What You Should Know Now — and What's Next

What You Should Know Now

• Core syntax: val and var, types, string templates, if and when expressions, loops, and ranges
• Null safety: nullable types, safe calls, the Elvis operator, let, and smart casts
• Lists, sets, maps, and the collection functions (map, filter, groupBy, fold) that replace most loops
• Functions with default and named arguments, lambdas, higher-order functions, and extension functions
• Classes, data classes, inheritance, interfaces, objects, enums, and sealed hierarchies
• Generics, scope functions, exceptions, files, Gradle, JSON, and testing
• Coroutines, structured concurrency, and Flow
• Delegation, inline and value classes, and type-safe DSLs
• Android with Jetpack Compose, back ends with Ktor, and sharing code with Kotlin Multiplatform
• Performance, security, and shipping Kotlin to production

What Should You Learn Next?

• Android in depth — Jetpack libraries (Navigation, Room, WorkManager, Hilt), Material Design, and the Android app lifecycle.
• Back-end Kotlin — Spring Boot with Kotlin or Ktor, SQL databases, authentication, and deployment.
• Kotlin Multiplatform — share business logic between Android and iOS, with Compose Multiplatform for shared UI.
• A related language — Java, for reading the huge body of JVM code and libraries Kotlin works with; or Swift, whose ideas (optionals, data types, extensions) map closely onto Kotlin's, if you're heading toward iOS.
• Software design — testing strategies, architecture, and the SOLID principles, which Kotlin's features make easy to apply.

Build Something

Pick a small project you'll actually use — an Android app for a hobby, a command-line tool that automates a chore, a Ktor API for a side project — and finish it, with tests. Shipping one small, complete thing teaches more than starting several big ones.