为什么新的 Android 功能（Proto DataStore）仍然生成 Java 代码而不是 Kotlin？

Question

I'm investigation

implementation  "androidx.datastore:datastore-core:1.0.0-alpha01"
implementation  "com.google.protobuf:protobuf-javalite:3.10.0"

via this codelab

I do not understand why the associated DataStore generated classes are Java

I thought Google announced that Kotlin had replaced Java as the primary Android development language?

I was under the impression Kotlin had many advantages over Java

is the issue proto buffers do not support Kotlin?

Answer 1

I can answer that quickly!

According to codelab link you shared, If you visit page 6 first line indicates something where your answer relies:

Protocol buffers are a mechanism for serializing structured data. You define how you want your data to be structured once and then the compiler generates source code to easily write and read the structured data.

So, basically under the hood, library is using code generator plugin that generates classes required for protobuf to work with project. (Yes, you can relate same thing with data-binding where you write code on xml and under the hood there's generated class that actually implements that logic for you)

And that's the reason 'generated classes are in Java'. It has nothing to do with source in this context (Java/Kotlin support to library) . Anything written in Java will seamlessly work on Kotlin and vice versa (Considering Android development context)

Side note: You can also relate it to annotation processor where we actually generate Java code based on annotation on any criteria.