Hayden

If you’ve been following Android development or backend trends lately, you’ve probably heard the name Kotlin quite a bit. “What makes Kotlin so special?” If you’re wondering about that, this guide is for you.

When I first encountered Kotlin, I thought Java was sufficient. But once I tried it, the experience was surprisingly different. The code became much more concise, and dealing with NullPointerExceptions became significantly less frustrating.

 

Kotlin

 

 

1. What is Kotlin?

Kotlin is a programming language developed by JetBrains in 2011. JetBrains is the company behind IntelliJ IDEA, one of the most popular IDEs, and they created Kotlin to help developers code more efficiently.

The language gained significant attention when Google announced it as an official Android development language at Google I/O 2017. As of October 2025, the latest stable version is 2.2.20, with 2.3.0-Beta1 also available.

Core Features of Kotlin

100% Java Interoperability: Kotlin code and Java code can coexist in the same project, and you can use existing Java libraries without any modifications. Since Kotlin compiles to the same JVM bytecode as Java, interoperability is seamless.

Concise Syntax for High Productivity: You can achieve the same functionality with 2-3 lines of Kotlin that would take 10-20 lines in Java. Boilerplate code is dramatically reduced.

Built-in Null Safety: Kotlin prevents NullPointerExceptions at compile time. By explicitly distinguishing nullable from non-nullable types in variable declarations, runtime errors are significantly reduced.

 

 

2. How Did Kotlin Come to Be?

The JetBrains team originally used Scala. While Scala is excellent, it had some issues: compilation times were long, and the language’s implicit features created a steep learning curve.

So JetBrains decided to create a language that developers could use immediately in production—one that was “concise yet powerful.” They took Scala’s strengths but removed complexity in favor of explicitness.

Version 1.0 was officially released in February 2016, and after Google’s endorsement in 2017, adoption grew rapidly. In 2018, Kakao reported that applying Kotlin to their KakaoTalk messaging servers dramatically reduced code volume and significantly improved productivity.

 

 

3. How Does Kotlin Differ from Java?

The differences become clear when you compare actual code.

Data Class Comparison

Java Code:

public class User {
    private String name;
    private int age;
    
    public User(String name, int age) {
        this.name = name;
        this.age = age;
    }
    
    public String getName() {
        return name;
    }
    
    public int getAge() {
        return age;
    }
}

Kotlin Code:

data class User(val name: String, val age: Int)

The same functionality in just one line! Using data class automatically generates methods like toString(), equals(), and hashCode().

Null Safety Comparison

Java Code:

String name = null;
int length = name.length();  // Throws NullPointerException!

Kotlin Code:

var name: String? = null  // ? allows null values
println(name?.length)  // Safe call operator handles null safely

In Kotlin, you must add ? to allow null values. The ?. operator (Safe Call) handles null cases gracefully.

Variable Declaration Comparison

Java Code:

int count = 10;
String message = "Hello";

Kotlin Code:

val count = 10  // Immutable variable (val)
var message = "Hello"  // Mutable variable (var)

Kotlin supports type inference, so explicit type declarations are optional. By distinguishing between val (immutable) and var (mutable), code becomes safer.

 

 

4. Powerful Kotlin Features

Coroutines for Asynchronous Processing

One of Kotlin’s most powerful features is coroutines. You can write asynchronous code as concisely as synchronous code.

Java Asynchronous Code:

ExecutorService executor = Executors.newSingleThreadExecutor();
executor.submit(() -> {
    try {
        Thread.sleep(1000);
        System.out.println("World!");
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
});
System.out.println("Hello");

Kotlin Coroutines:

import kotlinx.coroutines.*

fun main() = runBlocking {
    launch {
        delay(1000L)
        println("World!")
    }
    println("Hello")
}

Coroutines handle asynchronous operations intuitively without complex thread management.

Extension Functions

You can add new functionality to existing classes without modifying them.

fun String.addPrefix(prefix: String): String = "$prefix$this"

println("World".addPrefix("Hello "))  // Output: Hello World

This lets you use the new method as if it were part of the original String class.

Smart Casts

fun printLength(obj: Any) {
    if (obj is String) {
        println(obj.length)  // Automatically cast to String!
    }
}

After type checking, Kotlin automatically casts to the appropriate type without explicit casting.

 

 

5. Where is Kotlin Used?

Android App Development

As Google’s official language, Kotlin is most widely used in Android development. It comes built into Android Studio and integrates perfectly with Jetpack Compose.

Real-World Usage:

  • Kakao: Applied Kotlin to KakaoTalk messaging servers, drastically reducing code and improving productivity
  • Forbes: Shares over 80% of business logic between iOS and Android for simultaneous releases
  • McDonald’s: Uses Kotlin Multiplatform for their global mobile app
  • Philips: Implemented in HealthSuite platform SDK, enhancing collaboration between Android and iOS developers

Server-Side Development (Backend)

Kotlin integrates seamlessly with Spring Framework, and the asynchronous framework Ktor is also gaining popularity. Coroutine-based asynchronous processing delivers high performance.

Real-World Usage:

  • AWS: Chose Kotlin over Java for Amazon Quantum Ledger Database (QLDB)
  • Adobe: Migrated Experience Platform real-time services from Java to Kotlin for improved productivity

Multiplatform Development

Kotlin Multiplatform lets you share business logic across iOS, Android, and web platforms. While UI is written platform-specifically, core logic is written once, significantly reducing development time and maintenance costs.

Real-World Usage:

  • Philips: Applied to HealthSuite digital platform mobile SDK
  • Forbes: Shares over 80% of business logic between iOS and Android
  • McDonald’s: Eliminated code duplication in global app

 

 

6. Getting Started with Kotlin: Development Environment Setup

Install IntelliJ IDEA or Android Studio

Kotlin comes bundled with IntelliJ IDEA and Android Studio.

Download Links:

IntelliJ IDEA offers both Community Edition (free) and Ultimate Edition (paid). The Community Edition is sufficient for Kotlin development.

Writing Your First Kotlin Program

  1. Launch IntelliJ IDEA and select New Project
  2. Select Kotlin > JVM | IDEA
  3. Enter a project name and click Create
  4. Create a new Kotlin file in the src folder (File > New > Kotlin Class/File)
  5. Write the following code:
fun main() {
    println("Hello, Kotlin!")
    
    val name = "Developer"
    println("Hello, $name!")
    
    // Loop example
    for (i in 1..5) {
        println("Number: $i")
    }
}
  1. To run, click the green run button to the left of the code or press Shift + F10

Start Online Immediately

If installing a development environment seems daunting, try Kotlin Playground.

Access Here: Kotlin Playground Official Site

You can write and run Kotlin code directly in your browser. It’s perfect for simple learning or testing and includes code-sharing features.

 

 

7. Learning Kotlin: Recommended Resources

Official Documentation

Free Courses

Kotlin Community

 

 

8. Kotlin’s Strengths and Limitations

Strengths

Concise Code: Achieve the same functionality with far less code than Java. Productivity improves significantly.

Null Safety: Prevents NullPointerExceptions at compile time, enhancing stability.

Perfect Java Compatibility: Use existing Java code and libraries as-is, enabling gradual migration.

Modern Language Features: Productivity-boosting features like coroutines, extension functions, data classes, and smart casts.

Multiplatform Support: Kotlin Multiplatform covers Android, iOS, web, and backend.

Limitations

Compilation Speed: Compilation can be slightly slower than Java. The difference may be noticeable in large projects.

App Size Increase: Including the Kotlin runtime library slightly increases APK size.

Learning Curve: Java developers need to learn new concepts like coroutines and extension functions. However, basic syntax is actually simpler than Java.

Smaller Community Than Java: The community is smaller than Java’s, though it’s growing rapidly with strong support from JetBrains and Google.

 

 

9. Kotlin vs Java: Which Should You Choose?

Choose Kotlin When:

  • Starting a new Android project
  • Prioritizing code conciseness and productivity
  • Wanting to leverage modern language features
  • Null safety is critical for the project

Choose Java When:

  • Existing Java project is large and migration costs are high
  • Large team is already proficient in Java
  • Heavy reliance on Java-specific legacy libraries

However, in most cases, you can use Kotlin and Java together. Writing new code in Kotlin while maintaining existing Java code and gradually migrating is a practical approach.

 

 

10. The Future of Kotlin in 2025, 2026

Kotlin continues to evolve. Looking at the 2025 roadmap:

Kotlin 2.2.20 Key Updates (September 2025):

  • Kotlin/Wasm promoted to Beta (run Kotlin in web browsers)
  • Swift Export support by default (enhanced iOS development)
  • Stabilized cross-platform compilation
  • JavaScript BigInt support for improved Long type handling

Kotlin 2.3.0-Beta1 Key Features:

  • Automatic unused return value checking
  • Enhanced type checking and casting
  • Performance optimization and faster compilation

JetBrains is strengthening Kotlin Multiplatform and integrating with AI development tools. They recently unveiled Koog, a Kotlin-based AI agent framework, expanding Kotlin’s reach into AI.

Kotlin has already become the standard for Android development and is growing rapidly in backend development with Spring Boot. It’s also gaining attention as a multiplatform development powerhouse.

 

 

Kotlin goes beyond being simply an “improved Java”—it’s a powerful tool that meets modern software development requirements. Features like concise syntax, null safety, and coroutines significantly boost developer productivity.

Want to build Android apps? Develop backend servers? Try multiplatform development? Whatever your goal, Kotlin is an excellent choice.

It may feel unfamiliar at first, but if you know Java, you’ll adapt quickly. You might even think, “Why didn’t I try this sooner?”

Start writing simple code right now at the Kotlin Playground Official Site. Taking that first step is what matters most!

 

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