Kotlin for Android: Why It Became the Standard

In short: Kotlin has been Google's preferred language for Android since 2019, and modern tools such as Jetpack Compose are built for Kotlin only. The language is more concise and safer than Java, mainly thanks to built-in null safety and coroutines for asynchronous code, while remaining fully interoperable with existing Java. If you build a native Android app today, you write it in Kotlin. The open question is whether a native app or a cross-platform approach fits your project better.

How Kotlin became the Android standard

Kotlin comes from JetBrains, the company behind IntelliJ IDEA, which Android Studio is based on. The first stable release appeared in 2016. At Google I/O 2017 Google announced official Android support, and in 2019 it declared Android "Kotlin-first": new libraries, documentation and samples are written for Kotlin first.

The switch had a cause. Android developers were stuck for a long time on an older Java version, because the platform supported newer language features only with a delay. Kotlin brought modern concepts to the existing Java runtime without forcing anyone to rewrite code. Both languages can live in one project, so teams could migrate file by file.

What Kotlin does better in app development

Null safety

One of the most common crash causes in Java apps is the NullPointerException: code accesses an object that does not exist. Kotlin's type system distinguishes values that may be empty from values that may not. The compiler forces developers to handle the empty case before the app even builds, which makes this whole class of bugs much rarer.

Less code for the same job

Data classes, type inference, extension functions and compact lambda syntax express the same logic in fewer lines. Less code does not automatically mean better software, but it is easier to read and review.

Coroutines for asynchronous work

Apps constantly load data from the network, read databases or wait for sensors. Coroutines let you write such flows as if they ran in sequence, while the interface stays responsive. That is clearer than nested callbacks and reduces typical bugs such as frozen screens.

Jetpack Compose

Compose is Android's modern UI toolkit. Instead of describing layouts in XML, you define the interface in Kotlin as a function of the current state. Compose has been stable since 2021 and works only with Kotlin. That settled the language question for new Android projects.

Kotlin beyond Android

Kotlin also runs on the server, for example with Spring Boot or Ktor. Of particular interest for apps is Kotlin Multiplatform: business logic, networking and data storage are written once in Kotlin and shared between Android and iOS, while the interface can stay native. Kotlin Multiplatform has been considered stable since late 2023. For teams with a strong Android background it is an alternative to React Native or Flutter.

Native Android app or cross-platform?

Kotlin is the right language when you build a native Android app. The real project question is often whether you need two native apps at all.

Native development, Kotlin for Android and Swift for iOS, pays off when the app works closely with hardware (Bluetooth devices, camera pipelines, background services) or needs top performance. It also means two codebases and usually two specializations on the team. For the iOS side, see building your first iOS app with Swift.

For many business apps a cross-platform framework is more economical. React Native and Flutter deliver both platforms from one codebase, and for typical applications most users cannot tell them apart from native apps. Our comparison of React Native vs. Flutter and our take on native vs. cross-platform performance go into detail. Kotlin still shows up in cross-platform projects, wherever native Android modules have to be written.

Frequently asked questions (FAQ)

Does an existing Java app need to be rewritten in Kotlin?

No. Java and Kotlin run side by side in the same project. A sensible approach is to write new features in Kotlin and migrate existing code gradually whenever you touch it anyway.

Is Kotlin slower than Java?

Not in any way users notice. Kotlin compiles to the same bytecode and runs on the same Android runtime. Build times can be somewhat longer, which only affects development.

Can I build an iOS app with Kotlin?

With Kotlin Multiplatform you can share an app's logic with iOS. The interface is either built natively in SwiftUI or shared with Compose Multiplatform. For iOS-only projects, Swift remains the obvious choice.

When is a native Kotlin app a better choice than React Native?

When the app relies heavily on Android-specific features, is very compute-intensive or will only ship on Android, for example on rugged devices for warehouses and logistics. For typical business apps on both platforms, cross-platform is usually cheaper.

Conclusion

Kotlin won because it fixed Java's concrete weaknesses on Android without devaluing existing projects. For native Android apps the language choice is settled. Whether to go native or cross-platform is a question worth asking fresh for every project.

If you are planning an Android or iOS app and want to find the right approach, talk to us about mobile app development.