Kotlin, a modern language for modern times
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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.
Kotlin, a modern language for modern times
- 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!
- 4. A language created by JetBrains
- 6. Kotlin/JVM
- 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 }
- 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)