Kotlin is a fully interoperable programming language for building Android and multiplatform applications. It is statically typed, concise, and designed to interoperate seamlessly with Java. Kotlin aims to combine the best of both object-oriented and functional programming, and provides features to write safer and more concise code compared to Java, such as null safety, type inference, and extension functions. The document provides an overview of Kotlin's features and how it compares to other languages like Java and Swift, and demonstrates how to set up a Kotlin project using Gradle build system.

1. Develop your next app with
Kotlin

2. @arnogiu
Work @ ekito
Core & Gear Maker
Mobile & CloudArnaud GIULIANI

3. « production ready »
15.02.2016

4. 1.1.1 @ 15.03.2017

5. Yet another JVM
Language ?

6. The new « Swift »
for Android ?
https://goo.gl/W5g6Do - mid 2014

7. Limits of java
- Verbose
- Type inference
- No properties / Lazy / Delegate
- Checked exception
- NullPointerException
- Extensibility
- End of lines with ;
@
sdeleuze

8. But Java is great …
- Fast
- Optimized bytecode
- Static typing
- Simple to learn
- Amazing ecosystem

10. - Conciseness & Smarter API
- Null Safety & Immutability protection
- Type Inference, Static Typing & Smart Casts
- Open programming styles
- Java Interop
Why
Kotlin ?

11. What’s
Kotlin ?
- Fully open source (built by Jetbrains)
- Based on Java & run on Java 6+
- Modern language features
- 1st grade tooling

12. More About
Kotlin …
- String templates
- Properties
- Lambdas
- Data class
- Smart cast
- Null safety
- Lazy property
- Default values for function
parameters
- Extension Functions
- No more ;
- Single-expression
functions
- When expression
- let, apply, use, with
- Collections
- Android Extensions Plugin

13. Compare with
Same conciseness and expressive code, but
Kotlin static typing and null-safety make a big
difference.
"Some people say Kotlin has 80% the power of
Scala, with 20% of the features" *
"Kotlin is a software engineering language in
contrast to Scala which is a computing science
language." *
Swift and Kotlin are VERY similar. Swift is LLVM
based and has C interop while Kotlin is JVM based
and has Java interop.
* Quotes from Kotlin:TheYing andYang of Programming Languages
@
sdeleuze

14. is Kotlin Android friendly ?
https://github.com/SidneyXu/AndroidDemoIn4Languages
Method counts by Language

15. Java 8 on
Android ?
https://android-developers.googleblog.com/2017/03/future-of-java-8-language-feature.html

16. KOTLIN is not just about writing
your app with lesser lines.
It’s all about writing
SAFER & BETTER APPS !

17. Kotlin clearly considered
by the Java community !
https://spring.io/blog/2017/01/04/introducing-kotlin-support-in-
spring-framework-5-0
http://www.javamagazine.mozaicreader.com/
#&pageSet=5&page=0&contentItem=0 (March/April
2017)
https://www.thoughtworks.com/radar/languages-and-frameworks/kotlin

18. Ready to use
Easy to run

19. Getting started with
gradle
buildscript {
ext.kotlin_version = '<version to use>'
dependencies {
classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
}
}
apply plugin: "kotlin"
dependencies {
compile "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
}

20. Gradle tips for Kotlin
# Gradle
org.gradle.jvmargs=-Xmx2048m -XX:MaxPermSize=512m -XX:
+HeapDumpOnOutOfMemoryError -Dfile.encoding=UTF-8
org.gradle.parallel=true
org.gradle.deamon=true
# Kotlin
kotlin.incremental=true
# Android Studio 2.2+
android.enableBuildCache=true
In your gradle.properties
https://medium.com/keepsafe-engineering/kotlin-vs-java-compilation-speed-e6c174b39b5d#.k44v7axsk

21. Let’s go !

22. Typing & Inference
val a: Int = 1
val b = 1 // `Int` type is inferred
var x = 5 // `Int` type is inferred
x += 1
Inferred values
Mutable values
val : constant value - IMMUTABLE
var : variable value - MUTABLE
USE VAL AS MUCH AS POSSIBLE !

23. Safety with Optionals
var stringA: String = "foo"
stringA = null //Compilation error - stringA is a String (non optional)
var stringB: String? = "bar" // stringB is an Optional String
stringB = null //ok
Optional value with ?

24. // set length default value manually
val length = if (stringB != null) stringB.length else -1
//or with the Elvis operator
val length = stringB?.length ?: -1
DefaultValue & Elvis Operator :?
val length = stringB.length // Compilation error - stringB can be null !
// use ? the safe call operator
val length = stringB?.length //Value or null - length is type Int?
val length = stringB!!.length //Value or explicit throw NPE - length is type Int
Safe call with ?. or Explicit call with !!.

25. Example
Working with optional values

26. Example
Null check safety & Smart cast
Securing with default values

27. Class
class User (
val userName: String,
val firstName: String,
val lastName: String,
var location: Point? = null
)
POJO +
- Getter
- Setter
- Constructors

28. Data Class
data class User (
val userName: String,
val firstName: String,
val lastName: String,
var location: Point? = null
)
POJO +
- Getter
- Setter
- Constructors
- toString
- hashcode
- equals
- copy

29. POJO ?
Kotlin
Java

30. Properties
// readonly property
val isEmpty: Boolean
get() = this.size == 0
Properties can be declared in constructor or in class
You can also handle getter & setter
lateinit var weatherWS :WeatherWS
@Test
fun testMyWeatherWS() {
weatherWS = Inject.get<WeatherWS>()
// ...
}
class ApiKey(var weatherKey: String, var geocodeKey: String){
var debug : Boolean = false
}
Late & Lazy initialization

31. Example
data class User(val name: String = "", val age: Int = 0)
val jack = User(name = "Jack", age = 1) //no new keyword
val anotherJack = jack.copy(age = 2)
Data Class usage
A simple GSon Class

32. Object Class
// singleton
object Resource {
val name = "Name"
}
class StringCalculator{
// class helper
companion object{
val operators = arrayOf("+","-","x","/")
}
}
Singleton Class
Companion Object

33. When
when (s) {
1 -> print("x == 1")
2 -> print("x == 2")
else -> { // Note the block
print("x is neither 1 nor 2")
}
}
Flow Control (replace your switch and if-blocks)
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")
}
Pattern Matching

34. Example
Page Adapter
Menu Select

35. Collections
// immutable map
val map = mapOf("a" to 1, "b" to 2, "c" to 3)
for ((k, v) in map) {
println("$k -> $v")
}
map["a"] = "my value" // direct map access with array style
// range
for (i in 1..100) { //... }
// immutable list
val list = listOf("a", "b", "c","aa")
list.filter { it.startsWith("a") }
* collections operators : map, filter, take, flatMap, forEach, firstOrNull, last …

36. Example
Kotlin Collection
Java 7 Collection

37. Lambdas
val fab = findViewById(R.id.fab) as FloatingActionButton
fab.setOnClickListener { view -> popLocationDialog(view) }
A lambda expression or an anonymous function is a “function literal”, i.e. a function that is
not declared, but passed immediately as an expression
- A lambda expression is always surrounded by curly braces
- Its parameters (if any) are declared before -> (parameter types may be omitted),
- The body goes after -> (when present).
myNumber.split("n").flatMap { it.split(separator) }
.map(Integer::parseInt)
.map(::checkPositiveNumber)
.filter { it <= 1000 }
.sum()
* Method references are not surrounded by curly braces !

38. Functions
fun reformat(str: String,
normalizeCase: Boolean = true,
upperCaseFirstLetter: Boolean = true,
wordSeparator: Char = ' '): String {
}
Named Parameters & default values
reformat(str, true, true, '_') // old way to call
reformat(str, wordSeparator = '_') // using default values & named params

39. Extensions Functions
Extension declaration
Usage

40. Destructuring Declarations
In lambdas, Since Kotlin 1.1
map.mapValues { (key, value) -> "$value!" }
Destructured variables declaration
val person = Person("john",31) //data class Person(val name:String, val age : Int)
val (name,age) = person
println("I'm $name, my age is $age")
* Works with Map, Data Class, Pair,Triple …
=> you can return 2 values in function !

41. InterOp Kotlin/Java
Java
Kotlin

42. InterOp Java/Kotlin
object UserSingleton{
fun stringify(user : User) : String{
// …
}
}
fun WhatIsyourAge(user : User){
println("Your age is ${user.age}")
}
data class User (val name: String, val age : Int){
companion object{
fun sayHello(user : User){
//…
}
}
}
User u = new User("toto",42);
User.Companion.sayHello(u);
UserUtilsKt.WhatIsyourAge(u);
UserSingleton.INSTANCE.stringify(u)

43. Sweet stuffs for

44. Kotlin’s Android
Extensions
apply plugin: 'com.android.application'
apply plugin:‘kotlin-android’
apply plugin:‘kotlin-android-extensions’ // the kotlin-android extension !
In your build.gradle

45. Kotlin
Java

46. Reactive
Programming

47. Lamba expressions
Functional Programming
Reactive Streams
http://reactivex.io/documentation/operators.html
http://www.reactive-streams.org/
https://spring.io/blog/2016/06/07/notes-on-reactive-
programming-part-i-the-reactive-landscape

48. Example - Rx/Retrofit
Kotlin
Java 7

49. Example - Rx/Realm
Load first element & update UI

50. 50
Ready to Go ?

51. 51
Just another hype
JVM stuff ?

52. 52
Production
ready ?

53. It’s always hard to start !

54. Our feedback
- Easy to start on existing project
- Great learning curve
- Good doc & tools support
- Don’t use anymore Butterknife, Dagger …
- T_T hard to come back to Java
https://www.ekito.fr/people/kotlin-in-production-one-year-later/

55. IF YOU DON'T LOOK AT
JAVA AND THINK, "THIS
COULD BE BETTER", DON'T
SWITCH.
@RunChristinaRun (Pinterest)

57. Try Kotlin online
http://try.kotlinlang.org/#/Examples/
Kotlin Reference
https://kotlinlang.org/docs/reference/
Kotlin Cheat Sheet (by ekito)
https://speakerdeck.com/agiuliani/kotlin-cheat-
sheet

58. 70% Less !
Develop a
weather app with K
https://github.com/Ekito/2017-handson-kotlinAndroid

59. Thank you :)