By "Java going obsolete soon", I mean to make a point that means if Kotlin is now the official language of Android, then Google will be pushing its weight on Kotlin instead of Java, and slowly Kotlin will be taking over Java generating Kotlin jobs and opportunities. Now, thinking in terms of high demand and low supply, there will be less Kotlin developers and more demand which simply translates into high salary. Also, learning java means you will be required to have 5+ years(just an example) of experience, no one can dare to ask 5+ years in Kotlin. So, with all this into one package, it renders into Kotlin being more useful to learn than Java. If everybody has time to learn java and kotlin both, then that's really great, but it turns out, people don't have time nowdays, they are busy doing cool stuff in their domain.