This topic, Java vs. Kotlin, is an endless discussion. But, Java is the most acceptable and recognized programming language with millions of developers making a vibrant and robust community. But, its complex code, primary user graphic interface and lots of other things compelled developers to search and develop new languages like Kotlin.
Though Kotlin is getting popularity and acceptability, still a lot needs to be done to make it fully functional on its own. Java is here for another five to ten years as the new languages are dependent on it. But, indeed, one day, Kotlin with its less complicated code, bug-free applications, compactness is going to win the race among developers.