Chapters

60+

Java↔Kotlin examples

100%

Free, no sign-up

2026

Updated for Kotlin 2.2

JAVA KOTLIN Why switch?

Null Safety

Eliminates NullPointerExceptions at compile time

Conciseness

~40% less boilerplate code than Java

100% Java Interop

Call any Java library directly from Kotlin

Coroutines

Async without Thread hell or callback pyramids

Google's First Choice

Official language for Android since 2019

Extension Functions

Add methods to classes you don't own

Your progress 0 of 12 chapters completed

Course Chapters

Introduction

10 min

What is Kotlin, why switch from Java, Hello World side-by-side comparison.

Basic Syntax

12 min

No semicolons, main function, packages, imports and comments.

Variables & Types

15 min

val vs var, type inference, String templates, type casting.

Null Safety ⭐

18 min

Nullable types, ?., ?:, !! — eliminate NullPointerExceptions for good.

Functions

14 min

Default params, named args, single-expression functions, local functions.

Classes & Objects

20 min

Primary constructors, properties, inheritance, companion object vs static.

Data Classes

12 min

Replace Java POJOs. Auto-generated equals, hashCode, copy, destructuring.

Collections

16 min

Immutable vs mutable, Java Streams → Kotlin filter/map/groupBy.

Lambdas & Higher-Order

18 min

Scope functions: run, let, apply, also, with — and function types.

Coroutines ⭐

22 min

Threads vs coroutines, suspend, launch, async, Dispatchers.

Extension Functions

12 min

Add methods to any class — even Java classes you don't own.

Sealed Classes & when

14 min

when expression vs Java switch, sealed classes for state modeling.

Companion Resources

Supercharge your Kotlin learning with these developer tools:

HEX → Compose Color DP ↔ PX Converter Material 3 Canvas ADB Commands

Begin Chapter 1 →