Meta has been making significant progress in translating their Android codebase from Java to Kotlin to maximize developer productivity and null safety. They share tradeoffs made and challenges faced in automating the transition, including the development of their own conversion tool, the Kotlinator. Leveraging custom pre- and post-conversion steps, they handled compatibility issues and minimized the drawbacks of a mixed codebase. Collaborating with JetBrains improved the translation tool and allowed for more accurate symbol resolution. With a focus on null safety, converting from Java to Kotlin requires careful consideration to avoid introducing new issues. Despite challenges, Meta has made significant progress in their Kotlin adoption effort.
https://engineering.fb.com/2024/12/18/android/translating-java-to-kotlin-at-scale/