Kotlin
The language we use the most here — from fundamentals to Spring Boot, coroutines and Reactor.
Courses & tools
Kotlin & Coroutines CourseKotlin Deep Dive — MasterclassReactive Kotlin — Reactor, Coroutines & WebFluxKotlin + Spring BootKotlin + Spring Boot 4Design Principles & SOLIDKotlin PersistenceKotlin TestingJackson with KotlinKotlin Java InterOpKotlin CoroutinesKotlin Coroutines & ReactiveGradle for KotlinKotlin — Design Patterns MasterclassKotlin — Refactoring MasterclassKotlin — The Interview RoundKotlin Spring Boot — The Interview RoundKotlin · HackerRank-style algorithmsKotlin — Coroutine drills (extra practice)Kotlin — Reactor operator drills (extra practice)Reactor Flux — Complete GuideCoding ChallengesProject Reactor ChallengesSpring Reactive ProgrammingTrack your Kotlin progress
Practice & prepare for interviews
Complete challenge collections. Choose a topic to see every exercise.
🥋 Kotlin Kombat — stdlib & idiom recall29 challenges Kotlin · HackerRank-style algorithms101 challenges Kotlin — Algorithms & Systems32 challenges Kotlin — Reactor operator drills (extra practice)32 challenges ★ Kotlin · Reactor — Operator Interview62 challenges ★ Kotlin · Reactor — Operator Mastery30 challenges ★ Kotlin — Fun & Games51 challenges Kotlin — Spring Boot drills (extra practice)22 challenges Gradle — lessons + drills11 challenges Kotlin — The Interview Round (predict, run, explain)16 challenges Kotlin Spring Boot — The Interview Round (what Spring does to your objects)7 challenges Kotlin — Coroutines drills (extra practice)40 challenges ★ Kotlin Coroutines — the course (graded practice)118 challenges ★ Kotlin — Coroutines for real (kotlinx + virtual time)17 challenges ★ Kotlin · Reactor ↔ Coroutines — the interop bridge9 challenges ★ Kotlin · Reactor — Lifecycle, resources & the rest of the vocabulary10 challenges Kotlin — Concurrency Interview Pack7 challenges Kotlin — Threads, Locks & Mutex12 challenges Kotlin — Interview Q&A Pack (junior → senior)40 challenges Kotlin — Data-Manipulation Interview Pack28 challenges ★ Kotlin — Stdlib Mastery26 challenges Kotlin — Flow Semantics & Senior Idioms6 challenges