Kotlin 2025 Curriculum: Where to Start Learning the Language

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Kotlin 2025 Learning Plan: where to start and how not to quit

Kotlin is rapidly conquering the development world: from Android apps to server-side solutions and multiplatform projects. If you decide to master this language in 2025, it's important not just to take a course, but to build a systematic learning plan. We have prepared a roadmap that will help a beginner go from setting up the environment to the first commercially viable project.

1. Syntax basics and tooling (1–2 weeks)

Start by installing IntelliJ IDEA Community Edition — the best IDE for Kotlin. Dedicate the first days to:

Variables: val (immutable) and var (mutable), data types (Int, String, Boolean, Double).
Conditional operators if, when (replacement for switch).
Loops for, while, do-while and working with ranges (1..10).
Functions: declaration, arguments, return values, lambdas.
Null Safety: operators ?., ?:, !! — a key Kotlin feature.

Practice with tasks on Codewars or LeetCode (level 8–7 kyu).

2. Object-Oriented Programming (2–3 weeks)

Kotlin is a fully object-oriented language, but with concise syntax. Study:

Classes, constructors (primary and secondary), properties.
Inheritance, interfaces, abstract classes.
Data class — automatic generation of equals/hashCode/toString.
Object and companion object (singletons and static members).
Sealed class for restricted type hierarchies.

3. Functional programming and collections (1–2 weeks)

Kotlin combines OOP and the functional approach. Master:

Higher-order functions: map, filter, reduce, flatMap.
Extension functions — add methods to any class.
Lambdas, anonymous functions, inline functions.
Working with collections: List, Set, Map and their mutable versions (MutableList).

4. Coroutines and asynchrony (2 weeks)

Coroutines are Kotlin's main feature for parallel tasks. Study:

suspend functions, launch, async/await.
Dispatchers (IO, Default, Main).
Job and Deferred, exception handling in coroutineScope.
Flow — reactive data streams (alternative to RxJava).

5. First project (2–4 weeks)

Apply your knowledge in practice. Choose one of the options:

Console application: a website parser using Ktor Client, saving to a file.
Android application: a simple weather app (Retrofit + Coroutines + Jetpack Compose).
Backend: REST API on Ktor with the Exposed database.

Publish the project on GitHub — this will become the first item in your portfolio.