Kotlin Introduction

Slides for my introduction to Kotlin talk - find the sample code over here https://github.com/techdev-solutions/kotlin-spring-demo

Transcript

1. #kotlin @alexhanschke Kotlin Introduc-on Java User Group Frankfurt – 26.07.2017
2. #kotlin @alexhanschke OHAI @alexhanschke •  working at techdev Solu6ons GmbH in Berlin •  doing Java since 2008, and •  Kotlin since 2016
3. #kotlin @alexhanschke Goals •  give a gentle introduc6on •  cover most relevant features (breath, not depth) •  whet your appe6te •  no prerequisites; Java knowledge helps
4. #kotlin @alexhanschke Agenda •  History •  Func6ons •  Expressions •  Classes & Types •  Extensions •  Null-safety •  Demo
5. #kotlin @alexhanschke Kotlin?
6. #kotlin @alexhanschke Kotlin!
7. #kotlin @alexhanschke Kotlin.. •  is a sta6cally-typed language •  compiles to Java bytecode, JavaScript, or machine code (Kotlin/Na6ve) •  is open source
8. #kotlin @alexhanschke Why Kotlin? •  JetBrains used Java in most of their tools •  need for a language that is concise, expressive, toolable, interoperable and pragma6c •  Java too slow to catch up •  Scala had the right features, but compiler was too slow
9. #kotlin @alexhanschke Philosophy Kotlin is a pragma-c, concise, safe language with a focus on interoperability.
10. #kotlin @alexhanschke History 2017 2016 2010 Project start Version 1.0 Version 1.1.3
11. #kotlin @alexhanschke Func-ons
12. #kotlin @alexhanschke Func-ons fun main(args: Array<String>): Unit { println("global") }
13. #kotlin @alexhanschke Func-ons fun main(args: Array<String>) { println("global") }
14. #kotlin @alexhanschke Func-ons fun main(args: Array<String>) { fun local() { println("local") } }
15. #kotlin @alexhanschke Func-ons fun main(args: Array<String>) { fun whee() { fun eee() { fun eeee() { } } } }
16. #kotlin @alexhanschke Func-ons fun `should never end`() { ..}
17. #kotlin @alexhanschke Func-ons class Person { fun greet() { println("hello!") } } fun main(args: Array<String>) { Person().greet() }
18. #kotlin @alexhanschke Func-ons fun block(): String { return "return type required" } fun expression() = "return type inferred"
19. #kotlin @alexhanschke Func-ons fun url(protocol: String, domain: String, port: Int): String { return "$protocol: //$domain:$port" } url("http", "example.com", 80) url(domain = "example.com", port = 80, protocol = "http")
20. #kotlin @alexhanschke Func-ons fun url(protocol: String = "http", domain: String, port: Int): String { return "$protocol: //$domain:$port" } url(domain = "example.com", port = 80)
21. #kotlin @alexhanschke Func-ons File: playground.kt fun url(protocol: String = "http", domain: String, port: Int): String { return "$protocol: //$domain:$port" } File: App.java public class App { public static void main(String ... args) { PlaygroundKt.url("http", "example.com", 80); } }
22. #kotlin @alexhanschke Func-ons File: playground.kt @file:JvmName("Playground") fun url(protocol: String = "http", domain: String, port: Int): String { return "$protocol: //$domain:$port" } File: App.java public class App { public static void main(String ... args) { Playground.url("http", "example.com", 80); } }
23. #kotlin @alexhanschke Func-ons File: playground.kt @file:JvmName("Playground") @JvmOverloads fun url(protocol: String = "http", domain: String, port: Int): String { return "$protocol: //$domain:$port" } File: App.java public class App { public static void main(String ... args) { Playground.url("example.com", 80); } }
24. #kotlin @alexhanschke Variables val name: String = "Kotlin"
25. #kotlin @alexhanschke Variables val name = "Kotlin"
26. #kotlin @alexhanschke Variables fun main(args: Array<String>) { val name: String name = "Kotlin" }
27. #kotlin @alexhanschke Variables fun main(args: Array<String>) { var name = "Java" name = "Kotlin" }
28. #kotlin @alexhanschke Variables val even: (Int) -> Boolean = { value: Int -> value % 2 == 0 }
29. #kotlin @alexhanschke Variables val even: (Int) -> Boolean = { it % 2 == 0 } fun test(predicate: (Int) -> Boolean, candidate: Int) { if (!predicate(candidate)) { throw IllegalArgumentException() } } fun main(args: Array<String>) { test(even, 2) }
30. #kotlin @alexhanschke Variables typealias IntPredicate = (Int) -> Boolean val even: IntPredicate = { it % 2 == 0 } fun test(predicate: IntPredicate, candidate: Int) { if (!predicate(candidate)) { throw IllegalArgumentException() } } fun main(args: Array<String>) { test(even, 2) }
31. #kotlin @alexhanschke Expressions
32. #kotlin @alexhanschke Expressions fun min(x: Int, y: Int) = if (x < y) x else y
33. #kotlin @alexhanschke Expressions fun parse(value: String) = try { Integer.parseInt(value) } catch (cause: Exception) { """¯\_(ツ)_/¯""" }
34. #kotlin @alexhanschke Expressions fun boom() { throw IOException("boom!") } Meanwhile in Java .. public static void main(String ... args) { try { Playground.boom(); } catch (IOException cause) { ..} } Does not compile IOException is never thrown in that block
35. #kotlin @alexhanschke Expressions @Throws(IOException ::class) fun boom() { throw IOException("boom!") } Meanwhile in Java .. public static void main(String ... args) { try { Playground.boom(); } catch (IOException cause) { ..} }
36. #kotlin @alexhanschke Expressions fun status(code: Int) = when (code) { in 100 ..199 -> "info" in 200 ..299 -> "success" in 300 ..399 -> "redirect" in 400 ..499 -> "client error" in 500 ..599 -> "server error" else -> "unknown" }
37. #kotlin @alexhanschke Expressions fun status(code: Int) = when { code in 100 ..199 -> "info" code in 200 ..299 -> "success" code in 300 ..399 -> "redirect" code in 400 ..499 -> "client error" code in 500 ..599 -> "server error" else -> "unknown" }
38. #kotlin @alexhanschke Classes
39. #kotlin @alexhanschke Classes public class Commit {( ( private String hash;( private String author;( ( public String getAuthor() {( return author;( }( ( public void setAuthor(String author) {( this.author = author;( }( ( public String getHash() {( return hash;( }( ( public void setHash(String hash) {( this.hash = hash;( }( } class Commit(val hash: String, var author: String) val commit = Commit("abc123", "alexhanschke") commit.author = "john.doe" Defaults All classes are public and final by default.
40. #kotlin @alexhanschke Classes @lombok.Data public class Commit {( ( private String hash;( private String author; ( } / ** •  toString() •  equals() •  hashCode() •  Getter & Setter */ data class Commit(val hash: String, var author: String) val one = Commit("abc123", "alexhanschke") val two = one.copy(hash = "xyz123")
41. #kotlin @alexhanschke Classes abstract class Shape class Rectangle : Shape() { fun area(): Double { ..} } class Square : Rectangle() { override fun area(): Double { ..} }
42. #kotlin @alexhanschke Classes abstract class Shape open class Rectangle : Shape() { open fun area(): Double { ..} } class Square : Rectangle() { override fun area(): Double { ..} }
43. #kotlin @alexhanschke Extensions
44. #kotlin @alexhanschke Extension Func-ons fun Int.squared() = this * this 3.squared() // 9 fun List<String>.random(): String { if (this.isEmpty()) { throw IllegalStateException("List must not be empty.") } return this[Random().nextInt(this.size)] } listOf("a", "b", "c").random()
45. #kotlin @alexhanschke Extension Func-ons fun Int.squared() = this * this 3.squared() // 9 fun List<String>.random(): String { if (this.isEmpty()) { throw IllegalStateException("List must not be empty.") } return this[Random().nextInt(this.size)] } Playground.random(List<String> receiver)
46. #kotlin @alexhanschke Extension Func-ons •  extension func6ons allow adding behavior to exis6ng types •  sta6cally resolved •  don't break encapsula6on •  member func6ons take precedence
47. #kotlin @alexhanschke Extension Proper-es class Person(val name: String) val Person.email: String get() = "$name@example.com" Person("alex").email // alex@example.com "text goes here" ::class // kotlin.String "text goes here" ::class.java // java.lang.String
48. #kotlin @alexhanschke Null-safety
49. #kotlin @alexhanschke Type System String Any String? Any?
50. #kotlin @alexhanschke Null-safety class Commit(val hash: String, var author: String?) fun main(args: Array<String>) { val commit: Commit? = null println(commit.author) // Compiler: err, no. }
51. #kotlin @alexhanschke Null-safety class Commit(val hash: String, var author: String?) val commit: Commit? = null if (commit != null) { if (commit.author != null) { commit.author.reversed() } } Smart Casts The compiler automagically casts a given type when applicable.
52. #kotlin @alexhanschke Null-safety class Commit(val hash: String, var author: String?) val commit: Commit? = null commit?.author?.reversed()
53. #kotlin @alexhanschke Null-safety class Commit(val hash: String, var author: String?) val commit: Commit? = null val name = commit?.author ?: "elvis"
54. #kotlin @alexhanschke Null-safety class Commit(val hash: String, var author: String?) val commit: Commit? = null val name = commit?.author ?: throw IllegalArgumentException("author required")
55. #kotlin @alexhanschke Null-safety class Commit(val hash: String, var author: String?) val commit: Commit? = null commit !!.author !!.reversed()
56. #kotlin @alexhanschke Sample
57. #kotlin @alexhanschke Resources -  www.kotlinweekly.net -  h[ps://kotlin.link/ -  h[ps://github.com/techdev-solu6ons/janitor -  h[ps://jaxenter.de/kotlin-tutorial-48156 -  h[ps://jaxenter.de/kotlin-ein-tutorial-fuer-einsteiger-teil-2-48587 -  h[ps://jaxenter.de/kotlin-ein-tutorial-fuer-einsteiger-teil-3-48967 -  h[ps://jaxenter.de/kotlin-ein-tutorial-fuer-einsteiger-teil-4-49160
58. #kotlin @alexhanschke Thank you!