Kotlin Tutorials

A structured Kotlin learning repository that starts with the language fundamentals and progresses to modern Kotlin 2.4 patterns used in production. Every lesson is a small, runnable file.

Requirements

• JDK 21 or newer (Gradle can provision a matching toolchain if one is missing)
• No separate Gradle install — use the wrapper in this repo

Stack

Component	Version
Kotlin	2.4.20
Gradle Wrapper	9.7.1
JVM toolchain	21
Coroutines	kotlinx-coroutines-core:1.11.0
Serialization	kotlinx-serialization-json:1.11.0
Tests	kotlin("test") + JUnit 6.1.3

Versions are centralized in gradle/libs.versions.toml.

Run

./gradlew clean build
./gradlew test
./gradlew run --args='list'
./gradlew run --args='run variables'
./gradlew runAllLessons
./gradlew runModern

Task	What it does
run	Lesson index / single-lesson runner (LessonsRunner.kt)
runAllLessons	Every non-interactive foundation lesson in one pass
runModern	Modern track entrypoint (modern2026/Modern2026Runner.kt)

You can also open any lesson file and run its main() from the IDE.

Curriculum

Track	Focus	Key files	Level	Time
Foundations	Variables, types, conversions, operators	Variables.kt, BasicTypes.kt, TypeConversion.kt, ArithmeticOperators.kt, AssignmentOperators.kt	Beginner	4-6 hours
Input & flow	Console I/O and branching	InputOutput.kt, IfExpression.kt, IfElseIfExpression.kt, When.kt	Beginner	3-4 hours
Loops & ranges	Iteration and loop control	ForLoop.kt, WhileLoop.kt, DoWhileLoop.kt, Range.kt, Break.kt, Continue.kt, InOperator.kt	Beginner	4-5 hours
Collections	Arrays and maps	Arrays.kt, MapExample.kt	Beginner	2-3 hours
Functions	Declarations, overloading, recursion, infix, extensions	Functions.kt, MethodOverloading.kt, RecursiveFunction.kt, InfixFunction.kt, ExtensionFunction.kt	Beginner → Intermediate	5-7 hours
Object-oriented Kotlin	Classes, constructors, inheritance, interfaces	ClassObjects.kt, Constructor.kt, Inheritance.kt, InterfaceSample.kt, VisibilityModifiers.kt, AbstractClass.kt	Intermediate	6-8 hours
Data modeling	Data classes, sealed types, companion objects	DataClass.kt, SealedClass.kt, CompanionObject.kt, OperatorOverloading.kt	Intermediate	4-5 hours
Modern Kotlin	Value classes, Result, scope functions, state modeling	modern2026/ValueClassAndTypeSafety2026.kt, modern2026/ResultAndScopeFunctions2026.kt, modern2026/SealedAndDataObject2026.kt	Intermediate → Advanced	4-6 hours
Concurrency	Coroutines, structured concurrency, Flow	modern2026/CoroutinesFlow2026.kt	Advanced	3-4 hours
Serialization	Type-safe JSON encode / decode	modern2026/Serialization2026.kt	Advanced	2-3 hours
Testing	Smoke checks for the modern lessons	src/test/kotlin/modern2026/Modern2026SmokeTest.kt	Intermediate	2-3 hours

Total guided time: about 39-54 hours.

Learning outcomes

After finishing the full path, you should be able to:

• Write clear, idiomatic Kotlin for everyday development
• Model domain states safely with sealed types and value classes
• Build asynchronous pipelines with coroutines and Flow
• Encode and decode typed JSON payloads
• Run and verify a Kotlin project with Gradle and tests

Kotlin 2.4 notes

This repository is aligned with Kotlin 2.4.20 and the official coding style:

• readlnOrNull() instead of the deprecated readLine()
• data object for singleton sealed states
• @JvmInline value class for type-safe wrappers
• Result plus scope functions for fallible work
• tailrec for stack-safe recursion
• Version catalog (gradle/libs.versions.toml) for a single source of truth

References

• Kotlin documentation
• Coroutines overview
• Serialization
• kotlinx.coroutines
• kotlinx.serialization

License

This project is released under the MIT License.

MIT License

Copyright (c) 2026 Halil Ozel

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.