Kotlin is a statically-typed programming language for the JVM and the browser, built by a team at JetBrains and designed as a pragmatic and easy-to-use Java alternative. In this presentation we'll explore the most notable Kotlin features, such as: - Extension functions - Null-safety - Smart casts - and many more Check out and see that programming in Kotlin is fun!

1. Fun With
Kotlin
by Egor Andreevici

2. INTRO
WHAT’S KOTLIN

3. INTRO
WHY KOTLIN?

4. INTRO
PRAGMATISM
Clarity Safety Interoperability Tooling
WHAT’S KOTLIN ABOUT?

5. INTRO
FOCUS ON USE CASES
INTEROPERATE
WHY PRAGMATIC?

6. INTRO
WHO MAINTAINS KOTLIN?

7. INTRO
WHO’S USING KOTLIN?

8. SYNTAX

9. SYNTAX
fun sum(a: Int, b: Int): Int {
return a + b
}
KOTLIN SYNTAX

10. SYNTAX
fun sum(a: Int, b: Int): Int {
return a + b
}
KOTLIN SYNTAX

11. SYNTAX
fun sum(a: Int, b: Int): Int {
return a + b
}
KOTLIN SYNTAX

12. SYNTAX
fun sum(a: Int, b: Int): Int {
return a + b
}
KOTLIN SYNTAX

13. SYNTAX
fun sum(a: Int, b: Int): Int {
return a + b
}
KOTLIN SYNTAX

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

15. SYNTAX
fun sum(a: Int, b: Int): Int = a + b
KOTLIN SYNTAX

16. SYNTAX
fun sum(a: Int, b: Int) = a + b
KOTLIN SYNTAX

17. CLASSES

18. CLASSES
Kotlin Java
class Person public class Person {}
CREATING A CLASS

19. CLASSES
class Person
class Student : Person()
INHERITANCE

20. CLASSES
class Person
class Student : Person() // won’t compile!
INHERITANCE

21. CLASSES
class Person
class Student : Person() // won’t compile!
INHERITANCE

22. CLASSES
open class Person
class Student : Person() // voila!
INHERITANCE

23. CLASSES
open class Person(val name: String, var age: Int)
// Java
public class Person {
private final String name;
private Integer age;
public Person(String name, Integer age) { // }
public String getName() { // }
public Integer getAge() { // }
public void setAge(Integer age) { // }
}
CONSTRUCTORS

24. CLASSES
open class Person(val name: String, var age: Int)
Kotlin Java
val name: String final String name
var age: Int Integer age
VAL & VAR

25. CLASSES
data class Person(val name: String, var age: Int)
‣ equals() & hashCode() $0
‣ toString() $0
‣ componentN() functions $0
‣ copy() function $0
‣ TOTAL FREE!
DATA CLASSES

26. CLASSES
val name = person.component1()
val age = person.component2()
COMPONENTN() FUNCTIONS

27. CLASSES
val name = person.component1()
val age = person.component2()
for ((name, age) in people) {
println("$name is $age years old")
}
DESTRUCTURING DECLARATIONS

28. CLASSES
class Person {
companion object {
val FIELD_NAME = "name"
fun isOlderThan(person: Person, age: Int) =
person.age > age
}
}
println(Person.isOlderThan(person, 30))
STATIC -> OBJECT

29. CLASSES
public final class StringUtils {
public static String capitalize(String str) {
// TODO: return capitalized string
return str;
}
}
StringUtils.capitalize(“a”);
UTILS IN JAVA

30. CLASSES
fun String.capitalize(): String {
// TODO: return capitalized string
return this
}
"a".capitalize()
EXTENSIONS IN KOTLIN

31. CLASSES
fun String.capitalize(): String {
// TODO: return capitalized string
return this
}
"a".capitalize()
import me.egorand.kotlin.extensions.capitalize
EXTENSIONS IN KOTLIN

32. NULL-SAFETY

33. NULL-SAFETY
THE BILLION DOLLAR MISTAKE

34. NULL SAFETY
var a: String = "abc"
a = null // compilation error
var b: String? = "abc"
b = null // OK
val l = a.length
val l = b.length // error: variable 'b' can be null
NULLABLE VS NON-NULL TYPES

35. NULL SAFETY
val l = if (b != null) b.length else -1
CHECKING FOR NULL: SIMPLE APPROACH

36. NULL SAFETY
b?.length
bob?.department?.head?.name
CHECKING FOR NULL: SAFE CALLS

37. NULL SAFETY
CHECKING FOR NULL: ELVIS OPERATOR

38. NULL SAFETY
val l: Int = if (b != null) b.length else -1
val l = b?.length ?: -1
CHECKING FOR NULL: ELVIS OPERATOR

39. NULL SAFETY
val l = b!!.length()
CHECKING FOR NULL: LIVING DANGEROUSLY

40. FUNCTIONS

41. FUNCTIONS
fun double(x: Int): Int {
return x * 2
}
val result = double(2)
FUNCTIONS IN KOTLIN

42. FUNCTIONS
fun Int.times(n: Int) = this * n
println(2.times(3))
INFIX NOTATION

43. FUNCTIONS
infix fun Int.times(n: Int) = this * n
println(2.times(3))
INFIX NOTATION

44. FUNCTIONS
infix fun Int.times(n: Int) = this * n
println(2 times 3)
INFIX NOTATION

45. FUNCTIONS
fun printString(str: String,
prefix: String = "",
postfix: String = "") {
println(prefix + str + postfix)
}
printString("hello")
printString("hello", "<")
printString("hello", "<", ">")
DEFAULT ARGUMENTS

46. FUNCTIONS
fun printString(str: String,
prefix: String = "",
postfix: String = "") {
println(prefix + str + postfix)
}
printString(“hello”,
prefix = “<“,
postfix = “>”)
NAMED ARGUMENTS

47. FUNCTIONS
fun <T> forEach(list: List<T>, f: (T) -> Unit) {
for (elem in list) {
f(elem)
}
}
val list = listOf("Alice", "Bob", "Claire")
forEach(list, ::println)
forEach(list, { str -> println(str) })
HIGHER-ORDER FUNCTIONS

48. FUNCTIONS
fun <T> forEach(list: List<T>, f: (T) -> Unit) {
for (elem in list) {
f(elem)
}
}
val list = listOf("Alice", "Bob", "Claire")
forEach(list, ::println)
forEach(list, { println(it) })
HIGHER-ORDER FUNCTIONS

49. FUNCTIONS
fun <T> forEach(list: List<T>, f: (T) -> Unit) {
for (elem in list) {
f(elem)
}
}
val list = listOf("Alice", "Bob", "Claire")
forEach(list, ::println)
forEach(list) { println(it) }
HIGHER-ORDER FUNCTIONS

50. SMART CASTS

51. SMART CASTS
// Java
private static void demo(Object x) {
if (x instanceof String) {
String str = (String) x;
System.out.println(str.length());
}
}
CASTING IN JAVA

52. SMART CASTS
// Java
private static void demo(Object x) {
if (x instanceof String) {
String str = (String) x;
System.out.println(str.length());
}
}
// Kotlin
fun demo(x: Any) {
if (x is String) {
println(x.length)
}
}
SMART CASTS IN KOTLIN

53. SMART CASTS
fun demo(x: Any) {
if (x is String) {
println(x.length)
}
}
IF EXPRESSION

54. SMART CASTS
fun demo(x: Any) {
if (x !is String) {
println("Not a String")
} else {
println(x.length)
}
}
IF-ELSE EXPRESSION

55. SMART CASTS
fun demo(x: Any) {
if (x !is String) return
println(x.length)
}
RETURN STATEMENT

56. SMART CASTS
if (x !is String || x.length == 0) return
if (x is String && x.length > 0)
print(x.length)
BOOLEAN EXPRESSIONS

57. WHAT’S NEXT?

58. WHAT’S NEXT?
POST-1.0 ROADMAP
▸ New language features
▸ Java 8/9 support
▸ JavaScript support
▸ Android tooling improvements
▸ IDE features

59. WHAT’S NEXT?
RESOURCES
▸ Kotlin - http://kotlinlang.org/
▸ Koans - http://try.kotlinlang.org/koans
▸ Blog - https://blog.jetbrains.com/kotlin/
▸ Forum - https://devnet.jetbrains.com/community/kotlin
▸ Slack - http://kotlinlang.slack.com/

60. Thank you!
@EgorAnd
+EgorAndreevich
http://blog.egorand.me/