A modern JVM language by JetBrains — concise, null-safe, and the official language of Android. Java's spiritual successor without the verbosity.
← Back to Server SideString can't be null; String? can.data class Customer(val name: String, val age: Int) { fun isAdult() = age >= 18 } val adults = customers .filter { it.isAdult() } .sortedBy { it.name } // Coroutines — async without callback hell suspend fun loadUser(id: Int): User = httpClient.get("/api/users/$id").body()
Billion-dollar mistake fixed at the type level. val name: String? is nullable; you must use ?., ?:, or !! to access it. Compiler enforced.
Lightweight suspending functions for async work. Flow is Kotlin's reactive streams API. Cleaner than RxJava, simpler than callbacks.
Add methods to types you don't own. fun String.isEmail() = … lets every String have .isEmail() — without subclassing.
| Category | Tools |
|---|---|
| Build | Gradle (Kotlin DSL), Maven |
| Backend | Spring Boot (Kotlin support), Ktor, Micronaut, Quarkus |
| Android | Jetpack Compose, AndroidX |
| Multiplatform | KMP, Compose Multiplatform |
| Test | JUnit 5, Kotest, MockK |
The Google-blessed default; Jetpack Compose is Kotlin-native.
Spring Boot or Ktor with much less boilerplate than Java.
Share business logic across iOS & Android via KMP.
Adopt incrementally — file by file inside a Java codebase.