Ever wonder what this "new" Kotlin thing is? Curious what the syntax looks like? Unsure how to implement this at your own company? Or do you just want to know what Nick and Cody's favorite things are about this language? All that and (maybe) more are revealed in Privet Kotlin.

1. Privet Kotlin

2. Hello Kotlin

3. Hello Kotlin
Cody Engel
Senior Software Engineer @ Yello
Free T-Shirts & Clean Code
Nick Cruz
Android Engineer @ Yello
Mr. Plantastic & Crispy Animations

4. 2. Getting Started
3. Null Safety
4. Our Favorite Things About Kotlin
5. Kotlin At Work
1. Fun Facts

5. 2. Getting Started
3. Null Safety
4. Our Favorite Things About Kotlin
5. Kotlin At Work
1. Fun Facts

6. Developed in 2011 by JetBrains
(IntelliJ IDEA, RubyMine, PhpStorm, Android Studio)
Released 2012
Statically typed programming language
for the JVM

7. Developed in 2011 by JetBrains
(IntelliJ IDEA, RubyMine, PhpStorm)
Released 2012
Statically typed programming language
for the JVM

8. Runs on JVM = 100% Interoperability with Java

11. 2. Getting Started
3. Null Safety
4. Our Favorite Things About Kotlin
5. Kotlin At Work
1. Fun Facts

12. 1. Fun Facts
3. Null Safety
4. Our Favorite Things About Kotlin
5. Kotlin At Work
2. Getting Started

13. Functions

14. sum( , b:Int) {
return a + b
}
fun a: Int : Int
Functions

15. Functions
sum( , b:Int) {
return a + b
}
fun a: Int : Int

16. Functions
sum( , b:Int) {
return a + b
}
fun a: Int : Int

17. Functions
sum( , b:Int) {
return a + b
}
fun a: Int : Int

18. Functions
sum( , b:Int) {
return a + b
}
fun a: Int : Int

19. Functions
sum( , b:Int) {
return a + b
}
fun a: Int : Int

20. fun sum(a: Int, b: Int) = a + b
Functions

21. Functions
fun printSum(a: Int, b: Int): Unit {
println("sum of $a and $b is ${a + b}")
}

22. fun printSum(a: Int, b: Int) {
println("sum of $a and $b is ${a + b}")
}
Functions

23. Variables

24. val immutable: Int = 1
Variables

25. val immutable = 2
Variables

26. val immutable: Int
immutable = 3
Variables

27. var mutable = 0
mutable++
mutable++
Variables

28. Properties

29. class Address {
var name: String = ...
var street: String = ...
var city: String = ...
var state: String? = ...
var zip: String = ...
}
Properties

30. fun copyAddress(address: Address): Address {
val result = Address()
result.name = address.name
result.street = address.street
return result
}
Properties

31. val isEmpty: Boolean
get() = this.size == 0
Properties

32. var stringRepresentation: String
get() = this.toString()
set(value) {
field = value.toString()
}
Properties

33. String Templates

34. val = "Java"
println(
String.format("The way is terrible!", )
)
java
java%s
String Templates

35. String Templates
val = "Java"
println(
String.format("The way is terrible!", )
)
java
java%s

36. val = "Kotlin"
println("The way is awesome!")
kotlin
$kotlin
String Templates

37. String Templates
val = "Kotlin"
println("The way is awesome!")
kotlin
$kotlin

38. Control Flow

39. var max = a
if (a < b) max = b
Control Flow - If Expression

40. var max: Int
if (a > b) {
max = a
} else {
max = b
}
Control Flow - If Expression

41. val max = if (a > b) a else b
Control Flow - If Expression

42. val max = if (a > b) {
print("Returns a")
a
} else {
print("Returns b")
b
}
Control Flow - If Expression

43. when (x) {
1 -> print("x == 1")
2 -> print("x == 2")
else -> {
print(“x is neither 1 nor 2")
}
}
When Expression - Replaces Switch

44. when (x) {
1, 2 -> print("x == 1 or a == 2")
else -> print(“x is neither 1 nor 2”)
}
When Expression - Replaces Switch

45. when (x) {
in 1..10 -> print("x is in the range")
in validNumbers -> print("x is valid")
!in 10..20 -> print("x is outside the range")
else -> print("none of the above")
}
When Expression - Replaces Switch

46. when {
x.isOdd() -> print("x is odd")
x.isEven() -> print("x is even")
else -> print("x is funny")
}
When Expression - Replaces If/Else If

47. for (item in collection) {
print(item)
}
For Loops

48. for (i in array.indices) {
print(array[i])
}
For Loops

49. for ((index, value) in array.withIndex()) {
println("the element at $index is $value")
}
For Loops

50. 2. Getting Started
3. Null Safety
4. Our Favorite Things About Kotlin
5. Kotlin At Work
1. Fun Facts

51. 1. Fun Facts
2. Getting Started
4. Our Favorite Things About Kotlin
5. Kotlin At Work
3. Null Safety

52. Null Safety
(and Immutability)

53. Caused by: java.lang.NullPointerException: Attempt
to invoke virtual method 'java.lang.String
java.lang.String.trim()' on a null object
reference

54. Nullable String s; val s: String?
NonNull String s; val s: String

57. val length = s!!.length
NonNull Assert

58. val length = s!!.length
NonNull Assert
kotlin.KotlinNullPointerException
at part2.delegation.interceptor.LoggerList.add(LoggerList.kt:39)
(don’t do this)

59. val length = s!!.length
val length = s?.length // Int?
NonNull Assert
Safe call, returns optional
kotlin.KotlinNullPointerException
at part2.delegation.interceptor.LoggerList.add(LoggerList.kt:39)
(don’t do this)

60. val length = s?.length ?: 0 // Int
Safe Call and Elvis Operator

61. val length = s?.length ?: 0 // Int
Safe Call and Elvis Operator
Other helpful operators
with, apply, let, run
s?.let {
val length = it.length // Int
// Do stuff with length
}

62. What about variables that become null?
What about variables that become non-null?

63. Mutable
Nullable
String s; var s: String?
Mutable
NonNull
String s; var s: String
Immutable
Nullable
final String s; val s: String?
Immutable
NonNull
final String s; val s: String

64. 2. Getting Started
3. Null Safety
4. Our Favorite Things About Kotlin
5. Kotlin At Work
1. Fun Facts

65. 1. Fun Facts
2. Getting Started
3. Null Safety
5. Kotlin At Work
4. Our Favorite Things About Kotlin

66. Classes

67. Data Classes
We frequently create classes whose main purpose is to
hold data. In such a class some standard functionality
and utility functions are often mechanically derivable
from the data. In Kotlin, this is called a data class.

68. Data Classes
data class User(val name: String, val age: Int)

69. data class User(
val name: String = "",
val age: Int = 0
)
Data Classes

70. val user = User(“Jane Smith", 27)
user.name
user.age
user.toString()
user.hashCode()
user.equals()
Data Classes

71. val jack = User(name = "Jack", age = 1)
val olderJack = jack.copy(age = 2)
Data Classes

72. val jane = User("Jane", 35)
val (name, age) = jane
println("$name, $age years of age")
Data Classes

73. Sealed Classes
Sealed classes are used for representing restricted
class hierarchies, when a value can have one of the
types from a limited set, but cannot have any other type.
They are, in a sense, an extension of enum classes: the
set of values for an enum type is also restricted, but
each enum constant exists only as a single instance,
whereas a subclass of a sealed class can have multiple
instances which can contain state.

74. sealed class Expr {
data class Const(val number: Double) : Expr()
data class Sum(val e1: Expr, val e2: Expr) : Expr()
object NotANumber : Expr()
}
Sealed Classes

75. Sealed Classes
fun eval(expr: Expr): Double = when(expr) {
is Const -> expr.number
is Sum -> eval(expr.e1) + eval(expr.e2)
NotANumber -> Double.NaN
}

76. Lambdas
& Higher-Order Functions

77. A higher-order function is a function
that takes functions as parameters,
or returns a function.
fun transform1Through5(transform: (Int) -> Int) {
for (int in 1..5) {
println(transform(int))
}
}

78. fun transform1Through5(transform: (Int) -> Int) {
for (int in 1..5) {
println(transform(int))
}
}
Method Reference
class NumberDoubler {
fun run(int: Int) = int * 2
}
fun doubleNumbersMethodReference() {
val numberDoubler = NumberDoubler()
transform1Through5(numberDoubler::run)
}

79. Lambda
fun transform1Through5(transform: (Int) -> Int) {
for (int in 1..5) {
println(transform(int))
}
}
fun doubleNumbersLambda() {
transform1Through5 { num -> num * 2 }
}

80. transform1Through5 { num -> num * 2 }

81. transform1Through5 { it * 2 }

82. transform1Through5 { it * 3 }

83. transform1Through5 { it * 30 }

84. transform1Through5 { it * it }

85. listOf(1, 2, 3, 4, 5)
.filter { it % 2 == 1 } // Filter evens: [1, 3, 5]
.map { it * 2 } // Double the results: [2, 6, 10]
.forEach { println(it) } // Print them
Kotlin Collections

86. listOf(1, 2, 3, 4, 5)
.filter { it % 2 == 1 } // Filter evens: [1, 3, 5]
.map { it * 2 } // Double the results: [2, 6, 10]
.forEach { println(it) } // Print them
Kotlin Collections
Observable.just(1, 2, 3, 4, 5)
.filter { it % 2 == 1 }
.map { it * 2 }
.forEach { println(it) }
RxJava Observable (in Kotlin)

87. 2. Getting Started
3. Null Safety
4. Our Favorite Things About Kotlin
5. Kotlin At Work
1. Fun Facts

88. 1. Fun Facts
2. Getting Started
3. Null Safety
4. Our Favorite Things About Kotlin
5. Kotlin At Work

89. @

90. Introduce Kotlin
@

91. Introduce Kotlin
• Discuss the benefits of Kotlin.
• Give snippets in Pull Request comments.
• Get others on our team interested.
@

92. Learn Together
@

93. Learn Together
• Work through Kotlin Koans together.
• Watch Kotlin videos together.
• Make this a team effort.
@

94. Kotlin In Production
@

95. Kotlin In Production
• Determine code style rules as a team.
• Find the path of least resistance.
• Java-style Kotlin in the beginning.
• Focus on continuous improvement.
@

96. twitter.com/POTUS404
medium.com/@CodyEngel
github.com/CodyEngel github.com/NickCruz
medium.com/@NickCruz26
twitter.com/ReactiveNick
medium.com/yello-offline
instagram.com/yello_offline
twitter.com/yello_offline

97. Resources
Kotlin Koans
https://goo.gl/MTLEYg
KotlinLang
https://kotlinlang.org
Life is Great and Everything Will Be Ok, Kotlin Is Here
https://goo.gl/yhp2Gn
Kotlin Uncovered
https://goo.gl/fbAFW5
Introduction To Kotlin
https://goo.gl/iCwYHd