How to access Kotlin companion object in Java?

You can add @JvmStatic annotation to the method in companion object to make Kotlin generate a static method.

class MainApplication : Application() {
    companion object {
        @JvmStatic fun get(context: Context): MainApplication {
            return context.applicationContext as MainApplication
        }
    }
}

you can then access it from Java like before converting to Kotlin:

MainApplication application = MainApplication.get(mContext);

EDIT: I feel obliged to add something I learned recently: @JvmStatic doesn’t actually move where the method gets generated. It duplicates it, by generating a static method for Java in addition to the method on the companion object. Personally I think this isn’t great and it can have some implications depending on a use case, so something worth knowing.