Kotlin for beginners

Transcript

1. Kotlin for beginners
2. https://en.wikipedia.org/wiki/Kotlin_(programming_language) „Kotlin is a cross-platform, statically typed, general-purpose high-level programming language with type inference.”
3. Introduction • Kotlin was created by JetBrains. • It was fi rst released in 2011. • It is now an o ffi cial language for Android development.
4. Introduction • Kotlin was created by JetBrains. • It was fi rst released in 2011. • It is now an o ffi cial language for Android development.
5. Introduction • Kotlin was created by JetBrains. • It was fi rst released in 2011. • It is now an o ffi cial language for Android development.
6. Introduction • Kotlin was created by JetBrains. • It was fi rst released in 2011. • It is now an o ffi cial language for Android development.
7. Pros • Concise and readable code. • Built-in null safety. • Interoperability with Java.
8. Pros • Concise and readable code. • Built-in null safety. • Interoperability with Java.
9. Pros • Concise and readable code. • Built-in null safety. • Interoperability with Java.
10. Pros • Concise and readable code. • Built-in null safety. • Interoperability with Java.
11. Kotlin vs Java fun main(args: Array<String>) { val numbers = listOf(1, 2, 3, 4, 5) val evenNumbers = numbers.filter { it % 2 = = 0 } println(evenNumbers) } import java.util.ArrayList; import java.util.List; import java.util.function.Predicate; public class Main { public static void main(String[] args) { List<Integer> numbers = new ArrayList <> (); numbers.add(1); numbers.add(2); numbers.add(3); numbers.add(4); numbers.add(5); Predicate<Integer> isEven = n - > n % 2 == 0; List<Integer> evenNumbers = new ArrayList <> (); for (int number : numbers) { if (isEven.test(number)) { evenNumbers.add(number); } } System.out.println(evenNumbers); } }
12. Kotlin vs Java fun main(args: Array<String>) { val numbers = listOf(1, 2, 3, 4, 5) val evenNumbers = numbers.filter { it % 2 = = 0 } println(evenNumbers) } import java.util.ArrayList; import java.util.List; import java.util.function.Predicate; public class Main { public static void main(String[] args) { List<Integer> numbers = new ArrayList <> (); numbers.add(1); numbers.add(2); numbers.add(3); numbers.add(4); numbers.add(5); Predicate<Integer> isEven = n - > n % 2 == 0; List<Integer> evenNumbers = new ArrayList <> (); for (int number : numbers) { if (isEven.test(number)) { evenNumbers.add(number); } } System.out.println(evenNumbers); } }
13. Kotlin vs Java fun main(args: Array<String>) { val numbers = listOf(1, 2, 3, 4, 5) val evenNumbers = numbers.filter { it % 2 = = 0 } println(evenNumbers) } import java.util.ArrayList; import java.util.List; import java.util.function.Predicate; public class Main { public static void main(String[] args) { List<Integer> numbers = new ArrayList <> (); numbers.add(1); numbers.add(2); numbers.add(3); numbers.add(4); numbers.add(5); Predicate<Integer> isEven = n - > n % 2 == 0; List<Integer> evenNumbers = new ArrayList <> (); for (int number : numbers) { if (isEven.test(number)) { evenNumbers.add(number); } } System.out.println(evenNumbers); } }
14. Kotlin vs Java
15. ;
17. Hello world fun main() { println("Hello, Kotlin!") }
18. UByte ULong UInt UShort Types Int Byte Short Long
19. UByte ULong UInt UShort Types Int Byte Short Long
20. UByte ULong UInt UShort Types Int Byte Short Long Float Double
21. UByte ULong UInt UShort Types Int Byte Short Long Float Double Char String
22. UByte ULong UInt UShort Types Int Byte Short Long Float Double Boolean Char String
23. UByte ULong UInt UShort Types Int Byte Short Long Float Double Boolean Char String Array
24. Variables val name: String = "John" var isFun: Boolean = true val age: Int = 25
25. Variables val name: String = "John" var isFun: Boolean = true val age: Int = 25 mutable immutable
26. Variables name val name: String = "John" var isFun: Boolean = true val age: Int = 25 mutable immutable
27. Variables name type val name: String = "John" var isFun: Boolean = true val age: Int = 25 mutable immutable
28. Variables name type value val name: String = "John" var isFun: Boolean = true val age: Int = 25 mutable immutable
29. Variables name type value val name = "John" var isFun = true val age = 25 mutable immutable
30. var (mutable) var value: Int = 123 value = 1 value = 332 println(value) // 332
31. val (immutable) val workshop: String = "Kotlin for beginners" workshop = "JS for beginners"
32. val (immutable) val workshop: String = "Kotlin for beginners" workshop = "JS for beginners" val cannot be reassigned
33. Operators + - * / = %
34. Operators + - * / = %
35. Operators
36. Operators == !=
37. Operators == ! = == == !=
38. Operators == ! = == == != > < = > = <
39. Operators == ! && || = == == != > < = > = < !
40. Operators == ! && || = == == != > < = > = < ! is as
41. Now it’s time for you to play with variables.
42. Functions fun sum(a: Int, b: Int): Int { return a + b }
43. Functions fun sum(a: Int, b: Int): Int { return a + b }
44. Functions fun sum(a: Int, b: Int): Int { return a + b } name
45. Functions fun sum(a: Int, b: Int): Int { return a + b } name arguments
46. Functions fun sum(a: Int, b: Int): Int { return a + b } name arguments return type
47. Functions fun sum(a: Int, b: Int) = a + b name arguments return type
48. Functions fun hello(name: String, surname: String): Unit { println("Hello $name $surname") } hello("Bill", "Gates") / / Hello Bill Gates!
49. Functions fun hello(name: String, surname: String): Unit { println("Hello $name $surname") } hello("Bill", "Gates") / / Hello Bill Gates!
50. Named arguments hello("Bill", "Gates") // Hello Bill Gates! hello("Gates", "Bill") // Hello Gates Bill!
51. Named arguments hello(name = "Gates", surname = "Bill") // Hello Gates Bill! hello(surname = "Bill", name = "Gates") // Hello Gates Bill!
52. Now it’s time for you to play with functions.
53. Control fl ows val age = 18 if (age > = 100) { println("This person is really old") } else if (age >= 18) { println("This person is an adult") } else { println("This person is not an adult") }
54. Control fl ows val age = 18 if (age > = 100) { println("This person is really old") } else if (age >= 18) { println("This person is an adult") } else { println("This person is not really old") }
55. Control fl ows val age = 18 if (age > = 100) { println("This person is really old") } else if (age >= 18) { println("This person is an adult") } else { println("This person is not an adult") }
56. Control fl ows val age = 18 when { age > = 100 -> println("Really old adult") age > = 18 -> println("An adult") else -> println("Not an adult") }
57. Control fl ows val age = 18 when (age) { in 0 . . 17 -> println("Not an adult") in 18 .. 99 -> println("An adult") else -> println("Really old adult") }
58. Control fl ows val age = 18 val adultState = when (age) { in 0 . . 17 -> "Not an adult" in 18 .. 99 -> "An adult" else -> "Really old adult" } println(adultState)
59. Loops for (i in 0 . . 50) { // 0 <= i <= 50 println(i) }
60. Loops var i = 0 while (i <= 50) { println(i) i ++ }
61. Now it’s time for you to solve the FizzBuzz problem.
62. Write a program that prints the numbers from 1 to 100. But for multiples of three print "Fizz" instead of the number and for the multiples of fi ve print "Buzz". For numbers which are multiples of both three and fi ve print "FizzBuzz".
63. Null safety ?
64. Null safety val age: Int = null val name: String? = null val length = name.length if (name != null) { val length = name.length }
65. val age: Int = null val name: String? = null val length = name.length if (name != null) { val length = name.length } Null safety
66. val age: Int = null val name: String? = null val length = name.length if (name != null) { val length = name.length } Null safety
67. val age: Int = null val name: String? = null val length = name.length if (name != null) { val length = name.length } Null safety
68. val age: Int = null val name: String? = null val length = name.length if (name != null) { val length = name.length } Null safety
69. val age: Int = null val name: String? = null val length = name.length if (name != null) { val length = name.length } Null safety
70. Null safety !!
71. Null safety val name: String? = JavaLib.getName() val length = name !! .length // throws NullPointerException val length = name ?. length / / returns null val length: String? = name ? . length ?: "" // returns ""
72. Null safety val name: String? = JavaLib.getName() val length = name !! .length // throws NullPointerException val length = name ?. length / / returns null val length: String? = name ? . length ?: "" // returns ""
73. Null safety val name: String? = JavaLib.getName() val length = name !! .length // throws NullPointerException val length = name ?. length / / returns null val length: String? = name ? . length ?: "" // returns ""
74. Null safety ?.
75. Null safety val name: String? = JavaLib.getName() val length = name !! .length // throws NullPointerException val length = name ?. length / / returns null val length: String? = name ? . length ?: "" // returns ""
76. Null safety val name: String? = JavaLib.getName() val length = name !! .length // throws NullPointerException val length: Int? = name ? . length // returns null val length: Int = name ?. length ? : 0 // returns 0
77. Classes class Color( val red: Int, val green: Int, val blue: Int, val alpha: Int, )
78. Classes • Closed by default • Public by default class Color( val red: Int, val green: Int, val blue: Int, val alpha: Int, )
79. Inheritance open class Event class MenuItemSectionClickEvent(val sectionName: String) : Event() class AccountItemClickEvent(val name: String) : Event()
80. Interfaces interface Printable { fun print() }
81. Interfaces class Color( .. . ) : Printable { override fun print() { val hex = String.format("#%02x%02x%02x", red, green, blue) println(hex) } }
82. Special classes • Abstract classes • Data classes • Enum classes • Inline classes • Sealed classes • Object
83. Data classes • data keyword • toString() implementation • equals() / hashcode() implementation • copy() implementation • …
84. Data classes data class Color( val red: Int, val green: Int, val blue: Int, val alpha: Int, )
85. Data classes class Color( val red: Int, ... ) val red = Color(255, 0, 0, 255) println(red) // Color@5679c6c6
86. Data classes data class Color( val red: Int, ... ) val red = Color(255, 0, 0, 255) println(red) // Color(red=255, green=0, blue=0, alpha=255)
87. Enum classes enum class TextAlign { LEFT, RIGHT, CENTER, JUSTIFY, } TextAlign.CENTER
88. Now it’s time for you to play with classes.
89. Collections
90. Collections MutableList<T> MutableSet<T> MutableMap<K, V> List<T> Set<T> Map<K, V>
91. Collections val cipher = arrayOf(50, 51, 89, ... ) val authors = listOf("Bjørn", "Ingrid") val authors = mutableListOf("Bjørn", "Ingrid")
92. Collections val cipher: Array<Int> = arrayOf(50, 51, 89, .. . ) val authors: List<String> = listOf("Bjørn", "Ingrid") val authors: MutableList<String> = mutableListOf("Bjørn", "Ingrid")
93. Collections val mutableAuthors = mutableListOf("Bjørn", "Ingrid") mutableAuthors[1] / / Ingrid mutableAuthors.size // 2 mutableAuthors.add("Stein") / / ["Bjørn", "Ingrid", "Stein"] mutableAuthors.removeAt(1) // ["Bjørn", "Stein"] mutableAuthors.remove("Stein") / / ["Bjørn"]
94. Collection operations data class Student( val name: String, val age: Int, val subjects: List<String>, ) val students = listOf( Student("Alice", 18, listOf("Math", "Computer Science")), ... ) val selectedStudents = students.filter { it.age == 18 } .filter { "Computer Science" in it.subjects } .map { it.name } .onEach { println(it) }
95. Now it’s time for you to play with collections.
96. Additional resource • https://kotlinlang.org/docs/home.html • https://play.kotlinlang.org/koans/overview • https://hyperskill.org/tracks?category=4 • https://kt.academy/book
97. Thank you!