Introduction to Kotlin and it's advantages against Java (Slides from the Nighthacking in Munich at Eppleton IT Consulting.)

1. Kotlin für Android/Java-
Entwickler
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2. Agenda
I. Einführung
II. Setup
III. Kotlin
1. Variablen und Konstanten
2. Funktionen
3. Klassen
4. Optionals
5. Kontroll-Fluss
6. Extensions
7. Lambdas
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3. Wieso Kotlin?
Concise SafeInter-
operable
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4. Anwendungsgebiete
JVM Android Browser Native
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5. Firmen, die Kotlin nutzen
Evernote
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6. Java-to-Kotlin Converter
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7. Setup
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8. Setup
https://github.com/quickbirdstudios/KotlinBasics
1 2
3
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9. Just say NO
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10. Setup
appsrctestjavacomquickbirdstudioskotlinbasicsexercises
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11. Hacking
Führe alle Tests aus und stell sicher, dass alle Tests fehlschlagen
Run Tests in
‘exercises’
Rechtsklick…
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13. Bruno
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14. Variablen und Konstanten
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15. String myVariable = "Change me";
final String myConstant = "Can't change me";
var myVariable: String = "Change me“
val myConstant: String = "Can't change me"
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16. String myVariable = "Change me";
final String myConstant = "Can't change me";
var myVariable: String = "Change me“
val myConstant: String = "Can't change me"
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17. final String myConstant = "Can't change me";
String myVariable = "Change me";
val myConstant = "Can't change me"
var myVariable = "Change me"
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18. Funktionen
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19. Funktionen
fun bark(times: Int): String {
return "Wuff".repeat(times)
}
Function Keywort Return Typ
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20. Funktionen
fun bark(times: Int = 1): String {
return "Wuff".repeat(times)
}
Standard-Wert
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21. Funktionen
fun bark(times: Int = 1) = "Wuff".repeat(times)
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22. Aufrufen von Funktionen
dog.bark()
dog.bark(3)
dog.bark(times = 3)
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23. Klassen
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24. public class JavaHuman {
private String name;
private int age;
public JavaHuman(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public void sayHello(String otherPersonName){
System.out.println("Hi, nice to see you "+otherPersonName);
}
public void sayHello(){
sayHello("");
}
}
class KotlinHuman(var name: String, var age: Int) {
fun sayHello(otherPersonName: String = "") {
println("Hi, nice to see you $otherPersonName")
}
}
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25. Kotlin Klasse
class KotlinHuman(var name: String, var age: Int) {
fun sayHello(otherPersonName: String = "") {
println("Hi, nice to see you $otherPersonName")
}
}
Primary Constructor
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26. Kotlin Klasse
class KotlinHuman(var name: String, var age: Int) {
fun sayHello(otherPersonName: String = "") {
println("Hi, nice to see you $otherPersonName")
}
}
String template
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27. Getters and setters
class KotlinHuman(var name: String, var age: Int) {
var cityAddress = "Munich"
fun sayHello(otherPersonName: String = "") {
println("Hi, nice to see you $otherPersonName")
}
}
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28. Zugriff auf Properties
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val human = KotlinHuman()
human.cityAddress = "Hamburg“
val address = human.cityAddress

29. Getters and setters
class KotlinHuman(var name: String, var age: Int) {
var cityAddress = "Munich"
fun sayHello(otherPersonName: String = "") {
println("Hi, nice to see you $otherPersonName")
}
}
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30. Getters and setters
class KotlinHuman(var name: String, var age: Int) {
var cityAddress = “Munich"
get() = "City $field"
set(city) {
if (city.length < 3)
throw IllegalArgumentException("City less than 3 chars")
field = city
}
fun sayHello(otherPersonName: String = "") {
println("Hi, nice to see you $otherPersonName")
}
}
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31. Instantierung von Klassen
val myKotlinHuman = KotlinHuman("Bruno",5)
Kein “new” Keywort
mehr
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32. Hacking
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33. Syntax-Beispiel
class KotlinHuman(var name: String, var age: Int) {
fun sayHello(otherPersonName: String = "") {
println("Hi, nice to see you $otherPersonName")
}
}
return “Hallo".repeat(5)
Öffne 1_SimpleDogClass.kt
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34. Lösung
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private class Dog(var name: String, val type: String) {
fun bark(times: Int) = println("Wuff".repeat(times))
}
@Test
fun testMyNewDogClass() {
val dog = Dog("Bruno","Labrador")
dog.bark(3)
}

35. Optionals
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36. Nullpointer exceptions
public void sayHello(Dog otherDog){
System.out.println(“Wuff, "+ otherDog.getName());
}
sayHello(null);
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37. Kotlin Null-Sicherheit
fun sayHello(otherDog: Dog) {
println("Hi, " + dog.name);
}
sayHello(null);
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38. Compiler Error.
var dog: Dog = null
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39. Optionals als seperater Typ
var dog: Dog? = null
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40. Aufrufen von Kotlin Optionals
val dog: Dog? = findDog()
dog.bark()
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41. Aufrufen von Kotlin Optionals
val dog: Dog? = findDog()
if(dog != null){
dog.bark(3)
}
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42. Safe Call Operator
val dog: Dog? = findDog()
dog?.bark()
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43. For all NPE lovers
val dog: Dog? = findDog()
dog!!.bark()
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44. Elvis Operator
val myDog = findDog() ?: buyNewDog()
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45. Automatic casting
if(dog != null){
dog.bark(3)
}
val anyObject: Any = getAnimal()
if(anyObject is Dog){
anyObject.bark()
}
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46. Hacking
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47. Syntax-Beispiel
Öffne 2_Optionals.kt
human?.sayHello()
val myDog = findDog() ?: buyNewDog()
// Safe casts
val name = (any as? Cat)?.name
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48. Lösung
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private fun letDogBark(dog: Dog?) {
// TODO TASK 1
dog?.bark()
}
private fun getDogName(dog: Dog?): String {
// TODO TASK 2
return dog?.name ?: "No dog found"
}
private fun getNameOf(any: Any): String {
// TODO TASK 3
return (any as? Dog)?.name ?: "type unknown"
}

49. Kontrollfluss
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50. For Schleife
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val dogs = getDogs()
for (dog in dogs){
dog.bark()
}

51. For Schleife
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val dogs = getDogs()
for (index in 0..10){
dogs[index].bark()
}
Range Operator

52. When: Java Switch mit Superkräften
fun getDogPluralString(dogCount: Int): String {
when(dogCount){
0 -> return "Keine Hunde"
1 -> return "Ein Hund"
else -> return "$dogCount Hunde"
}
}
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53. When: Java Switch mit Superkräften
fun getDogPluralString(dogCount: Int): String {
when(dogCount){
0 -> return "Keine Hunde"
1 -> return "Ein Hund"
else -> return "$dogCount Hunde"
}
}
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54. When: Java Switch mit Superkräften
fun getDogPluralString(dogCount: Int): String {
return when(dogCount){
0 -> "Keine Hunde"
1 -> "Ein Hund"
else -> "$dogCount Hunde"
}
}
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55. When: Java Switch mit Superkräften
fun getDogPluralString(dogCount: Int) = when (dogCount) {
0 -> "Keine Hunde"
1 -> "Ein Hund"
else -> "$dogCount Hunde"
}
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56. When ohne Argument
fun evaluatePassword(password: String): String {
return when {
password.isEmpty() -> "Bitte gib ein Passwort ein"
password.length < 5 -> "Passwort ist nicht lang genug"
!password.containsNumber() -> "Passwort muss eine Ziffer enthalten"
else -> "Das Passwort ist valide"
}
}
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57. Hacking
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58. Syntax-Beispiel
Öffne 3_ControlFlow.kt
when(dogCount){
0 -> return "Keine Hunde"
1 -> return "Ein Hund"
else -> return "$dogCount Hunde"
}
return when (dogCount) {
in 0..4 -> "..."
4, 5 -> "..."
else -> "..."
}
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59. Lösung
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// TODO TASK 1
fun findDogOwnerName(dog: Dog): String? {
return when(dog.name){
"Bruno" -> "Hans"
"Ignatz" -> "Peter"
else -> null
}
}
// TODO TASK 2
fun ageToString(dog: Dog): String {
return when(dog.age){
0,1 -> "Baby Dog"
in 2..8 -> "Normal Dog"
else -> "Old Dog"
}
}

60. Extensions
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61. println("Ich heiße Bruno".barkify())
// “WUFF WUFF WUFF”
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62. Extension Funktion: Zahl gerade oder
ungerade
fun Int.isEven(): Boolean {
return this % 2 == 0
}
println(1.isEven()) // false
println(2.isEven()) // true
println(3.isEven()) // false
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63. Hacking
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64. Syntax-Beispiel
Öffne 4_Extensions.kt
fun Int.isEven(): Boolean {
return this % 2 == 0
}
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65. Lösung
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// TODO TAKS 1
fun String.scream(): String {
return this.toUpperCase()+"!!!"
}
// TODO TASK 2
private fun applyAllCapsExtension(text: String): String {
return text.scream()
}
@Test
fun testAllCapsDogLanguage() {
// TODO TASK 3
val allCapsDogLanguage = "Ich habe ganz viel Hunger".barkify().scream()
assertEquals("WUFF WUFF WUFF WUFF WUFF!!!", allCapsDogLanguage)
}

66. Lambdas & Higher Order Functions
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67. Lambda Funktionsreferenz
val dog = Dog("Bruno")
val bark = dog::bark
bark(times = 3)
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68. Lambda Definition
val dog = Dog("Bruno")
val greetDog: (Dog) -> String = { dog -> "Hey! ${dog.name}" }
println(greetDog(dog))
Parameter type Return type
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69. Lambda Definition
val dog = Dog("Bruno")
val greetDog: (Dog) -> String = { dog -> "Hey! ${dog.name}" }
println(greetDog(dog))
Parameter name Lambda Body
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70. Higher Order Functions: Filter
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71. Filtern von Hunden
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72. Filter Funktion
var dogs: List<Dog> = animals.filter(
…
)
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73. Filter Prädikat/Bedingung
{ animal -> animal is Dog }
??
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74. Filter Funktion
var dogs = animals.filter({ animal ->
animal is Dog
})
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75. Filter Funktion
var dogs = animals.filter(){ animal ->
animal is Dog
}
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76. Filter Funktion
var dogs = animals.filter { animal ->
animal is Dog
}
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77. Filter Funktion
var dogs = animals.filter { it is Dog }
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78. Higher Order Functions: Map
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79. Mapping von Hunden
age = 8 age = 2 age = 3age = 6 age = 11
age = 8 age = 2 age = 3age = 6 age = 11
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80. Mapping von Hunden
val dogs = listOf(Dog("Bello",age = 8),Dog("Rex",age = 2),
Dog("Lessi",age = 6),Dog("Bruno",age = 3),Dog("Bello",age = 11))
val dogAges = dogs.map { … }
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81. Map Prädikat/Bedingung
{ dog -> dog.age }
age = 8 age = 8
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82. Mapping von Hunden
val dogs = listOf(Dog("Bello",age = 8),Dog("Rex",age = 2),
Dog("Lessi",age = 6),Dog("Bruno",age = 3),Dog("Bello",age = 11))
val dogAges = dogs.map { dog -> dog.age }
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83. Mapping von Hunden
val dogs = listOf(Dog("Bello",age = 8),Dog("Rex",age = 2),
Dog("Lessi",age = 6),Dog("Bruno",age = 3),Dog("Bello",age = 11))
val dogAges = dogs.map { it.age }
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84. Mapping von Hunden
val dogs = listOf(Dog("Bello",age = 8),Dog("Rex",age = 2),
Dog("Lessi",age = 6),Dog("Bruno",age = 3),Dog("Bello",age = 11))
val dogAges = dogs.map { it.age }
val average = dogAges.average() (= 6)
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85. Kombination von Operatoren
val oldDogAgeAverage = dogs.map { it.age }.filter { it > 5 }.average()
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86. Hacking
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87. Syntax-Beispiel
Öffne 5_Lambdas.kt
val oldDogAgeAverage = dogs.map { it.age }.filter { it > 5 }.average()
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88. Lösung
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// TODO TASK 1
private fun findDogNames(dogs: List<Dog>): List<String> {
return dogs.map { it.name }
}
// TODO TASK 2
private fun findOldDogs(dogs: List<Dog>): List<Dog> {
return dogs.filter { it.age > 5 }
}
// TODO TASK 3
private fun findNamesOfOldDogs(dogs: List<Dog>): List<String> {
return dogs.filter { it.age > 5 }.map { it.name }
}

89. Mehr Kotlin Features
• Data Klassen (Autogeneriertes Equals, Hashcode & Clone)
• Mutable und Immutable lists
• Destructuring Declarations
• Infix Funktionen
• Extension Properties
• Sealed classes
• Sequences
• Explicit returns
…
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90. Kotlin Workshop (14/15 Dezember)
tiny.cc/kotlin
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