Getting Started with Kotlin. Commerzbank Java Developer Day

Transcription

1 Getting Started with Kotlin Commerzbank Java Developer Day

2 Hello! Alexander Hanschke

3 Hello! Alexander Hanschke CTO at techdev Solutions GmbH in Berlin

4 Hello! Alexander Hanschke CTO at techdev Solutions GmbH in Berlin Java since 2008, and

5 Hello! Alexander Hanschke CTO at techdev Solutions GmbH in Berlin Java since 2008, and Kotlin since 2016

6 Goals

7 Goals give a gentle introduction

8 Goals give a gentle introduction cover most relevant features (breath, not depth)

9 Goals give a gentle introduction cover most relevant features (breath, not depth) whet your appetite

10 Goals give a gentle introduction cover most relevant features (breath, not depth) whet your appetite prerequisites: Java, Spring (Boot)

11 Agenda

12 Agenda History

13 Agenda History Part I Functions, Classes, Exceptions & Null-Safety

14 Agenda History Part I Functions, Classes, Exceptions & Null-Safety Part II Demo

15 Agenda History Part I Functions, Classes, Exceptions & Null Safety Part II Demo Q & A

16 Kotlin?

17 Kotlin!

18 Kotlin..

19 Kotlin.. is a statically-typed language

20 Kotlin.. is a statically-typed language compiles to Java bytecode, JavaScript, or machine code (Kotlin/Native)

21 Kotlin.. is a statically-typed language compiles to Java bytecode, JavaScript, or machine code (Kotlin/Native)

22 Kotlin.. is a statically-typed language compiles to Java bytecode, JavaScript, or machine code (Kotlin/Native) is open-source

23 Why Kotlin?

24 Why Kotlin? JetBrains used Java in most of their tools

25 Why Kotlin? JetBrains used Java in most of their tools need for a language that is concise, expressive, toolable, interoperable and pragmatic

26 Why Kotlin? JetBrains used Java in most of their tools need for a language that is concise, expressive, toolable, interoperable and pragmatic Java too slow to catch up

27 Why Kotlin? JetBrains used Java in most of their tools need for a language that is concise, expressive, toolable, interoperable and pragmatic Java too slow to catch up Scala had the right features, but compiler was too slow

28 Philosophy Kotlin is a pragmatic, concise, safe language with a focus on interoperability.

29 History Project start Version 1.0 Version 1.2.0

30 Part I

31 Functions fun main(args: Array<String>): Unit { println("hello World!") }

32 Functions fun main(args: Array<String>) { println("hello World!") }

33 Functions fun main(args: Array<String>) = println("hello World!")

34 Functions fun url(protocol: String, domain: String, port: Int) { println("$protocol:!//$domain:$port") }

35 Functions fun url(protocol: String, domain: String, port: Int) { println("$protocol:!//$domain:$port") } url("http", "techdev.io", 80)!//

36 Functions fun url(protocol: String, domain: String, port: Int) { println("$protocol:!//$domain:$port") } url("http", "techdev.io", 80) url(domain = "techdev.io", port = 80, protocol = "http")

37 Functions fun url(protocol: String = "http", domain: String, port: Int = 80) { println("$protocol:!//$domain:$port") } url(domain = "techdev.io")

38 Functions File: Kotlin.kt fun url(protocol: String = "http", domain: String, port: Int = 80) { println("$protocol:!//$domain:$port") }

39 Functions File: Kotlin.kt fun url(protocol: String = "http", domain: String, port: Int = 80) { println("$protocol:!//$domain:$port") } File: Java.java public class Java { public static void main(string!!... args) { KotlinKt.url("http", "techdev.io", 80); } }

40 Functions File: fun url(protocol: String = "http", domain: String, port: Int = 80) { println("$protocol:!//$domain:$port") } File: Java.java public class Java { public static void main(string!!... args) { AnotherName.url("http", "techdev.io", 80); } }

41 Functions fun url(protocol: String = "http", domain: String, port: Int = 80) { println("$protocol:!//$domain:$port") } File: Java.java public class Java { public static void main(string!!... args) { AnotherName.url("techdev.io"); } }

42 Extension Functions

43 Extension Functions fun Int.squared() = this * this

44 Extension Functions fun Int.squared() = this * this

45 Extension Functions fun Int.squared() = this * this 3.squared()!// 9

46 Extension Functions fun Int.squared() = this * this 3.squared()!// 9 fun List<String>.random() = this[random().nextint(this.size)]

47 Extension Functions fun Int.squared() = this * this 3.squared()!// 9 fun List<String>.random() = this[random().nextint(this.size)] listof("a", "b", "c").random()

48 Extension Functions fun Int.squared() = this * this 3.squared()!// 9 fun List<String>.random() = this[random().nextint(this.size)] listof("a", "b", c").random() KotlinKt.random(List<String> receiver);

49 Properties var age: Int = 42

50 Properties var age = 42

51 Properties var age = 42 val text = "final"

52 Classes

53 Classes (Java) public class Superhero { private final String name; private int strength; }

54 Classes (Java) public class Superhero { private final String name; private int strength; public Superhero(String name, int strength) { this.name = name; this.strength = strength; } }

55 Classes (Java) public class Superhero { private final String name; private int strength; public Superhero(String name) { this(name, 100); } public Superhero(String name, int strength) { this.name = name; this.strength = strength; } }

56 Classes (Java) public class Superhero { } private final String name; private int strength; public Superhero(String name) { this(name, 100); } public Superhero(String name, int strength) { this.name = name; this.strength = strength; } public String getname() {!..} public int getstrength() {!..} public void setstrength(int strength) {!..}

57 Classes (Kotlin) class Superhero(val name: String, var strength: Int = 100)

58 Classes (Kotlin) class Superhero(val name: String, var strength: Int = 100) val thor = Superhero("Thor") var enemy = Superhero("Hulk", 90)

59 Classes (Kotlin) class Superhero(val name: String, var strength: Int = 100) val thor = Superhero("Thor") var enemy = Superhero("Hulk", 90) println("${thor.name} vs. ${enemy.name}")!// Thor vs. Hulk

60 Classes (Kotlin) class Superhero(val name: String, var strength: Int = 100) val thor = Superhero("Thor") var enemy = Superhero("Hulk", 90) println("${thor.name} vs. ${enemy.name}")!// Thor vs. Hulk new Superhero("Spider-Man", 70).getName();

61 public class Superhero { } private final String name; private int strength;

62 Data Classes data class Superhero(val name: String, var strength: Int = 100)

63 Data Classes data class Superhero(val name: String, var strength: Int = 100)

64 Exceptions

65 Exceptions fun parse(value: String) = try { Integer.parseInt(value) } catch (cause: NumberFormatException) { """ \_( ツ )_/ """ }

66 Exceptions fun boom() { throw IOException("boom o( ><)o") }

67 Exceptions fun boom() { throw IOException("boom o( ><)o") } public static void main(string!!... args) { try { KotlinKt.boom(); } catch (IOException cause) {!..} }

68 fun boom() { throw IOException("boom o( ><)o") } public static void main(string!!... args) { try { KotlinKt.boom(); } catch (IOException cause) {!..} }

69 Null Safety

70 Null Safety Superhero

71 Null Safety Any Superhero

72 Null Safety Any Any? Superhero

73 Null Safety Any Any? Superhero Superhero?

74 Null Safety class Item(val name: String) class Superhero(val name: String, var strength: Int = 100, val item: Item? = null) val thor = Superhero("Thor", item = Item("Hammer"))

75 Null Safety class Item(val name: String) class Superhero(val name: String, var strength: Int = 100, val item: Item? = null) val thor = Superhero("Thor", item = Item("Hammer"))

76 Null Safety class Item(val name: String) class Superhero(val name: String, var strength: Int = 100, val item: Item? = null) val thor = Superhero("Thor", item = Item("Hammer")) println(thor.item.name)!// nope.

77 Null Safety class Item(val name: String) class Superhero(val name: String, var strength: Int = 100, val item: Item? = null) val thor = Superhero("Thor", item = Item("Hammer")) if (thor.item!!= null) { println((thor.item as Item).name)!// Hammer }

78 Null Safety class Item(val name: String) class Superhero(val name: String, var strength: Int = 100, val item: Item? = null) val thor = Superhero("Thor", item = Item("Hammer")) if (thor.item!!= null) { println(thor.item.name)!// Hammer }

79 Null Safety class Item(val name: String) class Superhero(val name: String, var strength: Int = 100, val item: Item? = null) val thor = Superhero("Thor", item = Item("Hammer")) println(thor.item!?.name)

80 Null Safety class Item(val name: String) class Superhero(val name: String, var strength: Int = 100, val item: Item? = null) val thor = Superhero("Thor", item = Item("Hammer")) println(thor.item!?.name!?: "No Item")

81 Null Safety class Item(val name: String) class Superhero(val name: String, var strength: Int = 100, val item: Item? = null) val thor = Superhero("Thor", item = Item("Hammer")) println(thor.item!!!.name)

82 Philosophy Kotlin is a pragmatic, concise, safe language with a focus on interoperability.

83 How to get started?

84 How to get started? write tests in Kotlin

85 How to get started? write tests in Kotlin replace utility classes with extension functions

86 How to get started? write tests in Kotlin replace utility classes with extension functions add new components in Kotlin

87 How to get started? write tests in Kotlin replace utility classes with extension functions add new components in Kotlin replace existing components one-by-one as you see fit

88 Things to consider

89 Things to consider there is a company behind it

90 Things to consider there is a company behind it SCM history may be lost changing from.java to.kt

91 Things to consider there is a company behind it SCM history may be lost changing from.java to.kt classes are closed by default

92 Things to consider there is a company behind it SCM history may be lost changing from.java to.kt classes are closed by default no implicit widening conversion for numbers

93

94 Part II

95 Thank you!

96 Q & A