I have been trying to translate this Kotlin code to Java since the project is in Java. I am translating by looking into Kotlin syntax. However, there are still others that I am having a hard time understanding. https://github.com/airbnb/lottie-android/blob/master/LottieSample/src/main/kotlin/com/airbnb/lottie/samples/AppIntroActivity.kt Specifically: For the setViewPagerScroller, I was able to translate the first part. Answer The method setViewPagerScroller uses kotlin anonymous inner class