Chapter 1: Introduction to Kotlin
1. What Exactly is Kotlin? (In very simple human words)
Imagine Java is like an old, very reliable but very talkative uncle who always explains everything in 10 sentences when 2 would be enough.
Kotlin is the same uncle — but now he learned to speak concisely, politely, and safely. He still can do everything the old uncle could do, but he says it in a much nicer, shorter, and safer way.
Officially: Kotlin is a modern, statically-typed, general-purpose programming language developed by JetBrains that:
- Runs on the JVM (same as Java)
- Is 100% interoperable with Java
- Can also be compiled to JavaScript, native binaries (Kotlin/Native), and even WebAssembly
But the real magic is: Kotlin lets you write 50–70% less code than Java while being much safer (especially against null pointer exceptions).
2. A Short but Interesting History of Kotlin
| Year | What happened? | Why it matters to you today |
|---|---|---|
| 2010 | JetBrains starts a secret internal project called “Kotlin” | They wanted to fix Java’s pain points |
| July 2011 | First public announcement at JVM Language Summit | People got curious |
| Feb 15, 2016 | Kotlin 1.0 released — officially production-ready | This is when serious companies started looking |
| May 2017 | Google announces official support for Kotlin for Android at Google I/O | Huge turning point — Android world exploded with Kotlin |
| 2019 | Google declares Kotlin is now the preferred language for Android | Java became “second class” on Android |
| 2021 | Kotlin 1.5 — inline classes, unsigned types, new compiler backend | Performance & modern features improved dramatically |
| 2023–2024 | Kotlin 1.8 / 1.9 / 2.0 — new super-fast K2 compiler, context receivers, huge Multiplatform improvements | Kotlin became truly multiplatform |
| 2025–2026 | Kotlin is now used by Netflix, Airbnb, Pinterest, Square, Trello, Autodesk, Coursera, Atlassian, McDonald’s… | You are learning one of the hottest languages right now! |
Philosophy behind Kotlin (JetBrains’ own words):
“We believe that a programming language should be pleasant to read and write, safe by default, and pragmatic — solving real developer problems without unnecessary complexity.”
That’s exactly what they achieved!
3. Why Choose Kotlin? (Head-to-Head Comparison – 2025/2026 Perspective)
| Feature / Pain Point | Java (classic) | Kotlin (modern) | Scala | Python / TypeScript |
|---|---|---|---|---|
| Null Safety | No — famous NullPointerException hell | Built-in at compile time — game changer! | Has Option but more verbose | No (runtime errors) |
| Code length / Boilerplate | Very high (getters, setters, equals, hashCode…) | Extremely low — data classes do it all | Medium–high | Very low |
| Java library compatibility | — | 100% perfect interop | Good but sometimes painful | Almost none |
| Performance | Excellent | Same as Java | Same as Java | 10–100× slower |
| Learning curve (if you know Java) | — | Very easy — you already know 70% | Steep (functional + complex types) | Easy but different paradigm |
| Modern language features | Slow to adopt (records, sealed classes late) | Lambdas, extensions, coroutines, DSLs, context receivers… | Many (but complex) | Many (dynamic) |
| Android | Still supported but painful | First-class + preferred | Not really | Not possible |
| Multiplatform (Android + iOS + Desktop + Web) | Only JVM | Excellent (Kotlin Multiplatform + Compose) | Limited | Limited |
| Community & Job Market (2025) | Huge but shrinking for new projects | Exploding — especially Android & backend | Niche | Huge (but different domains) |
Real example — same task in Java vs Kotlin:
Java (old style – 20+ lines):
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public class User { private final String name; private final int age; public User(String name, int age) { this.name = name; this.age = age; } public String getName() { return name; } public int getAge() { return age; } @Override public boolean equals(Object o) { ... } @Override public int hashCode() { ... } @Override public String toString() { ... } } |
Kotlin (1 line + nice!):
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data class User(val name: String, val age: Int) |
→ Automatically gets: toString(), equals(), hashCode(), copy(), component1(), component2()…
This is why developers love Kotlin — less typing, fewer bugs, more fun.
4. Real-World Use Cases of Kotlin in 2025–2026
| Domain | Main Tools / Frameworks | Famous Companies / Apps using Kotlin heavily |
|---|---|---|
| Android Mobile | Jetpack Compose, Coroutines, Flow, Hilt, Retrofit, Room | Google, Airbnb, Pinterest, Trello, Evernote, Square, Duolingo, Netflix, Uber |
| Backend / Server | Spring Boot 3, Ktor, Micronaut, Quarkus, Exposed | Netflix, Pinterest, Atlassian, Autodesk, JetBrains, Coursera, Gradle |
| Kotlin Multiplatform (KMP) | Shared logic + Compose Multiplatform (Android + iOS + Desktop + Web) | Netflix (mobile + TV), Autodesk, Cash App, McDonald’s, 9GAG, Philips |
| Desktop Applications | Jetpack Compose for Desktop, TornadoFX | JetBrains internal tools, some financial & scientific apps |
| Scripting & Build Tools | .kts Gradle scripts, Kotlin Script | Almost all modern Gradle-based projects |
| Data Science | Kotlin Dataframe, Kotlin Jupyter Notebook | Growing fast in startups & research teams |
Real story from 2025: Netflix rewrote large parts of their Android and TV apps in Kotlin Multiplatform + Compose Multiplatform — one shared codebase for Android, iOS, and TV!
5. Setting Up Your Environment (Step-by-Step – Very Detailed)
Recommended Way #1: IntelliJ IDEA (Best & Easiest – 95% of Kotlin developers use this)
- Download IntelliJ IDEA Community Edition (completely free forever) → https://www.jetbrains.com/idea/download/ Choose your OS (Windows / macOS / Linux)
- Install JDK 17 or 21 (Long-Term Support – best choice in 2025)
- Easiest way: During project creation, IntelliJ will offer to download it automatically
- Manual way (recommended): → https://adoptium.net/ → Choose Temurin 21 (or 17) → Install
- Create your very first Kotlin project
- Open IntelliJ IDEA
- Click New Project
- Left side: Choose Kotlin
- Right side: Choose JVM | IDEA
- Project name: MyFirstKotlinProject
- JDK: select 21 (or let IntelliJ download it)
- Click Create
- You will see this file:src/main/kotlin/Main.kt
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fun main() { println("Hello, Kotlin!") } |
→ Click the green ▶ Run button next to fun main() — and you’ll see: Hello, Kotlin! in the console. Congratulations — you just ran your first Kotlin program! 🎉
Way #2: Kotlin Playground (Zero Installation – Browser Only)
→ https://play.kotlinlang.org
- Just open it
- Delete everything
- Write:
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fun main() { println("Hello from the future! 🌟") } |
- Click Run
- Instant result — perfect for learning first 15 chapters
Way #3: Command Line (For Terminal Lovers)
- Install JDK 17 or 21
- Install Kotlin compiler:
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# Using SDKMAN! (best for Mac/Linux) curl -s "https://get.sdkman.io" | bash source "$HOME/.sdkman/bin/sdkman-init.sh" sdk install kotlin |
- Create file Hello.kt
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fun main() { println("Hello from terminal!") } |
- Compile & run:
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kotlinc Hello.kt -include-runtime -d Hello.jar java -jar Hello.jar |
Or even simpler (Kotlin script):
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# Create Hello.kts echo 'println("Hello from script!")' > Hello.kts kotlin Hello.kts |
Summary – Why You Should Be Super Excited About Learning Kotlin
- Null safety → almost no more NullPointerException crashes
- Much less code → you write once, not ten times
- Full Java ecosystem → millions of libraries
- Beautiful modern features → coroutines, extensions, DSLs…
- Multiplatform future → Android + iOS + Desktop + Web from one codebase
- Best tooling in the world → IntelliJ IDEA is love ❤️
Your Tiny Homework (5–10 minutes)
- Install IntelliJ IDEA Community + JDK 21 (or use Playground)
- Create a project or open Playground
- Run this little program and smile:
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fun main() { val name = "My Friend" println("Hello, $name! Welcome to the wonderful world of Kotlin! 🚀") } |
When you’re ready and smiling, just reply:
- “Chapter 2 ready!”
- “Let’s do Chapter 2”
- or “Chapters 2 to 4 please” (if you want to go faster)
I’m right here with you — every single step! 😊💙
