The OpenTelemetry Android Agent was initially built when Java was the predominant language for Android development. Over the years, the platform has shifted towards being one that is primarily Kotlin, so this project will follow suit. This means that we consider the primary use case of this project to be apps written in Kotlin by folks who are familiar with Android development in Kotlin.
In practice, we want our API and code to be structured with the Kotlin language and idioms in mind. This will allow the project to feel more native and be more readable to modern Android developers, thereby reduce one layer of friction of adopting OpenTelemetry: the Java-ness of it all.
Both the public API of the Agent and internal code will be progressively converted into Kotlin. It is a goal for us for all production code to one day be written exclusively in Kotlin.
The OpenTelemetry Android Agent is currently built on the OTel Java SDK and ecosystem. It also exports the OTel Java API for recording OTel signals. This will be the case until official Kotlin versions are released and stabilized under the OpenTelemetry org, which is currently under development.
Java and Kotlin are interoperable from a language standpoint, so in theory, the Agent API is callable from Java. But from a public API standpoint, we consider the Java use case to be unsupported, meaning that as the API evolves, we will NOT make special efforts to preserve Java language consistency or ergonomics. We will only consider an API change "breaking" if it affects the Kotlin use case.
Bugs should not be filed for compatibility issues when calling the Agent API from Java. As such, we advise that all usage are done in Kotlin if possible to prevent syntactic changes from breaking your app's build.