Kotlin 2025 Learning Plan: Where to Start for Beginners

Kotlin Learning Plan 2025: Where to Start and How Not to Get Lost

Kotlin is one of the fastest-growing programming languages in 2025. It is officially supported by Google for Android development, actively used in backend (Spring Boot), Data Science, and even in multiplatform applications (KMP). If you have decided to start learning Kotlin this year, we have prepared a step-by-step learning plan that will help you master the language from scratch to a confident Junior developer.

Why Kotlin in 2025?

Kotlin combines the conciseness of Python and the power of Java. It is safe (null-safety), compatible with the Java ecosystem, and allows you to write code 2–3 times faster. The job market for Kotlin developers has grown by 40% over the past year, and the average salary for a Junior specialist is 120–180 thousand rubles.

Stage 1: Syntax Basics (2–3 weeks)

• Variables and Data Types: val vs var, String, Int, Boolean, Any
• Conditional Statements: if, when (replacement for switch)
• Loops: for, while, range
• Functions: declaration, default parameters, lambdas
• Null safety: ?., ?:, !! — a mandatory topic for Kotlin

Resources: official Playground (play.kotlinlang.org), the book "Kotlin in Action" or an interactive course on JetBrains Academy.

Stage 2: Object-Oriented Programming (3–4 weeks)

• Classes, constructors, properties (get/set)
• Inheritance, interfaces, abstract classes
• Data class and object (singleton)
• Sealed class and enum
• Generics: in/out, where

Practice: write a simple console application (e.g., a calculator or task manager).

Stage 3: Functional Programming and Collections (2 weeks)

• Higher-order functions: map, filter, reduce, flatMap
• Sequence vs List — lazy evaluation
• Scope functions: let, apply, run, with, also
• Extensions (extension functions)

This stage is Kotlin's "superpower." Mastering it will allow you to write code in the style of Python, but with Java's typing.

Stage 4: Advanced Topics (3–4 weeks)

• Coroutines and asynchrony — the foundation of modern Kotlin
• Flow for reactive streams
• Kotlin Serialization and working with JSON
• Testing: JUnit5, MockK, Spek

Project: create a simple REST API using Ktor or Spring Boot with two endpoints.

Stage 5: Specialization (choose a direction)

• Android: Jetpack Compose, Room, Retrofit, Navigation
• Backend: Spring Boot, Ktor, Exposed (ORM), Koin
• Multiplatform (KMP): Shared module for iOS/Android

For each direction, there are ready-made roadmaps on the website pythonlib.ru — we regularly update them for