Kotlin Path — 9 courses · 650 lessons

The Kotlin learning path

A guided route from beginner to advanced across every Kotlin course: begin with the language tour, go deep with the Deep Dive, sharpen your craft with Patterns & Refactoring, and finish with reactive systems. Follow the recommended order — or jump to what you need.

Foundations

104 lessons

Kotlin — Language Tour

Start here. The syntax and everyday idioms — values, functions, classes, null-safety, collections, lambdas — enough to read and write real Kotlin.

Start

Core mastery

47 lessons

Kotlin — Deep Dive

Go below the syntax: how types, expressions, OOP, generics, coroutines and the type system actually work — with inline visualizations and runnable practice.

Start

Craft — design & quality

52 challenges

Design Patterns in Kotlin

The GoF catalogue + SOLID, retold idiomatically with objects, sealed types and DSLs. Practised as graded Arena challenges.

Practise in Arena

51 challenges

Refactoring Masterclass

Martin Fowler's refactoring catalogue with progressive step hints — turn smelly code into clean Kotlin, one behaviour-preserving move at a time.

Practise in Arena

Advanced — reactive systems

118 lessons

Coroutines — from the machine to production

Coroutines as their own subject, with no framework in the way: what suspend compiles to, scopes and cancellation, composition, channels, Flow, hot state, testing with virtual time, and the production footguns. Every exercise runs against the real kotlinx.coroutines.

Start

78 lessons

Reactive — Reactor · Coroutines · WebFlux · Flow

The reactive stack as it appears in production: Project Reactor, the coroutine bridge, Spring WebFlux + DI, advanced pipelines, and modern Coroutine Flow — modelled on a real vehicle-import service.

Start

Apply — platform & interop

28 lessons

Kotlin ↔ Java Interop

Mix Kotlin and Java in one codebase: nullability & platform types, @JvmStatic / @JvmOverloads / @JvmName, SAM conversions, and calling each language from the other.

Start

24 lessons

Android with Kotlin

Kotlin on Android — the core ideas and patterns, level by level, with annotated code you can read and mark complete.

Start

Backend — Spring Boot & Gradle

148 lessons

Kotlin + Spring Boot (with Gradle)

Build real backends: the Gradle task graph, Spring IoC/DI & beans, REST controllers & services, data repositories, testing. Every Spring challenge embeds a hand-rolled mini-Spring so your @Service/@RestController code actually wires and runs.

Start

Open Arena Data-structure drills Playground Kotlin game Back to Developer Hub