This is my talk "Develop your next app with kotlin" for AndroidMakersFr 2017 - Paris

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 :)