HowToCodePage

Kotlin

The modern default language for Android.

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This course has 3 lessons. Start with the first one and use the next / previous links at the bottom of each lesson — the sidebar keeps the whole course in order.

Lessons

  1. Syntax and null safetyvals and vars, expression-oriented control flow, and the type system that keeps null out of your code until you ask for it.
  2. Classes, data classes and extensionsPrimary constructors, inheritance and interfaces, then the language features that remove boilerplate: data classes, sealed types and extension functions.
  3. Coroutines and collectionsSuspend functions without blocking a thread, structured concurrency, Flow for streams, and the collection operators you will use daily.

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Last refreshed 2026-09-17.