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Free Course

Learn Kotlin

Three tracks from Java-familiar to Kotlin-fluent — null safety, data classes, extension functions, coroutines, and Flow. Google's preferred Android language and a rising server-side language. Free forever. No account.

🕐 ~12 hours3 tracksKotlin 2.xJava background helpful

✅ Kotlin is approachable. If you know Java, Kotlin will feel immediately readable. If you don't, Kotlin's concise syntax and helpful compiler messages make it a good first JVM language. The coroutines track (Advanced) is the steepest part — save it for after you're comfortable with the foundations.

Track 1

Foundations

Variables, null safety, classes, and collections

  • Variables, types, and control flow
  • Null safety: String vs String?, ?. and ?:
  • Classes, data classes, and objects
  • Collections: listOf, mapOf, filter, map
  • Functions: lambdas, higher-order, extension
🕐 ~4 hours5 lessons + quiz
Start Foundations →
Track 2

Practitioner

Sealed classes, scope functions, generics, and OOP

  • Sealed classes and exhaustive when
  • Scope functions: let, run, apply, also, with
  • Generics and variance (out, in)
  • Interfaces, abstract classes, and delegation
  • Object expressions and companion objects
🕐 ~4 hours5 lessons + quiz
Start Practitioner →
Track 3

Advanced

Coroutines, Flow, DSLs, and Kotlin Multiplatform

  • Coroutines: suspend, launch, async/await
  • Structured concurrency and CoroutineScope
  • Flow: cold streams, operators, StateFlow
  • Type-safe DSL builders
  • Kotlin Multiplatform basics
🕐 ~4 hours5 lessons + quiz
Start Advanced →

Practice environment

Run Kotlin in your browser — no installation needed.

Kotlin Playground →