Picture this: you're a Java developer, working at a solid IT company, cool project, everything's humming along — and then at the team meeting your CTO says: we're moving the backend to Kotlin.

Most people's first reaction: "What? Why? Java works perfectly fine."

What Is Kotlin and Why Developers Are Adding It to Their Resumes - 1

The second reaction — you open Google and start digging. And you discover you're not the first person to hear this from their CTO. Kotlin has been picking up steam for years, and more and more teams are making exactly that call.

So let's break it down: what is Kotlin, where did it come from, and why learn it when Java already works? No evangelism, no "Java is dead!" screaming. It isn't. It's doing just fine.

Who created Kotlin and why

Kotlin was built by JetBrains — the company behind IntelliJ IDEA. The very IDE where most Java developers spend their working day.

They'd been wrestling with Java themselves for years while building IDEA. Endless boilerplate, NullPointerExceptions in production, twenty lines of code where two would do. Developers are patient people, but even patience has limits.

On top of that, other languages — Scala, Groovy, Swift, C# — had already been offering conveniences Java was missing: null-safety, data classes in one line, extension functions, concise lambdas. All of this existed elsewhere. Just not in Java.

At some point, JetBrains decided: enough suffering. They gathered the best ideas from what others had already built, added their own, and created a language that runs on the same JVM, uses the same libraries, and doesn't force Java developers to start from scratch.

Java university

That's how Kotlin appeared in 2016. And no, the name isn't about cats. It's an island in the Gulf of Finland. Java was named after the island of Java — with coffee. Kotlin was named after Kotlin Island — no coffee, but a solid type system.

Why Google backed Kotlin — and what Oracle has to do with it

In 2017, Google announced Kotlin as the official language for Android.

Officially — because developers asked for it and the language is safer and more convenient. That's true.

But there's a backstory worth knowing.

Starting in 2010, Google was locked in a lawsuit with Oracle over Java API usage in Android. Oracle had acquired Sun Microsystems along with Java and immediately filed suit, claiming Google had used 37 Java APIs without a license. The ask: $8.8 billion. The case went all the way to the US Supreme Court and ended in Google's favor only in 2021.

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Eleven years under the shadow of a billion-dollar lawsuit. For scale: $8.8 billion is roughly 88,000 good senior developers for a year. Or a truly unreasonable amount of coffee.

Kotlin from JetBrains is open-source, carries zero licensing risk, and is fully compatible with the Java ecosystem. Google never officially linked the decision to the lawsuit. But the logic speaks for itself.

One upside of all this: the competition pushed Oracle to develop Java more aggressively. Records, sealed classes, pattern matching in newer versions — partly because they needed to keep pace with Kotlin. In the end, every JVM developer came out ahead.

Java is still the backbone of backend — and that matters

It's easy to get confused here, so let's be direct.

Java isn't going anywhere. Spring, Hibernate, massive codebases across most enterprise companies — all of that works and will keep working for a very long time. In terms of job openings, ecosystem size, and maturity, Java is still the industry standard.

Kotlin is growing alongside it. More and more teams are writing new services in Kotlin while leaving their existing Java code untouched. According to the JetBrains Developer Survey 2024, Kotlin is in the top 15 most-used languages in the world.

Think of it like a hammer and a power drill. Nobody's declaring war on the hammer. Some jobs are just easier with the drill.

How Kotlin actually differs from Java

Not in theory — let's look at code.

Null-safety. One of Java's biggest headaches is NullPointerException. It gives no warning. It doesn't apologize. It just crashes at runtime — usually in production, and ideally on a Friday evening.

// Java — everything looks fine until it isn't
String name = null;
System.out.println(name.length()); // NPE. Enjoy your weekend.

// Kotlin — won't even compile
val name: String = null        // Compile error
val name: String? = null       // Explicitly nullable — now fine
println(name?.length)          // If null — returns null, doesn't crash
println(name?.length ?: 0)     // If null — returns 0

Kotlin's compiler knows where null can appear and won't let your code ship until you handle it. Like a strict tech lead, minus the endless Slack messages.

Data class. Classic task — a data model with three fields.

// Java: constructor, getters, equals, hashCode, toString
// Total: roughly half a page of code nobody actually reads
public class User {
    private String name;
    private int age;
    ...
}

// Kotlin — one line
data class User(val name: String, val age: Int)

Kotlin generates everything else automatically, including copy() — a method for creating a copy with modified fields. Java doesn't have that out of the box. Why not — great question.

Extension functions. Add a method to any class without inheritance:

fun String.isPalindrome() = this == this.reversed()
println("racecar".isPalindrome()) // true

Coroutines. Async code that reads like synchronous code. No callbacks, no tangled CompletableFuture chains, no tears.

suspend fun loadData(id: Int) {
    val user = fetchUser(id)       // Waits without blocking the thread
    val orders = fetchOrders(user)
    display(user, orders)
}

Should you learn Kotlin right now

If you work in Android — there's no question. Kotlin is already the standard there.

If you're a backend Java developer — it depends on where you are and where you want to go. For legacy projects at large enterprises, Kotlin isn't a hard requirement yet. But if you're eyeing product companies, startups, or the international job market, the chances of Kotlin showing up in job requirements grow every single year.

Java webinar

Good news: for a Java developer, the switch takes weeks, not months. Same JVM, same logic. IntelliJ IDEA is already installed. All you have to do is start.

You know that old story — a man's house floods and he prays for help, and God sends a truck, then a boat, then a helicopter, but he turns them all down waiting for a proper miracle? Don't be that person. This is your sign.

Try it right now

We have a Kotlin course. 62 levels, 1,100+ tasks with auto-verification, 3 real projects for your portfolio. Same game-like mechanics as the Java course: just code, tasks, and instant feedback — no lectures into the void.

The first level is free.

Keep reading

If you want to jump straight into practice or dig deeper into how the languages compare — here are two articles that follow naturally from this one: