!!.length // Value or explicit throw NPE - length is type Int 22 Safety with Optionals var stringA: String = "foo"
 stringA = null //Compilation error - stringA is a String (non optional)
 
 var stringB: String? = "bar" // stringB is an Optional String
 stringB = null //ok Safe call with ?. or Explicit call !!. Optional value

23 Safety again ! val name = "Arnaud"
 var s : String // Compilation error
 lateinit var s : String // late initialized variable // if s is not set throw an NPE
 fun testHello() {
 s = "Hello $name" //…
 } Lazy, Delegates … Late initialization // set length default value manually
 val length = if (stringB != null) stringB.length else -1
 //or with the Elvis operator
 val length = stringB?.length ?: -1 Default Value & Elvis Operator

24 Example - Activity

25 Class class User (
 var userName: String,
 var firstName: String,
 var lastName: String,
 var location: Point? = null
 ) POJO + - Getter - Setter - Constructors

26 Data Class data class User (
 var userName: String,
 var firstName: String,
 var lastName: String,
 var location: Point? = null
 ) POJO + - Getter - Setter - Constructors - toString - hashcode - equals - copy

27 No Static, think Object // my resource singleton
 object Resource {
 val name = "Name"
 } println(" my resource is : ${Resource.name}") class StringCalculator{
 companion object{
 val operators = arrayOf("+","-","x","/")
 }
 } println(" my operators are : ${StringCalculator.operators}") Object (good old singleton ;-) ) Companion Object

28 Example data class User(val name: String = "", val age: Int = 0) val jack = User(name = "Jack", age = 1)
 val anotherJack = jack.copy(age = 2) json class data class handling

29 When when (s) {
 1 -> print("x == 1")
 2 -> print("x == 2")
 else -> { // Note the block
 print("x is neither 1 nor 2")
 }
 } Flow Control (replace your old if blocks) when (x) {
 in 1..10 -> print("x is in the range")
 in validNumbers -> print("x is valid")
 !in 10..20 -> print("x is outside the range")
 else -> print("none of the above")
 } Pattern Matching in -> is -> expression -> when (s) {
 is String -> print("s is a string")
 else -> print("s is not a string")
 }

30 Example

31 Functions fun reformat(str: String,
 normalizeCase: Boolean = true,
 upperCaseFirstLetter: Boolean = true,
 wordSeparator: Char = ' '): String {
 
 //...
 } Named Parameters & default values reformat(str, true, true, '_') // old way to call
 reformat(str, wordSeparator = '_') // using default values & named params fun String.hello(): String{
 return "Hello " + this
 } val hi = "Arnaud !".hello()
 println("$hi") // Hello Arnaud ! Extension

32 Lambdas val fab = findViewById(R.id.fab) as FloatingActionButton
 fab.setOnClickListener { view -> popLocationDialog(view) } A lambda expression or an anonymous function is a “function literal”, i.e. a function that is not declared, but passed immediately as an expression - A lambda expression is always surrounded by curly braces, - Its parameters (if any) are declared before -> (parameter types may be omitted), - The body goes after -> (when present). numberString.split("\n").flatMap { it.split(separator) }
 .map(Integer::parseInt)
 .map(::checkPositiveNumber)
 .filter { it <= 1000 }
 .sum()

33 Destructuring Data fun extractDelimiter(input: String): Pair {
 return … } val (separator, numberString) = extractDelimiter(input) data class User(var name : String,var age : Int) val toto = User("toto",42) // …
 val (name,age) = toto Returning two values with Pair Destructured values

34 Collections // immutable list
 val list = listOf("a", "b", "c","aa")
 list.filter { it.startsWith("a") } // immutable map
 val map = mapOf("a" to 1, "b" to 2, "c" to 3)
 for ((k, v) in map) {
 println("$k -> $v")
 } 
 // mutable map
 val map2 = HashMap() 
 // direct map access
 map2["a"] = "my value"
 println(map2["a"]) // range
 for (i in 1..100) { //... }

35 Java InterOp object UserSingleton{
 fun stringify(user : User) : String{
 val (name,age) = user
 return "[name=$name][age=$age]"
 }
 }
 
 fun WhatIsyourAge(user : User){
 println("Your age is ${user.age}")
 }
 
 data class User (val name: String, val age : Int){
 companion object{
 fun sayHello(user : User){
 println("Hello ${user.name}")
 }
 }
 } User u = new User("toto",42);
 User.Companion.sayHello(u);
 UserUtilsKt.WhatIsyourAge(u);
 System.out.println("stringify : "+UserSingleton.INSTANCE.stringify(u)); Kotlin code Calling Kotlin from Java

Sweet stuffs for

Gradle tips for Kotlin # Gradle
 org.gradle.jvmargs=-Xmx2048m -XX:MaxPermSize=512m -XX: +HeapDumpOnOutOfMemoryError -Dfile.encoding=UTF-8
 org.gradle.parallel=true
 
 # Kotlin
 kotlin.incremental=true
 
 # Android Studio 2.2+
 android.enableBuildCache=true In your gradle.properties https://medium.com/keepsafe-engineering/kotlin-vs-java-compilation-speed-e6c174b39b5d#.k44v7axsk

38 Kotlin’s Android Extensions android { ... sourceSets { main.java.srcDirs += 'src/main/kotlin' } } apply plugin: 'com.android.application' apply plugin: ‘kotlin-android’ apply plugin: ‘kotlin-android-extensions’ // if use extensions In your build.gradle

Android Extensions No more findViewById !!! Kotlin Java

Anko - Android Dev on steroïds Async task in few lines doAsync { // Long background task uiThread { result.text = "Done" } } Layout DSL verticalLayout { val name = editText() button("Say Hello") { onClick { toast("Hello, ${name.text}!") } } } https://github.com/Kotlin/anko

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Reactive Programming

Reactive Programming Lamba expressions Functional Programming Reactive Streams http://reactivex.io/documentation/operators.html http://www.reactive-streams.org/ https://spring.io/blog/2016/06/07/notes-on-reactive- programming-part-i-the-reactive-landscape

44 Example - Rx/Retrofit Kotlin Java

45 Example - Rx/Realm

46 Learning Kotlin

47 Try Kotlin online http://try.kotlinlang.org/#/Examples/ Kotlin Reference https://kotlinlang.org/docs/reference/ Kotlin Cheat Sheet (by ekito) http://www.slideshare.net/arnaudgiuliani/kotlin- cheat-sheet-by-ekito Kotlin Community https://kotlinlang.org/community.html

48 Kotlin 1.1

49 Demo ! https://github.com/Ekito/reactiveweather-android

50 The Reactive Weather App Demo My Weather App Google Geocode WS Wunderground WS Weather SDK Last Weather

Thank you :)