Kotlin was created by JetBrains to improve developer productivity and enjoyment when building tools like IntelliJ IDEA. Some key features of Kotlin include properties, smart casts, extension functions, and null safety. Kotlin works well for server-side development using frameworks like Kara and Exposed, as well as Android development using Android Extensions and Anko. To succeed with Kotlin, developers should take initiative by starting with tests and utilities in existing Java projects rather than waiting for new projects.

1. Kotlin in the CommunityTeam
Productivity Tools
Languages
Kotlin
MPS
TeamCity
YouTrack
Upsource
IDEs
IntelliJ IDEA
PhpStorm
PyCharm
RubyMine
WebStorm
AppCode
CLion
.NET & Visual Studio
developer productivity tools
ReSharper
ReSharper С++
dotCover
dotTrace
dotMemory
dotPeek

2. Kotlin:
Why Do You Care?
Dmitry Jemerov <yole@jetbrains.com>
2

3. 3

4. • Statically typed programming language targeting
the JVM
• Support for functional and OO paradigms
• Pragmatic, safe, concise, great Java interop
• Free and open-source
• In public beta, 1.0 coming Real Soon Now
4

5. Outline
• Why Kotlin was created
• Kotlin feature highlights
• How and why we’re using Kotlin
• Where Kotlin works best
• How you can benefit from Kotlin in your projects
5

6. Why was Kotlin
created?
6

7. “We’ve built tools to support
so many nice languages,
and we’re still using Java”
7
JetBrains, 2010

8. Developer Productivity
8

9. Develop with Pleasure
9

10. Thought Leadership
• Programming languages are a popular discussion
topic
• IntelliJ IDEA is always going to have best support
for Kotlin
10

11. Good chance of success
• Technical: experience building intelligent tools to
support other languages
• Marketing: company reputation and user trust
11

12. Kotlin Feature
Highlights
12

13. Primary Constructor
class Person(val firstName: String,
val lastName: String) {
}

14. Properties
class Person(val firstName: String,
val lastName: String) {
val fullName: String
get() = "$firstName $lastName"
}

15. Properties
class Person(val firstName: String,
val lastName: String) {
val fullName: String
get() = "$firstName $lastName"
}

16. Smart Casts
interface Expr
class Constant(val value: Double) : Expr
class Sum(val op1: Expr, val op2: Expr)
: Expr

17. Smart Casts
fun eval(e: Expr): Double = when(e) {
}

18. Smart Casts
fun eval(e: Expr): Double = when(e) {
}

19. Smart Casts
fun eval(e: Expr): Double = when(e) {
is Constant -> e.value
}

20. Smart Casts
fun eval(e: Expr): Double = when(e) {
is Constant -> e.value
}
class Constant(val value: Double) : Expr

21. Smart Casts
fun eval(e: Expr): Double = when(e) {
is Constant -> e.value
is Sum -> eval(e.op1) + eval(e.op2)
else ->
throw IllegalArgumentException()
}
class Sum(val op1: Expr, val op2: Expr)
: Expr

22. Extension Functions
fun String.lastChar() =
this.get(this.length - 1)
"abc".lastChar()

23. Extension Functions
fun String.lastChar() =
this.get(this.length - 1)
"abc".lastChar()

24. Extension Functions
fun String.lastChar() =
this.get(this.length - 1)
"abc".lastChar()

25. Nullability

26. Nullability
class TreeNode(val parent: TreeNode?,
val left: TreeNode?,
val right: TreeNode?) {
}

27. Nullability
class TreeNode(val parent: TreeNode?,
val left: TreeNode?,
val right: TreeNode?) {
fun depth(): Int {
val parentDepth = if (parent != null)
parent.depth()
else
0
return parentDepth + 1
}
}

28. Nullability
class TreeNode(val parent: TreeNode?,
val left: TreeNode?,
val right: TreeNode?) {
fun depth(): Int {
return (parent?.depth() ?: 0) + 1
}
}

29. Nullability
class TreeNode(val parent: TreeNode?,
val left: TreeNode?,
val right: TreeNode?) {
fun depth(): Int {
return (parent?.depth() ?: 0) + 1
}
}

30. Collections and Lambdas
fun nobleNames(persons: List<Person>)
= persons
.filter { "von " in it.lastName }

31. Collections and Lambdas
fun nobleNames(persons: List<Person>)
= persons
.filter { "von " in it.lastName }

32. Collections and Lambdas
fun nobleNames(persons: List<Person>)
= persons
.filter { "von " in it.lastName }
.sortBy { it.firstName }

33. Collections and Lambdas
fun nobleNames(persons: List<Person>)
= persons
.filter { "von " in it.lastName }
.sortBy { it.firstName }
.map { "${it.firstName} ${it.lastName}” }

34. How JetBrains Uses
Kotlin
34

35. Projects Using Kotlin
• Kotlin
• JetProfile (CRM, sales and license management)
• IntelliJ IDEA 15
• YouTrack v.next
• 2 new unannounced projects
• Research projects related to bioinformatics
• Plugins, Intranet services etc.
35

36. JetProfile
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37. Проект JetProfile
37

38. JetProfile Project
• Started in July 2013
• Replaces old Spring-based system
• 100% Kotlin, 100k LOC
• Team of 6 developers
38

39. IntelliJ IDEA
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40. Kotlin in IntelliJ IDEA
• In tests since version 14, in production since 15
• 74k LOC in Kotlin, out of which 18k in tests
• A few developers actively using Kotlin
• Kotlin team provides support with updating to new
Kotlin versions
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41. Where Kotlin Works
Best

42. The Strengths of Kotlin
• Modeling the data of your application concisely
and expressively
• Creating reusable abstractions using functional
programming techniques
• Creating expressive domain-specific languages

43. Kotlin on the Server Side
• Java interop ensures that all existing Java
frameworks can be used
• No rewrite required to start using Kotlin in existing
codebase
• Existing investment is fully preserved

44. Server-side Kotlin
Frameworks
• Kara: Web framework powering JetProfile
https://github.com/shafirov/kara
• Exposed: Database access framework
https://github.com/JetBrains/exposed
• Ktor: Experimental next generation Web framework
https://github.com/kotlin/ktor

45. Kara: HTML Builders
fun HtmlBodyTag.renderPersonList(
persons: Collection<Person>)
{
table {
for (person in persons) {
tr {
td { +person.name }
td { +person.age }
}
}
}
}
45

46. Kara: HTML Builders
fun HtmlBodyTag.renderPersonList(
persons: Collection<Person>)
{
table {
for (person in persons) {
tr {
td { +person.name }
td { +person.age }
}
}
}
}
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47. Exposed: Table structure
object CountryTable : IdTable() {
val name = varchar("name", 250)
.uniqueIndex()
val iso = varchar("iso", 3)
.uniqueIndex()
val currency = varchar("currency", 3)
}
47

48. Exposed: Entities
class Country(id: EntityID) : Entity(id) {
var name: String by CountryTable.name
val allCustomers by Customer.referrersOn(
CustomerTable.country_id)
}
48

49. Exposed: Queries
val germany = Country
.find { CountryTable.iso eq "de" }
.first()
49

50. Kotlin for Android
• Compatible with Java 6
• Small runtime library
• Great tooling in Android Studio
• Compatible with existing Java libraries and tools
• 100% Java performance

51. Kotlin Tools for Android
• Kotlin Android Extensions: no more findViewById()
• Anko: DSL for UI, extension functions
https://github.com/jetbrains/anko
• KApt: annotation processing

52. Kotlin Android Extensions
import kotlinx.android.synthetic.activity_main.click_me_button
public class MainActivity : Activity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
click_me_button.onClick {
toast("Thank you!")
}
}
}

53. Kotlin Android Extensions
import kotlinx.android.synthetic.activity_main.click_me_button
public class MainActivity : Activity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
click_me_button.onClick {
toast("Thank you!")
}
}
}

54. Kotlin Android Extensions
import kotlinx.android.synthetic.activity_main.click_me_button
public class MainActivity : Activity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
click_me_button.onClick {
toast("Thank you!")
}
}
}

55. Anko: Android UI Builders
tableLayout {
for (location in locations) {
tableRow {
textView(text = location.name)
.lparams(column = 1)
}
}
}

56. Kotlin in the Community

57. How to succeed
with Kotlin
57

58. Take initiative
58

59. Take initiative
• Kotlin is not a silver bullet and not a magical
solution for the problems of your project
• Kotlin makes you more productive and your work
more enjoyable
• Try it and share the results with your teammates
59

60. Don’t wait for a new project
• Kotlin can be easily integrated into existing Java
codebases
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61. Where to start using Kotlin
• Tests - OK not informative
• Plugins and utilities - better
• Core and frameworks - best
61

62. Don’t fear the learning curve
• At JetBrains, summer interns become productive
with Kotlin very quickly and deliver great results
62

63. Use the Java to Kotlin
converter
• Convert only the classes that you’re going to
modify
• Cleanup and refactor the code produced by the
converter
63

64. Use the Java to Kotlin
converter
64

65. Summary
• JetBrains entrusts the most business-critical tasks
to Kotlin
• Kotlin works great for both server-side and Android
development
• Take initiative and start using Kotlin today!
65

67. Q&A
https://kotlinlang.org/
https://try.kotlinlang.org/
@kotlin
yole@jetbrains.com
@intelliyole
67