Kotlin Workshop

Workshop about the basics of Kotlin. We loved the language from the start and switched all of our projects to Kotlin in 2017.

Transcript

1. Kotlin für Android/Java- Entwickler Malte Bucksch 1
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 Malte Bucksch 2
3. Wieso Kotlin? Concise Safe Inter- operable Malte Bucksch 3
4. Anwendungsgebiete JVM Android Browser Native Malte Bucksch 4
5. Firmen, die Kotlin nutzen Evernote Malte Bucksch 5
6. Java-to-Kotlin Converter Malte Bucksch 6
7. Setup Malte Bucksch 7
8. Setup https://github.com/quickbirdstudios/KotlinBasics 1 2 3 Malte Bucksch 8
9. Just say NO Malte Bucksch 9
10. Setup app\src\test\java\com\quickbirdstudios\kotlinbasics\exercises Malte Bucksch 10
11. Hacking Führe alle Tests aus und stell sicher, dass alle Tests fehlschlagen Run Tests in ‘exercises’ Rechtsklick… Malte Bucksch 11
12. Malte Bucksch 12
13. Bruno Malte Bucksch 13
14. Variablen und Konstanten Malte Bucksch 14
15. String myVariable = "Change me"; final String myConstant = "Can't change me"; var myVariable: String = "Change me“ val myConstant: String = "Can't change me" 15
16. String myVariable = "Change me"; final String myConstant = "Can't change me"; var myVariable: String = "Change me“ val myConstant: String = "Can't change me" 16
17. final String myConstant = "Can't change me"; String myVariable = "Change me"; val myConstant = "Can't change me" var myVariable = "Change me" 17
18. Funktionen Malte Bucksch 18
19. Funktionen fun bark(times: Int): String { return "Wuff".repeat(times) } Function Keywort Return Typ Malte Bucksch 19
20. Funktionen fun bark(times: Int = 1): String { return "Wuff".repeat(times) } Standard-Wert Malte Bucksch 20
21. Funktionen fun bark(times: Int = 1) = "Wuff".repeat(times) Malte Bucksch 21
22. Aufrufen von Funktionen dog.bark() dog.bark(3) dog.bark(times = 3) Malte Bucksch 22
23. Klassen Malte Bucksch 23
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") } } 24
25. Kotlin Klasse class KotlinHuman(var name: String, var age: Int) { fun sayHello(otherPersonName: String = "") { println("Hi, nice to see you $otherPersonName") } } Primary Constructor Malte Bucksch 25
26. Kotlin Klasse class KotlinHuman(var name: String, var age: Int) { fun sayHello(otherPersonName: String = "") { println("Hi, nice to see you $otherPersonName") } } String template Malte Bucksch 26
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") } } Malte Bucksch 28
28. Zugriff auf Properties Malte Bucksch 29 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") } } Malte Bucksch 30
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") } } Malte Bucksch 31
31. Instantierung von Klassen val myKotlinHuman = KotlinHuman("Bruno",5) Kein “new” Keywort mehr Malte Bucksch 33
32. Hacking Malte Bucksch 36
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 Malte Bucksch 37
34. Lösung Malte Bucksch 38 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 Malte Bucksch 39
36. Nullpointer exceptions public void sayHello(Dog otherDog){ System.out.println(“Wuff, "+ otherDog.getName()); } sayHello(null); Malte Bucksch 40
37. Kotlin Null-Sicherheit fun sayHello(otherDog: Dog) { println("Hi, " + dog.name); } sayHello(null); Malte Bucksch 41
38. Compiler Error. var dog: Dog = null Malte Bucksch 42
39. Optionals als seperater Typ var dog: Dog? = null Malte Bucksch 43
40. Aufrufen von Kotlin Optionals val dog: Dog? = findDog() dog.bark() Malte Bucksch 44
41. Aufrufen von Kotlin Optionals val dog: Dog? = findDog() if(dog != null){ dog.bark(3) } Malte Bucksch 45
42. Safe Call Operator val dog: Dog? = findDog() dog?.bark() Malte Bucksch 46
43. For all NPE lovers val dog: Dog? = findDog() dog!!.bark() Malte Bucksch 47
44. Elvis Operator val myDog = findDog() ?: buyNewDog() Malte Bucksch 48
45. Automatic casting if(dog != null){ dog.bark(3) } val anyObject: Any = getAnimal() if(anyObject is Dog){ anyObject.bark() } Malte Bucksch 49
46. Hacking Malte Bucksch 50
47. Syntax-Beispiel Öffne 2_Optionals.kt human?.sayHello() val myDog = findDog() ?: buyNewDog() // Safe casts val name = (any as? Cat)?.name Malte Bucksch 51
48. Lösung Malte Bucksch 52 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 Malte Bucksch 53
50. For Schleife Malte Bucksch 54 val dogs = getDogs() for (dog in dogs){ dog.bark() }
51. For Schleife Malte Bucksch 55 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" } } Malte Bucksch 56
53. When: Java Switch mit Superkräften fun getDogPluralString(dogCount: Int): String { when(dogCount){ 0 -> return "Keine Hunde" 1 -> return "Ein Hund" else -> return "$dogCount Hunde" } } Malte Bucksch 57
54. When: Java Switch mit Superkräften fun getDogPluralString(dogCount: Int): String { return when(dogCount){ 0 -> "Keine Hunde" 1 -> "Ein Hund" else -> "$dogCount Hunde" } } Malte Bucksch 58
55. When: Java Switch mit Superkräften fun getDogPluralString(dogCount: Int) = when (dogCount) { 0 -> "Keine Hunde" 1 -> "Ein Hund" else -> "$dogCount Hunde" } Malte Bucksch 59
56. When ohne Argument fun evaluatePassword(password: String): String { return when { password.isEmpty() -> "Bitte gib ein Passwort ein" password.length < 5 -> "Passwort ist nicht lang genug" !password.containsNumber() -> "Passwort muss eine Ziffer enthalten" else -> "Das Passwort ist valide" } } Malte Bucksch 60
57. Hacking Malte Bucksch 61
58. Syntax-Beispiel Öffne 3_ControlFlow.kt when(dogCount){ 0 -> return "Keine Hunde" 1 -> return "Ein Hund" else -> return "$dogCount Hunde" } return when (dogCount) { in 0..4 -> "..." 4, 5 -> "..." else -> "..." } Malte Bucksch 62
59. Lösung Malte Bucksch 63 // 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 Malte Bucksch 64
61. println("Ich heiße Bruno".barkify()) // “WUFF WUFF WUFF” Malte Bucksch 65
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 Malte Bucksch 66
63. Hacking Malte Bucksch 67
64. Syntax-Beispiel Öffne 4_Extensions.kt fun Int.isEven(): Boolean { return this % 2 == 0 } Malte Bucksch 68
65. Lösung Malte Bucksch 69 // 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 Malte Bucksch 70
67. Lambda Funktionsreferenz val dog = Dog("Bruno") val bark = dog::bark bark(times = 3) Malte Bucksch 71
68. Lambda Definition val dog = Dog("Bruno") val greetDog: (Dog) -> String = { dog -> "Hey! ${dog.name}" } println(greetDog(dog)) Parameter type Return type Malte Bucksch 72
69. Lambda Definition val dog = Dog("Bruno") val greetDog: (Dog) -> String = { dog -> "Hey! ${dog.name}" } println(greetDog(dog)) Parameter name Lambda Body Malte Bucksch 73
70. Higher Order Functions: Filter Malte Bucksch 74
71. Filtern von Hunden Malte Bucksch 75
72. Filter Funktion var dogs: List<Dog> = animals.filter( … ) Malte Bucksch 76
73. Filter Prädikat/Bedingung { animal -> animal is Dog } ? ? Malte Bucksch 77
74. Filter Funktion var dogs = animals.filter({ animal -> animal is Dog }) Malte Bucksch 78
75. Filter Funktion var dogs = animals.filter(){ animal -> animal is Dog } Malte Bucksch 79
76. Filter Funktion var dogs = animals.filter { animal -> animal is Dog } Malte Bucksch 80
77. Filter Funktion var dogs = animals.filter { it is Dog } Malte Bucksch 81
78. Higher Order Functions: Map Malte Bucksch 82
79. Mapping von Hunden age = 8 age = 2 age = 3 age = 6 age = 11 age = 8 age = 2 age = 3 age = 6 age = 11 Malte Bucksch 83
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 { … } Malte Bucksch 84
81. Map Prädikat/Bedingung { dog -> dog.age } age = 8 age = 8 Malte Bucksch 85
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 } Malte Bucksch 86
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 } Malte Bucksch 87
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) Malte Bucksch 88
85. Kombination von Operatoren val oldDogAgeAverage = dogs.map { it.age }.filter { it > 5 }.average() Malte Bucksch 89
86. Hacking Malte Bucksch 90
87. Syntax-Beispiel Öffne 5_Lambdas.kt val oldDogAgeAverage = dogs.map { it.age }.filter { it > 5 }.average() Malte Bucksch 91
88. Lösung Malte Bucksch 92 // 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 … Malte Bucksch 93
90. Kotlin Workshop (14/15 Dezember) tiny.cc/kotlin Malte Bucksch 94