-
Concise
Drastically reduce the amount of boilerplate code.
See example -
Safe
Avoid entire classes of errors such as null pointer exceptions.
See example -
Interoperable
Leverage existing libraries for JVM, Android and the browser.
See example -
Tool-friendly
Choose any Java IDE or build from the command line.
See example
Statically typed programming language
for modern multiplatform applications
for modern multiplatform applications
100% interoperable with Java™ and Android™
Try Kotlin
Build Applications For
Why Kotlin?
Concise
Create a POJO with getters, setters, equals(), hashCode(), toString() and copy() in a single line:
data class Customer(val name: String, val email: String, val company: String)
Or filter a list using a lambda expression:
val positiveNumbers = list.filter { it > 0 }
Want a singleton? Create an object:
object ThisIsASingleton {
val companyName: String = "JetBrains"
}
Safe
Get rid of those pesky NullPointerExceptions, you know, The Billion Dollar Mistake
var output: String
output = null // Compilation error
Kotlin protects you from mistakenly operating on nullable types
val name: String? = null // Nullable type
println(name.length()) // Compilation error
And if you check a type is right, the compiler will auto-cast it for you
fun calculateTotal(obj: Any) {
if (obj is Invoice)
obj.calculateTotal()
}
Interoperable
Use any existing library on the JVM, as there’s 100% compatibility, including SAM support.
import io.reactivex.Flowable
import io.reactivex.schedulers.Schedulers
Flowable
.fromCallable {
Thread.sleep(1000) // imitate expensive computation
"Done"
}
.subscribeOn(Schedulers.io())
.observeOn(Schedulers.single())
.subscribe(::println, Throwable::printStackTrace)
Target either the JVM or JavaScript. Write code in Kotlin and decide where you want to deploy to
import kotlin.browser.window
fun onLoad() {
window.document.body!!.innerHTML += "<br/>Hello, Kotlin!"
}
Tooling
A language needs tooling and at JetBrains, it's what we do best!
Simplest Version
An “Object-oriented” Hello
Android Activity
HTML Builder
What does it look like?
Concise, simple and very easy to read (and write)
package hello
Optional package header
fun main(args: Array<String>) {
Package-level function, which takes an Array
of strings as a parameter
println("Hello World!")
}
Have you noticed?
Semicolons are optional
Semicolons are optional
Class with a primary constructor and a member function
class Greeter(val name: String) {
fun greet() {
println("Hello, $name")
}
}
String Interpolation to cut down ceremony.
fun main(args: Array<String>) {
Greeter(args[0]).greet()
}
Note that there's no new keyword
used to create an object
Type-safe access to views
import kotlinx.android.synthetic.main.activity_main.fab
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
...
fab.setOnClickListener {
Lambdas for concise event handlers
toast("Hello!")
}
Terse wrappers for common Android APIs
}
}
val data = mapOf(1 to "one", 2 to "two")
createHTML().table {
for ((num, string) in data) {
Iterate over data
tr {
Functions to create HTML tags
td { +"$num" }
td { +string }
}
}
}
Outputting variable values
Try Kotlin
Try online
Explore Kotlin code samples and solve problems
directly in the browser
directly in the browser
Latest version: 1.1.2-2
Kotlin Usage Highlights
Pinterest has successfully introduced Kotlin into their application, used by 150M people every month.
Gradle
Gradle is introducing Kotlin as a language for writing build scripts.
Evernote
Evernote recently integrated Kotlin into their Android client
Uber
Uber team uses Kotlin for building internal tools
Corda
is an open-source distributed ledger platform, supported by major banks, and built entirely in Kotlin.
Coursera
Coursera Android app is partially written in Kotlin
Pivotal
Spring makes use of Kotlin's language features to offer more concise APIs
Atlassian
All new code in the Trello Android app is in Kotlin.