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17 August 2022

Celebrating 5 years of Kotlin on Android

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Posted by Márton Braun, Developer Relations Engineer

Five years ago, at the 2017 Google I/O Keynote, we did something we had never done before: we announced official support for a new programming language to build Android apps with: Kotlin. It was great to see how excited the Android developer community was about this announcement.

Since then, JetBrains and Google have been collaborating around the development of Kotlin, and the Kotlin Foundation was co-founded by the two companies.

As highlighted in those initial I/O announcements, Kotlin is interoperable, mature, production-ready, and open source. It also has outstanding IDE support, as JetBrains develops both the language and its tooling.

Now, five years have passed since the original announcement. To celebrate the amazing language that now powers modern Android app development, we’re taking a quick look at the journey of Kotlin on Android. This post includes quotes from a handful of people who were involved in making Kotlin on Android a success, who are joining us for this celebration.

Early years

The Kotlin adoption story started before official support from Google, within the Android developer community. The excitement in the community was one of the main reasons to invest in official support.
“The decision by Google to add support for Kotlin, I think we underestimate how wild of a notion that was at the time. The odds of another company that size making a similar decision based on community support and enthusiasm is very low.“ (Christina Lee, Android engineer at Pinterest, Kotlin and Android GDE)

After the 2017 announcement, Android Studio started shipping with built-in support for Kotlin. Lots of documentation and samples were updated to use Kotlin.

In 2018, we launched the Android KTX libraries, which provide Kotlin-friendly extensions wrapping the APIs of the Android framework and several AndroidX libraries. Tooling improved further, too, with Kotlin-specific live templates, lint checks, and optimizations in R8 and ART. The reference documentation for Android was also published in Kotlin for the first time.

Going Kotlin-first

At Google I/O 2019, we committed to Kotlin-first Android development, further increasing our investments in the language.
“If you look at a Kotlin new users graph, you immediately notice the two most significant spikes – one in May 2017 and another in May 2019. We have an inside joke about it: ‘Marketing a programming language is easy. All you have to do is make the largest operating system in the world call it an official language during the annual keynote’” (Egor Tolstoy, Kotlin Product Lead at JetBrains)

Being Kotlin-first means that we now design our documentation, samples, training content, new libraries and tools for the Kotlin language first, while still supporting users of the Java programming language.

”Now when we want to start a Jetpack Library, we are writing it in Kotlin unless we have a very, very, very good reason not to do that. It’s clear that Kotlin is the first-class language.” (Yigit Boyar, early proponent of Kotlin within Google, currently leading the development of a handful of Jetpack libraries)

Some examples of Kotlin-first Jetpack libraries are Paging 3 and DataStore, which are both powered by coroutines and Flows for asynchronous operations.

Jetpack Compose, Android’s modern UI toolkit is our greatest commitment to Kotlin so far, as it’s Kotlin-only. It’s powered by a Kotlin compiler plugin, and it makes extensive use of advanced language features like coroutines, top-level functions, and trailing lambdas.

“Kotlin is here to stay and Compose is our bet for the future. Right now, for developers that are starting to learn Android, we’re already recommending the Android Basics with Compose course.” (Florina Muntenescu, Jetpack Compose developer relations lead)

Kotlin beyond Android

Even though Kotlin is a great fit for Android, it’s a general-purpose language and not solely for use on Android. For teams within Google, Kotlin is now generally available to use for both Android and server-side projects. Thousands of Google engineers are writing Kotlin code, and our internal codebase contains more than 8.5 million lines of Kotlin code to date. This number has been increasing rapidly as well, doubling year over year.
“We’ve been working to bring Kotlin to Google engineers for the last few years by adding Kotlin support to all the tools they use. This includes the build system, static analysis tools, libraries and APIs. We’ve talked a lot about encouraging developers to use Kotlin for Android app development, and we strongly encourage using Kotlin for server-side development as well.” (Kevin Bierhoff, lead of the Kotlin at Google team, which supports Google engineers writing Kotlin code)

gRPC Kotlin and Kotlin for protocol buffers are examples of Kotlin projects Google uses both in Android apps and on servers that have been open sourced and are now receiving community adoption and contributions. Kotlin is also supported on Google Cloud.

Collaboration with JetBrains

There is close collaboration between JetBrains and Google around the development of Kotlin. The Kotlin Foundation was co-founded by the two companies, and it ensures that the language and ecosystem age well.

Google engineers have also been working on improving the compiler and on creating important tooling for the language.
“My team is helping JetBrains with rewriting the Kotlin compiler right now, and we also work on Kotlin Symbol Processing, which is the first compiler-related Kotlin project that’s been completely done at Google. We work more closely with JetBrains than some other parts of Google." (Jeffrey van Gogh, member of the Kotlin Foundation, lead of the Kotlin engineering team at Google)

JetBrains and Google also coordinate new releases of the language and the accompanying tooling so that developers are able to use the latest releases as smoothly as possible.
“The collaboration gets stronger over time, and I’m really excited to see its impact on Kotlin’s future. Our coordinated pre-release checks are getting better and better." (Liliia Abdulina, Kotlin QA team lead at JetBrains)

Learn more and share your own stories

You can read more stories about Kotlin from our interviewees in the accompanying Medium post. We’d also love to hear your stories of learning and adopting Kotlin for Android development! Share them on social media using the hashtag #Hi5KotlinOnAndroid!

Finally, let’s appreciate these kind words about Kotlin’s accomplishments to conclude our story.

“Technology can really change people's lives and it can really make people happier at work. We normally focus on ‘there's null safety’ or ‘there's type inference’ or all these other technical parts. But when you take a step back, there's a whole story in there about all of the people who had their passion for coding ignited or reignited because Kotlin is such a wonderful language. It's just so impressive that the team is able to do what they're able to do and that the community is as good as it is." (Christina Lee, Android engineer at Pinterest, GDE for Android and Kotlin)

Have a nice Kotlin on Android!

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