Fundamentals 7 min read

What’s Next for Kotlin? Insights from Chief Designer on Java Interop, Multiplatform, and Loom

Chief designer Michail Zarečenskij explains Kotlin’s evolution from a Java alternative to a multiplatform language, its ongoing reliance on JVM interoperability, hopes for Project Valhalla, the impact of Project Loom on coroutines, and upcoming features slated for the next Kotlin release.

21CTO

Nov 22, 2024

What’s Next for Kotlin? Insights from Chief Designer on Java Interop, Multiplatform, and Loom

Kotlin, created by JetBrains and released in 2011 under the Apache 2.0 license, started as a Java‑compatible alternative for the JVM and has since expanded to JavaScript, native executables, and web packages.

Chief designer Michail Zarečenskij discusses Kotlin’s relationship with Java and its future direction.

"Kotlin was introduced to address Java’s limitations such as null‑safety, checked exceptions, and immutable arrays," he says.

Over the years Kotlin has grown into a multiplatform ecosystem, supporting iOS, Android, Kotlin Notebook, Compose UI, and Gradle scripts written in Kotlin (build.gradle.kts). Nevertheless, the JVM and Java remain crucial, and Kotlin continues to prioritize interoperability because Java will be around for many years.

He notes that Kotlin sometimes waits for Java or JVM features to be implemented. "If Java releases the Valhalla project soon, it will benefit all JVM users," he adds.

Valhalla will bring value types to the JVM, which aligns well with Kotlin. It could enable operator overloading, allowing developers to write "+" instead of ".plus" and other standard symbols, enhancing Kotlin’s expressiveness.

Regarding collaboration with the Java language committee, Zarečenskij explains that it depends on the features. The Kotlin team communicates closely and monitors JVM developments such as value classes to ensure optimal optimization.

Java’s recent introduction of virtual threads via Project Loom raises questions about its impact on Kotlin coroutines. Zarečenskij explains that Loom continues to use the Thread API, while Kotlin relies on structured concurrency with coroutines, which offers finer‑grained control and easier error handling. He hopes that Kotlin coroutines will eventually run on Project Loom’s virtual threads, combining the best of both worlds.

Google’s adoption of Kotlin as the primary language for Android development has driven its growth, but about 40‑45% of Kotlin users now write server‑side applications, and the multiplatform story continues to evolve.

JetBrains does not provide an official Language Server Protocol (LSP) implementation for Kotlin. Non‑JetBrains IDEs like VS Code rely on community projects. Zarečenskij sees LSP becoming essential and hopes for a Kotlin‑specific LSP that leverages the new K2 compiler API, though interoperability challenges remain.

K2, the recently released next‑generation Kotlin compiler, is central to future language improvements.

Kotlin’s next steps

"Key features are immutability and a new error model," Zarečenskij says, adding that the upcoming release will introduce many new language features as work on K2 progresses.

More details will be revealed at KotlinConf 2025 in Copenhagen.