![44
Collections
// immutable list
val list = listOf("a", "b", "c","aa")
list.filter { it.startsWith("a") }
// immutable map
val map = mapOf("a" to 1, "b" to 2, "c" to 3)
for ((k, v) in map) {
println("$k -> $v")
}
// mutable map
val map2 = HashMap<String,String>()
// direct map access
map2["a"] = "my value"
println(map2["a"])
// range
for (i in 1..100) { //... }](https://image.slidesharecdn.com/kotlinsmarterdevelopmentforthejvm-161205084213/85/Kotlin-smarter-development-for-the-jvm-44-320.jpg)
![45
InterOp
object UserSingleton{
fun stringify(user : User) : String{
val (name,age) = user
return "[name=$name][age=$age]"
}
}
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){
println("Hello ${user.name}")
}
}
}
User u = new User("toto",42);
User.Companion.sayHello(u);
UserUtilsKt.WhatIsyourAge(u);
System.out.println("stringify : "+UserSingleton.INSTANCE.stringify(u));
Kotlin code
Calling Kotlin from Java](https://image.slidesharecdn.com/kotlinsmarterdevelopmentforthejvm-161205084213/85/Kotlin-smarter-development-for-the-jvm-45-320.jpg)
Kotlin, smarter development for the jvm
- 1. Smarter development for the JVM #GeekBreakFast Kotlin
- 2. @arnogiu Work @ ekito App & Gear Maker Mobile & Cloud DevArnaud GIULIANI
- 5. 5 The new « Swift » for Android ? https://goo.gl/W5g6Do - mid 2014
- 6. Limits of java - Verbose - Type inference - No properties / Lazy / Delegate - Checked exception - NullPointerException - Extensibility - End of lines with ; https://goo.gl/HIrmC9 @sdeleuze
- 7. But Java is great … - Fast - Optimized bytecode - Static typing - Simple to learn - Amazing ecosystem
- 10. (not only) Functional programming First class functions, immutability, no side effects, conciseness …
- 12. How K can help you ? - Conciseness - Null Safety & Immutability protection - Static Typing & Smart Casts - Open programming styles (lambdas, high order functions …) - Java interop
- 13. What’s Kotlin ? - Fully open source (built by Jetbrains) - Run on Java 6+ - Static typing & type inference - Modern language features - 1st grade tooling
- 14. What’s inside 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
- 15. 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
- 16. Use Cases Source : poll on Kotlin Slack (early 2016)https://goo.gl/HIrmC9 @sdeleuze
- 17. 17 Want some nougat ?
- 19. 19
- 20. 20 is Kotlin Android friendly ? https://github.com/SidneyXu/AndroidDemoIn4Languages Method counts by Language
- 21. Where to use Kotlin ?* *everywhere you use Java
- 22. 22 let’s go write some Kotlin !
- 23. Ready to use Easy to run
- 24. 24 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" } 1.0.5-2 also available with maven
- 25. 25 IntelliJ
- 26. 26
- 27. 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
- 29. 29 Typing & Inference val a: Int = 1 val b = 1 // `Int` type is inferred var x = 5 // `Int` type is inferred x += 1 Infered values Mutable values val : constant value - IMMUTABLE var : variable value - MUTABLE USE VAL AS MUCH AS POSSIBLE !
- 30. 30 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
- 31. 31 Late initialization, Lazy, Delegates … // 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 !!.
- 32. 32 Example
- 33. 33 Class class User ( var userName: String, var firstName: String, var lastName: String, var location: Point? = null ) POJO + - Getter - Setter - Constructors
- 34. 34 Data Class data class User ( var userName: String, var firstName: String, var lastName: String, var location: Point? = null ) POJO + - Getter - Setter - Constructors - toString - hashcode - equals - copy
- 35. 35 POJO ?
- 36. 36 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 // customer getter & setter var stringRepresentation: String get() = this.toString() set(value) { setDataFromString(value) // parses the string and assigns values to other properties } class ApiKey(var weatherKey: String, var geocodeKey: String){ var debug : Boolean = false }
- 37. 37 Object Component // singleton object Resource { val name = "Name" } println(" my resource is : ${Resource.name}") class StringCalculator{ // class helper companion object{ val operators = arrayOf("+","-","x","/") } } println(" my operators are : ${StringCalculator.operators}") Singleton Class Companion Object
- 38. 38 Example data class User(val name: String = "", val age: Int = 0) val jack = User(name = "Jack", age = 1) val anotherJack = jack.copy(age = 2) json class data class usage
- 39. 39 When when (s) { 1 -> print("x == 1") 2 -> print("x == 2") else -> { // Note the block print("x is neither 1 nor 2") } } Flow Control (replace your old if blocks) when (x) { in 1..10 -> print("x is in the range") in validNumbers -> print("x is valid") !in 10..20 -> print("x is outside the range") else -> print("none of the above") } Pattern Matching in <range> -> is <type> -> expression -> when (s) { is String -> print("s is a string") else -> print("s is not a string") }
- 40. 40 Example
- 41. 41 Functions fun reformat(str: String, normalizeCase: Boolean = true, upperCaseFirstLetter: Boolean = true, wordSeparator: Char = ' '): String { } Named Parameters & default values reformat(str, true, true, '_') // old way to call reformat(str, wordSeparator = '_') // using default values & named params fun String.hello(): String = "Hello " + this val hi = "Arnaud !".hello() println("$hi") // Hello Arnaud ! Extension
- 42. 42 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). numberString.split("n").flatMap { it.split(separator) } .map(Integer::parseInt) .map(::checkPositiveNumber) .filter { it <= 1000 } .sum()
- 43. 43 Destructuring Data fun extractDelimiter(input: String): Pair<String, String> = … val (separator, numberString) = extractDelimiter(input) data class User(var name : String,var age : Int) val toto = User("toto",42) val (name,age) = toto Returning two values with Pair Destructured values with data classes
- 44. 44 Collections // immutable list val list = listOf("a", "b", "c","aa") list.filter { it.startsWith("a") } // immutable map val map = mapOf("a" to 1, "b" to 2, "c" to 3) for ((k, v) in map) { println("$k -> $v") } // mutable map val map2 = HashMap<String,String>() // direct map access map2["a"] = "my value" println(map2["a"]) // range for (i in 1..100) { //... }
- 45. 45 InterOp object UserSingleton{ fun stringify(user : User) : String{ val (name,age) = user return "[name=$name][age=$age]" } } 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){ println("Hello ${user.name}") } } } User u = new User("toto",42); User.Companion.sayHello(u); UserUtilsKt.WhatIsyourAge(u); System.out.println("stringify : "+UserSingleton.INSTANCE.stringify(u)); Kotlin code Calling Kotlin from Java
- 46. Sweet stuffs for
- 47. 47 Kotlin’s Android Extensions android { ... sourceSets { main.java.srcDirs += 'src/main/kotlin' } } apply plugin: 'com.android.application' apply plugin:‘kotlin-android’ apply plugin:‘kotlin-android-extensions’ // if use extensions In your build.gradle
- 48. Kotlin Java
- 49. Anko - Android DSL Async task in few lines doAsync { // Long background task uiThread { result.text = "Done" } } Layout DSL verticalLayout { val name = editText() button("Say Hello") { onClick { toast("Hello, ${name.text}!") } } } https://github.com/Kotlin/anko
- 51. One of our longest journey …
- 53. 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
- 56. 56 Just another hype JVM stuff ?
- 57. 57 Ready to go ?
- 59. 59 Always hard to start …
- 60. 60 Our feedback with K - Easy to start small & grow (no big bang) - Tool support is very good - Great feedback about the language itself - Stable in production ! - Magical conversion … but take care - Hard to come back to java …
- 61. 61 IF YOU DON'T LOOK AT JAVA AND THINK, "THIS COULD BE BETTER", DON'T SWITCH. @RunChristinaRun
- 63. 63 Try Kotlin online http://try.kotlinlang.org/#/Examples/ Kotlin Reference https://kotlinlang.org/docs/reference/ Kotlin Cheat Sheet (by ekito) http://www.slideshare.net/arnaudgiuliani/kotlin- cheat-sheet-by-ekito Kotlin Community https://kotlinlang.org/community.html
- 64. 64 Kotlin 1.1
- 65. Thank you :)