Learn Kotlin —
Beginner to Professional

No prior experience required. You will write and run your first Kotlin program in module 1 and understand Kotlin's core null safety model by module 2.

1. 01Introduction to Kotlin
   • History of Kotlin — JetBrains, open-source, Google's official Android language
   • Kotlin 2.0: K2 compiler, performance improvements, new features
   • Kotlin vs Java — conciseness, null safety, coroutines, interoperability
   • Setting up: IntelliJ IDEA Community Edition and Android Studio
   • Running Kotlin: REPL, command line, IDE, Kotlin Playground online
   • Your first Kotlin program: main(), print, println
2. 02Basic Syntax and Data Types
   • val (immutable) vs var (mutable) — Kotlin's key variable distinction
   • Basic types: Int, Long, Double, Float, Boolean, Char, String
   • Any, Unit (like void), Nothing (for unreachable code)
   • Type inference: Kotlin deduces types automatically
   • Nullable types: String vs String? — null safety at compile time
   • String templates: "Hello $name" and "${user.firstName}"
3. 03Operators and Expressions
   • Arithmetic, relational, logical, assignment operators
   • Safe call operator (?.) — access nullable values without crashing
   • Elvis operator (?:) — provide default when null
   • Non-null assertion (!!) — when you are certain a value is non-null
   • Operator overloading in Kotlin (plus, minus, times, compareTo)
   • Bitwise and infix operators
4. 04Control Flow Statements
   • if as an expression — returns a value in Kotlin
   • when expression — Kotlin's powerful replacement for switch/case
   • when with sealed classes for exhaustive handling
   • for loops with ranges: for (i in 1..10), downTo, step, until
   • while and do-while loops, break, continue, and labeled jumps
   • Smart casts: after null/type checks, Kotlin auto-casts the variable
5. 05Functions
   • Function syntax: fun name(params): ReturnType
   • Default parameters and named arguments
   • Single-expression functions: fun double(x: Int) = x * 2
   • vararg parameters and spread operator (*)
   • Local functions — functions inside functions
   • Infix functions: "hello" repeat 3 syntax

Collections, OOP, data classes, and sealed classes — the Kotlin features used in every real project, from Android apps to backend APIs.

6. 06Collections and Arrays
   • Immutable vs mutable collections: listOf() vs mutableListOf()
   • List, MutableList, Set, MutableSet, Map, MutableMap
   • Array and IntArray — when to use arrays vs lists
   • Collection operations: filter, map, reduce, fold, any, all, none
   • Advanced: groupBy, flatMap, zip, sortedBy, associateBy
   • Sequences: lazy evaluation for large collection processing
7. 07Classes and Objects
   • Primary constructor and init block
   • Secondary constructors
   • Properties: backing fields, custom getters and setters
   • Visibility modifiers: public, private, protected, internal
   • Object declarations (Singletons) and companion objects
   • Object expressions (anonymous objects)
8. 08Inheritance and Polymorphism
   • open keyword — Kotlin classes are final by default
   • Extending classes and overriding methods and properties
   • Abstract classes: abstract methods and properties
   • Interfaces: default implementations, multiple interface implementation
   • Smart casts with is checks and as/as? casting
   • Delegation pattern with the by keyword
9. 09Data Classes and Sealed Classes
   • Data classes: auto-generated equals(), hashCode(), toString(), copy()
   • Destructuring data classes: val (name, email) = user
   • copy() function for immutable updates
   • Sealed classes — closed hierarchies for exhaustive when expressions
   • Sealed interfaces — more flexible sealed hierarchies in Kotlin 1.5+
   • Enum classes — typed constant sets with properties and methods
10. 10Null Safety and Exceptions
    • Kotlin's type system: nullable (T?) vs non-nullable (T)
    • Safe calls, elvis operator, and non-null assertion in depth
    • let { } for null-safe code blocks
    • Platform types: dealing with Java nullability in Kotlin
    • try/catch/finally and try as an expression
    • Kotlin's checked vs unchecked exceptions — no checked exceptions

Coroutines, Flow, lambdas, and extension functions — the Kotlin features that make it one of the most expressive and productive programming languages in 2026.

11. 11Higher-Order Functions and Lambdas
    • Function types: (Int, Int) -> String
    • Lambdas: syntax, implicit it parameter, multi-line lambdas
    • Trailing lambda syntax — how Kotlin DSLs work
    • Higher-order functions: passing and returning functions
    • Inline functions: why they exist and when to use them
    • Function references: ::functionName, ::ClassName::method
12. 12Extension Functions and Scope Functions
    • Extension functions: adding methods to any class
    • Extension properties: adding computed properties to existing classes
    • Scope functions — the Kotlin developer's most-used tools:
    • let { } — null safety + transform, run { } — compute a value
    • with(obj) { } — group operations, apply { } — configure objects
    • also { } — side effects, and choosing the right scope function
13. 13Kotlin Coroutines
    • What are coroutines? Lightweight threads, structured concurrency
    • suspend functions — functions that can be paused and resumed
    • CoroutineScope, GlobalScope, and structured concurrency
    • launch { } for fire-and-forget, async { } for Deferred results
    • Coroutine dispatchers: Dispatchers.Main, IO, Default, Unconfined
    • Coroutine cancellation, timeouts (withTimeout), and exception handling
14. 14Kotlin Flow
    • What is Flow? Cold streams vs hot streams
    • Flow builders: flow { emit() }, flowOf(), asFlow()
    • Flow operators: map, filter, transform, onEach, debounce, combine, zip
    • Collecting Flow with collect { } and terminal operators
    • StateFlow: hot observable state holder — used in Android ViewModel
    • SharedFlow: event broadcasting to multiple collectors
15. 15Generics
    • Type parameters: class Box<T>, fun <T> identity(value: T): T
    • Variance: out (covariant producer), in (contravariant consumer)
    • Upper bounds: <T : Comparable<T>>
    • Star projection: List<*> when type is unknown
    • Reified type parameters with inline functions — access T at runtime
    • Generic constraints and where clauses

DSLs, Multiplatform, Android, Ktor backend, and testing — the full Kotlin ecosystem used by professional developers at JetBrains, Google, Netflix, and beyond.

16. 16Kotlin Standard Library and DSLs
    • Kotlin Standard Library overview: string, collection, math, IO utilities
    • Lambdas with receivers: building type-safe builders
    • Internal DSLs: Kotlin HTML DSL, Gradle Kotlin DSL examples
    • @DslMarker annotation to prevent receiver leakage
    • Building a custom DSL from scratch
17. 17Kotlin Multiplatform (KMP)
    • What is KMP? Share code across Android, iOS, Web, Desktop, Server
    • KMP project structure: commonMain, androidMain, iosMain
    • expect/actual mechanism for platform-specific implementations
    • Kotlin Multiplatform Mobile (KMM) for Android + iOS
    • KMP stable (2024+): real-world production usage at Netflix, VMware
    • Kotlin/WASM — targeting WebAssembly from Kotlin
18. 18Android Development with Kotlin
    • Kotlin-first Android development — Google's official recommendation
    • Android Activities, Fragments, and lifecycle
    • Jetpack Compose basics: composable functions, state, recomposition
    • ViewModel with StateFlow for reactive UI state management
    • Coroutines on Android: viewModelScope, lifecycleScope
    • Jetpack libraries: Navigation, Room, Hilt DI — Kotlin overview
19. 19Testing in Kotlin
    • JUnit5 with Kotlin: @Test, assertions, lifecycle annotations
    • Kotest: Kotlin-native testing framework with rich DSL
    • MockK: Kotlin-first mocking library — every { }, verify { }
    • Testing coroutines with TestCoroutineScope and runTest
    • Testing Flow with Turbine library
20. 20Best Practices and Coding Conventions
    • Official Kotlin coding conventions from JetBrains
    • Idiomatic Kotlin: prefer val, use data classes, avoid !! operator
    • Common anti-patterns to avoid
    • Ktlint and Detekt for code quality and static analysis
    • Code review checklist for Kotlin projects

Backend with Ktor, Kotlin/Native for native binaries, and Gradle Kotlin DSL for build configuration — specialized paths for specific career directions.

21. 21Kotlin Backend Development with Ktor
    • What is Ktor? JetBrains' asynchronous Kotlin web framework
    • Setting up a Ktor project and defining routes
    • Plugins: ContentNegotiation (JSON), Authentication, Logging
    • Kotlinx.serialization for JSON serialization/deserialization
    • JWT authentication and building a REST API with Ktor
    • Kotlin with Spring Boot — overview of alternative backend path
22. 22Kotlin/Native
    • What is Kotlin/Native? Compiling Kotlin to native binaries without JVM
    • Supported targets: Linux, macOS, Windows, iOS, tvOS, watchOS
    • C interoperability: calling C libraries from Kotlin/Native
    • Memory model in Kotlin/Native (new memory model in Kotlin 1.7.20+)
23. 23Kotlin Scripting and Build Tools
    • Gradle Kotlin DSL: build.gradle.kts vs build.gradle (Groovy)
    • Kotlin Scripting: writing .kts scripts for automation
    • KSP (Kotlin Symbol Processing) — compile-time code generation
    • Version catalogs and dependency management in Kotlin projects