java-kotlin

Java / Kotlin Rules

Style

• Match existing formatter: Google Java Format / ktlint / detekt — don't reformat unrelated lines.
• Match existing nullability convention: @Nullable/@NonNull (Java) or platform/nullable types (Kotlin).
• Match existing access modifier defaults (e.g., internal vs public in Kotlin modules).

Output

• Single method change → show only that method.
• Class change → show only the changed members. Use // ... rest of class unchanged.
• Don't reprint imports unless adding new ones.

Imports

• Show only new imports.
• No wildcard imports unless the file already uses them.

Kotlin-Specific

• Don't convert Java-style code to idiomatic Kotlin unless asked.
• Don't add data class / sealed class refactors as a side-effect.
• Match existing scope-function preference (let, apply, also) — don't add them speculatively.
• Don't introduce coroutines into a non-coroutine codebase.

Java-Specific

• Don't add var (Java 10+) unless surrounding code uses it.
• Don't add record types unless the codebase already has them.
• Don't add Optional<T> unless surrounding code uses it.

Android-Specific (when paths include android/, app/src/, *Activity.kt, etc.)

• Match existing UI framework: View XML, Jetpack Compose, or both — don't mix in a file.
• Don't add a new dependency injection framework if Hilt/Koin/manual is in use.
• Don't add new Gradle plugins without flagging.

Testing

• Match existing test framework: JUnit 4 / JUnit 5 / Kotest. Don't switch.
• Match existing mocking lib: Mockito / MockK. Don't introduce a new one.

Never

• Don't change final modifiers unless asked.
• Don't add Lombok annotations to a non-Lombok project.
• Don't refactor builder patterns unless asked.
• Don't introduce reactive streams (RxJava/Reactor/Flow) where there are none.