Welcome Kotlin!

A Kotlin introductory talk for the first mettup of the Kotlin User Group Milano (www.meetup.com/it-IT/KUG-Milan/)

Transcript

2. Welcome Kotlin!
3. Why Kotlin? • Big Java codebases at JetBrains • Java is old and has some major problems • Java slow development
4. Statically typed programming language for modern multi-platform applications
5. History of the language
6. July 2011 JetBrains publicly unveils a new statically typed programming language for the JVM with first-class IDE support
7. February 2012 • Apache 2.0 Open-Source license • github.com/JetBrains/Kotlin • Kompiler • IntelliJ IDEA plugin • Issue Tracker Kotlin goes Open Source
8. April 2015 • Library for Android development • DSL to build Android layouts • Collection of very useful utilities to make Android development easier • Open Source Anko for Android is revealed
10. February 2016 • Stable release • Production ready • Long-term backward compatibility Version 1.0 released
11. May 2016 • Gradle scripts written in Kotlin • Statically-typed DSL Kotlin meets Gradle
12. March 2017 • Stable JavaScript support • Experimental support for coroutines • Type aliases, bound callable references, destructuring in lambdas Version 1.1 released
13. Android first-class support for Kotlin ! May 2017
14. • Kotlin bundled in Android Studio 3.0 • Google commitment to the language • Improved support on Android Android first-class support for Kotlin ! May 2017
16. Concise Interoperable Safe Tools friendly Philosophy
17. Concise • Variable declaration • String templates /* Read only */ val a: Int = 1 // Explicit type
 val b = 2 // Type inferred /* Mutable */ var mutable = 2
 mutable = 4 // Reassignment val world = "World!"
 
 val helloWorld1 = "Hello $world" // -> Hello World!
 val helloWorld2 = "Hello ${world.replace("!", "!!!")}" // -> Hello World!!!
18. Concise data class Document(
 val name: String,
 val author: String,
 val creationDate: Date = Date()) val doc = Document(name = "Welcome Kotlin!", author = "Giacomo Bresciani") documents.filter { it.author == "Giacomo Bresciani" } 
 .sortedBy { it.name } 
 .forEach { print(it.name) } • Data classes • Named parameter & default values • Collections utils
19. Safe val string: String = null Compilation error! val stringNullable: String? = null stringNullable.length Compilation error! stringNullable?.length // -> Null val stringLengthNullable: String? = stringNullable?.length?.toString() // -> Null • Null Safety val stringLength: String = stringNullable?.length?.toString() ?: "No string” stringNullable!!.length // Safe calls // Elvis operator // !! Operator NullPointerException
20. Safe • “Immutability” fun printDocument(unknownDocument: Any) {
 if (unknownDocument is Document) 
 print(unknownDocument.name)
 } • Smart Cast val doc = Document(name = "Welcome Kotlin!", author = "Giacomo Bresciani") doc = Document(name = “New Document", author = “Peter Parker”) Compilation error!
21. Interoperable • Java from Kotlin • Kotlin from Java import java.util.Date val now = Date() now.time // equivalent to now.getTime() Document doc = new Document("Welcome Kotlin!", "Giacomo Bresciani", new Date()); String author = doc.getAuthor();
22. Tools friendly • Java to Kotlin converter • Kotlin bytecode decompiler • A lot of IntelliJ “Intention Actions” (alt + Enter) • Syntax highlight
23. Kotlin Features
24. First class functions { text: String, separator: Char -> text.split(separator) } • Lambdas val lambda: (String, Char) -> List<String> = 
 { text: String, separator: Char -> text.split(separator) } • High-order functions listOf(1, 2, 3).map({ int: Int -> int * 3 }) listOf(1, 2, 3).map { int: Int -> int * 3 } listOf(1, 2, 3).map { it * 3 } Kotlin Features
25. Extension functions fun String.isShorterThan(s: String): Boolean = this.length < s.length • Definition • Usage "Short".isShorterThan("Longer String") // True
 "Looooooooooooong String".isShorterThan("Shorter String") // False • Infix notation infix fun String.isShorterThan(s: String): Boolean = this.length < s.length "Short" isShorterThan "Longer String" // True
 "Looooooooooooong String" isShorterThan "Shorter String" // False Kotlin Features
26. Everything is an expression val ageTitle = if(age < 18) "underage" else “adult" • If • When (Java’s switch with superpowers) val ageTitle = when {
 age < 18 -> "underage"
 age in 18..64 -> "adult"
 else -> "senior"
 } • Try-Catch val int: Int? = try { "23d".toInt() } catch (nfe: NumberFormatException) { null } Kotlin Features
27. Sealed classes (AKA algebraic data types or sum types) sealed class ViewState {
 object Loading: ViewState()
 data class Error(val message: String): ViewState()
 data class Ready(val content: String): ViewState()
 } • Definition • When fun render(currentState: ViewState) = when (currentState) {
 ViewState.Loading -> print("Loading...")
 is ViewState.Error -> print(currentState.message)
 is ViewState.Ready -> print(currentState.content)
 } Kotlin Features
28. Kotlin Standard Library • A lot of utils ext. functions to query collections public inline fun <T> Iterable<T>.forEach(action: (T) -> Unit): Unit public inline fun <T> Iterable<T>.filter(predicate: (T) -> Boolean): List<T> public fun <T> List<T>.asReversed(): List<T> public inline fun <T> Iterable<T>.find(predicate: (T) -> Boolean): T? Kotlin Features public inline fun <T> T.apply(block: T.() -> Unit): T public inline fun <T, R> T.let(block: (T) -> R): R public inline fun <T : Closeable?, R> T.use(block: (T) -> R): R • Functions implementing idiomatic patterns
29. Testing
30. Options • You can still of course use JUnit • Mockito, Hamcrest… • You can write really expressive tests • Core library: kotlin.test Testing
31. Libraries • Spek - Specification Framework for the JVM class SumTest : Spek({
 describe("sum() function") {
 it("should return the sum of first number plus the second number") {
 val sum = sum(2, 4)
 assertEquals(6, sum)
 }
 }
 }) • KotlinTest - flexible and comprehensive testing tool “my string".length shouldBe 9 “hello" shouldNot haveSubstring(“olleh")
32. Getting started
33. Getting started • Bundled into recent version of IntelliJ IDEA and Android Studio 3.0 • Plugin available for Android Studio < 3.0 • Plugin available also for Eclipse • Build with Gradle, Maven, Ant
34. Kotlin Koans
35. Kotlin Koans
36. Kotlin REPL
37. First steps • Write some unit tests • Write some Utils functions • Introduce it gradually into you codebase • Experiment with pet project
38. Tips! • Use the IntelliJ built-in Java converter • Force you to write idiomatic Kotlin code • Explore Kotlin stdlib • Keep calm and write readable code!
39. Contribute!
40. Contribute! • KEEP - Kotlin Evolution and Enhancement Process github.com/Kotlin/KEEP • Proposal for the language (repo issues) • Issue Tracker - youtrack.jetbrains.com/issues/KT • Slack - slack.kotlinlang.org
41. Resources "
42. Books Resources • Kotlin in Action • Kotlin for Android Developers by Dmitry Jemerov and Svetlana Isakova by Antonio Leiva
43. Other resources Resources • Kotlin Weekly • Kotlin Official Blog • Awesome Kotlin - kotlin.link • Talking Kotlin (podcast) - talkingkotlin.com
44. Thank you! github.com/brescia123 @brescia123 Android Engineer @ Facile.it