Kotlin or The Quest For Java.Next

A lot of people in the Java community has been long longing for some kind of a "Java.Next" language, a language that will be modern yet keep the design spirit. There is a lot of more or less suitable candidates -- let's take a brief look at some of them and then examine Kotlin in more detail. Kotlin comes from JetBrains, a company with more than 10 years of experience developing industry-leading developer tools and therefore pretty unique perspective on language design. We'll take a look at some of the more interesting features: null-safety and other nice little things in the type system, language-supported delegation, lambdas, extension methods and DSL support. Few words about Java interop too.

Transcript

1. Kotlin or The Quest For Java.Next lthon@redhat.com
2. Java.Next ? ? ?
3. JRuby? Jython? Groovy?
4. Clojure?
5. Gosu? Fantom? Mirah?
6. Scala?
7. Ceylon?
8. Xtend?
9. Kotlin?
10. Java 8?
11. Java 8!
12. However...
13. I think that Kotlin is a pretty good one
14. kotlin.jetbrains.org kotlin-demo.jetbrains.com
15. Hello, world! package _01hello fun main(args: Array<String>) { println("Hello, world!") }
16. Classes package _02classes class Person1(name: String) { val name: String { this.name = name } }
17. Classes package _02classes class Person2(name: String) { val name: String = name }
18. Classes package _02classes class Person3(val name: String) fun main(args: Array<String>) { val person = Person3("Ladislav Thon") println(person) }
19. Classes package _02classes data class Person4(val name: String) fun main(args: Array<String>) { val person = Person4("Ladislav Thon") println(person) }
20. Traits package _03traits trait Foo { fun foo(): String } trait Bar { fun bar() = "bar" }
21. Traits package _03traits class Fubar : Foo, Bar { override fun foo() = "foo" fun fubar() { println("${foo()}-${bar()}") } }
22. Multiple Inheritance? • single inheritance + interfaces ◦ Java <= 7, C# • stateless traits ◦ Kotlin, Ceylon, Java 8 (kind of…) • stateful traits ◦ PHP >= 5.4 (I think…) • mixins ◦ Scala, Dart • full multiple inheritance ◦ C++
23. Null Safety & Smart Casts package _04nullSafety fun main(args: Array<String>) { val maybeAnswer: Int? = ... if (maybeAnswer != null) { val answer: Int = maybeAnswer } }
24. Null Safety & Safe Navigation & Elvis package _04nullSafety fun main(args: Array<String>) { val answer: Int? = … val doubleAnswer = answer?.let { it * 2 } answer?.times { println("Hi!") } val question = answer ?: 42 }
25. Collections package _05collections fun print(nums: Collection<Number>) { println(nums) } fun add(nums: MutableCollection<Int>) { nums.add(4) }
26. Generics package _06generics trait Producer<out T> { fun produce(): T } trait Consumer<in T>{ fun consume(t: T) }
27. Generics package _06generics trait Holder<T> { fun produce(): T fun consume(t: T) } fun use(h: Holder<out String>) { h.produce() }
28. Extension Methods package _07extensions fun String.pirateStyle() = "Arrr! ${this.capitalize()}" fun main(args: Array<String>) { println("hello, world".pirateStyle()) }
29. Lambdas package _08lambdas fun main(args: Array<String>) { val nums = arrayListOf(1, 2, 3, 4, 5, 6, 7) .filter { it % 2 == 0 } .flatMap { listOf(it, it * 2, it * 3) } .takeWhile { it < 10 } println(nums) }
30. Lambdas package _08lambdas fun Lock.locked<T>(compute: () -> T): T { this.lock() try { return compute() } finally { this.unlock() } }
31. Delegation package _09delegation class MyList<T>(val l: List<T>) : List<T> by l fun main(args: Array<String>) { val list = MyList<String>(listOf("a, b, c")) list.forEach { println(it) } }
32. Delegation package _09delegation class LazyString { val value: String by Delegates.lazy { println("heavy computation") "the string!" } }
33. Builders & DSL support package _10builders fun data(build: Data.() -> Unit): Data { val result = Data() result.build() return result }
34. kotlin.jetbrains.org kotlin-demo.jetbrains.com
35. ? http://devconf.cz/f/83 lthon@redhat.com