Kotlin - Not you grandfather's Java

Introduction to Kotlin, for Java developers.

Presented on March 30th 2017 for the Portuguese Java User Group, at Talkdesk's Lisbon Office.

Transcript

1. Kotlin:
   Not your grandfather’s Java
   João Carvalho - @johnkarva - PT.JUG
   

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5. What is Kotlin?
   

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8. https://try.kotlinlang.org
   

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9. Philosophy
   

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10. Pragmatic
    

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11. Concise
    

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12. Safe
    

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13. Interoperable
    

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14. Tooling
    

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15. Lightweight
    868KB runtime
    

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17. public class HelloWorld {
    public static void main(String... args) {
    System.out
    .println("Hello world " + args[0]);
    }
    }
    

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18. fun main(args: Array) {
    println("Hello world ${args[0]}")
    }
    

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19. Types
    

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20. public void printName(Person person) {
    System.out.println(person.getName());
    }
    

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21. public void printName(Person person) {
    System.out.println(person.getName());
    }
    null
    

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23. fun printName(person: Person) {
    println(person.name)
    }
    

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24. printName(null)
    ERROR: Null cannot be a value of
    non-null type Person.
    

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25. fun printName(person: Person?) {
    if (person != null) {
    println(person.name)
    }
    }
    

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26. Primitive Types
    

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27. Arrays
    

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28. Variables
    

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29. final String name = "Kotlin";
    int age = 5;
    // A few moments later
    age = 6;
    

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30. val name: String = "Kotlin"
    var age: Int = 5
    // A few moments later
    age = 6
    

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31. val name = "Kotlin"
    var age = 5
    // A few moments later
    age = 6
    

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32. Functions/Expressions
    

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33. fun max(one: Int, other: Int): Int {
    if (one > other) {
    return one
    } else {
    return other
    }
    }
    

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34. fun max(one: Int, other: Int): Int {
    return if (one > other) {
    one
    } else {
    other
    }
    }
    

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35. fun max(one: Int, other: Int): Int =
    if (one > other) {
    one
    } else {
    other
    }
    

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36. fun max(one: Int, other: Int) =
    if (one > other) {
    one
    } else {
    other
    }
    

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37. fun max(one: Int, other: Int) =
    if (one > other) one else other
    

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38. Operators
    

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39. when (x) {
    1 -> print("x == 1")
    2 -> print("x == 2")
    else -> {
    print("x is neither 1 nor 2")
    }
    }
    

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40. Safe Navigation
    

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41. private String safeGetName(Person person) {
    return person == null ? null :
    person.getName();
    }
    

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42. fun safeGetName(person: Person?): String? {
    return person?.name
    }
    

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43. Elvis Operator
    

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44. fun printName(person: Person?) {
    println("Name is ${person?.name
    ?: "Unknown"}")
    }
    

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45. Smart Casts
    

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46. fun printStringLength(any: Any) {
    if (any is String) {
    println("Length is ${any.length}")
    } else {
    return println("Oops, not a String")
    }
    }
    

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47. fun printStringLength(any: Any) {
    val asString = any as String
    println("Length is ${asString.length}")
    }
    

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48. fun printStringLength(any: Any) {
    val asString = any as? String
    println("Length is ${asString?.length
    ?: "Unknown"}")
    }
    

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49. Classes
    

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50. class Person {
    }
    

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51. Final/Public by default
    

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52. Constructors
    

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53. class Fooer(name: String) {
    init {
    println("Setting up to foo $name")
    }
    }
    

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54. class Fooer(name: String) {
    init {
    println("Setting up to foo $name")
    }
    constructor(name: String, option: String) : this(name) {
    println("\tUsing option $option")
    }
    }
    

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55. Inheritance
    

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56. open class Bar
    class Foo : Bar() {
    }
    

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57. Properties
    

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58. class Fooer(name: String) {
    private val name: String
    init {
    this.name = name
    }
    }
    

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59. class Fooer(private val name: String)
    

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60. private var name: String = ""
    get() {
    println("Returning $name")
    return name
    }
    

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61. var name: String = ""
    private set
    

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62. Delegated Properties
    

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63. class Example {
    var p: String by Delegate()
    }
    

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64. val lazyValue: String by lazy {
    println("computed!")
    "Hello"
    }
    

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65. var name: String by
    Delegates.observable("") {
    _, old, new ->
    println("$old -> $new")
    }
    

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66. Extension Functions
    

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67. fun String.helloize() = "Hello $this"
    "World".helloize()
    

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68. Data classes
    

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69. public class Person {
    private String name;
    private int age;
    (...)
    }
    

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70. public Person(String name, int age) {
    this.name = name;
    this.age = age;
    }
    

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71. public String getName() {
    return name;
    }
    public void setName(String name) {
    this.name = name;
    }
    

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72. @Override
    public boolean equals(Object o) {
    (Stuff generated by your IDE)
    }
    @Override
    public int hashCode() {
    int result = name.hashCode();
    result = 31 * result + age;
    return result;
    }
    

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73. @Override
    public String toString() {
    return "Person{" +
    "name='" + name + '\'' +
    ", age=" + age +
    '}';
    }
    

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75. data class Person(var name: String,
    var age: Int)
    

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76. val john = Person("John", 21)
    

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77. Immutable?
    

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78. private final String name;
    public Person withName(String name) {
    return new Person(name, this.age);
    }
    

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79. data class Person(var name: String,
    var age: Int)
    

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80. data class Person(val name: String,
    val age: Int)
    

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81. val john = Person("John", 21)
    val olderJohn = john.copy(age = 78)
    

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82. Named Arguments
    

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83. public class Person {
    public Person(String name,
    String lastName,
    int age,
    Instant birthDate,
    (...))
    }
    

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84. new Person("John", "Doe",
    26, Instant.now(), (...));
    

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86. Person(name = "John",
    lastName = "Doe",
    age = 26,
    birthDate = Instant.now())
    

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87. Default Values
    

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89. class BCryptPasswordEncoder(
    private val strength: Int = -1,
    private val random: SecureRandom = SecureRandom()
    )
    

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90. Collections
    

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91. Mutable vs Immutable
    

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92. emptyList()
    listOf(1, 2, 3)
    mutableListOf(1, 2, 3)
    emptySet()
    setOf("John", "Jane")
    mutableSetOf("John", "Jane")
    emptyMap()
    mapOf("John" to "Doe")
    mutableMapOf("John" to "Doe")
    

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93. Utilities
    

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94. // apply
    BaseClientDetails().apply {
    clientId = "foo"
    }
    // takeIf
    userRepository.findOne("foo")?.takeIf(User::active)
    // use
    inputStream.use {
    it.read()
    }
    // let
    clientId?.let { loadClient(it) }
    

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95. Going Functional
    

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96. Higher-Order Functions
    

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97. fun doWithinLock(lock: Lock,
    body: () -> T): T {
    lock.lock()
    try {
    return body()
    }
    finally {
    lock.unlock()
    }
    }
    

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98. doWithinLock(lock) {
    println("Hello lock")
    }
    

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99. map.map { (key, value) ->
    "$key$value"
    }
    

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100. Functions with Receiver
     

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101. class HTML {
     var value = ""
     fun body(value: String) { this.value = value }
     }
     fun html(init: HTML.() -> Unit) = HTML().apply {
     init()
     }
     html {
     body("Hello world")
     }
     

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102. Questions?
     

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