Kotlin is a programming language created by JetBrains that runs on the JVM and JavaScript. It is a modern language that aims to interoperate well with Java code and improve on Java in several ways, such as by avoiding null references and supporting features like lambdas. The document provides examples of how Kotlin code compares to Java code for tasks like defining functions and classes, handling null values, using streams and lambdas. It also includes a code sample that transforms a list of keyword strings.

1. Kotlin
A modern language for modern times

2. About me
My name is Sergi
20 years playing with computers
I work at
I add bugs to the Android app
We use Kotlin, and we love it!

3. What is Kotlin?

4. A language created by JetBrains

5. Three flavors

6. Kotlin/JVM

7. Kotlin/Native (beta)

8. Kotlin/Javascript

9. Variables

10. var name = "John"
var surname: String = "Doe"
var address: Location = Location("my house")
name = "Mike"
surname = "Magic"
address = Location("my other house")
val age = 32
age += 1 //Error: is val

11. Nullability

12. var title: String = "Jaws"
title = null //Error: not nullable
var title: String? = "E.T."
genre = null //Fine, name is nullable

13. Java
String lowercase = null
if (uppercase != null) {
lowercase = uppercase.toLowerCase()
}
Kotlin
var lowercase: String? = null
lowercase = uppercase?.toLowerCase()

14. Java
if (session.getLoggedCandidate() != null) {
...do a lot of stuff
}
Kotlin
session.loggedCandidate?.let {
...do a lot of stuff
}

15. Functions & classes

16. class Person (
val name: String,
val surName: String,
var age: Int,
val address: Address?
) {
val fullName = "$name $surName"
fun grow(years: Int = 1) {
age += years
}
fun getNationality() = address?.country
}

17. data class Person(
val name: String,
val surName: String,
var age: Int,
val address: Address?
)
fun brother(person:Person, brotherName: String) =
person.copy(name = brotherName)

18. Lambdas & function type

19. Java
public interface Callback {
void onFinish(String result);
}
public void operation(Callback callback) {
//perform operation
callback.onFinish(result);
}
operation(new Callback() {
@Override
public void onFinish(String result) {
//Do finishing stuff
}
});

20. Kotlin
fun operation(callback: (String) -> Unit) {
//perform operation
callback("")
}
operation { result ->
//finish it
}

21. Streams

22. Java 7
List<Person> grow(List<Person> persons) {
for (Person person : persons) {
person.setAge(person.getAge()+1);
}
}
Java 8
List<Person> grow(List<Person> persons) {
return persons.stream()
.map (person -> person.setAge(person.getAge()+1))
.toList()
}
Kotlin
fun grow(persons: List<Person>) = persons.map { it.age +1 }

23. Real case
Transform this:
"(JAVA OR J2EE OR JAVA2E OR JAVA2EE OR JEE) AND (DESARROLLADOR OR DEVELOPER OR PROGRAMADOR OR PROGRAMMER) AND (SISTEMAS OR
SISTEMES)",
"java or j2ee",
"Java",
"Android",
"(JAVA OR J2EE OR JAVA2EE OR JEE OR JAVA2E) AND (PROGRAMADOR OR PROGRAMMER OR DEVELOPER OR DESARROLLADOR)"
Into this:
"java", "J2EE", "JAVA2E", "JAVA2EE", "JEE", "DESARROLLADOR", "DEVELOPER", "PROGRAMADOR", "PROGRAMMER", "SISTEMAS", “SISTEMES",
"android"
private fun mapKeywords(keywords: List<String>) = keywords
.map { it.split(Regex("( AND )|( OR )|(|)| |,|¿|"|'")) }
.flatten()
.filter { it.isNotBlank() }
.distinctBy { it.toLowerCase() }

24. And much more!
(but we are out of time)

25. More info
https://kotlinlang.org
https://jetbrains.com
https://play.kotlinlang.org/koans (Kotlin Koans)
https://antonioleiva.com/ (buy his book!)
If you have any question: @sergiandreplace
(and I’ll be around the hackathon)