For programmer's wanting to get to know Kotlin, here is a side-by-side comparison of Java and Kotlin covering features, variables, functions, classes, collections and more.
As to why you would want to get acquainted with Kotlin, there are several reasons. First unlike Java, it's modern and as such does not carry the burden of the past in trying to stay compatible with it at any cost.
However, Java is still going strong as we've seen in "How is Java Doing?-State of Java in 2019" despite being heralded as the 'old horse' of the programming language collective:
Java has always been the favorite - enterprises talked and still talk Java. Look no further than the Fortune 500 list of companies reliance on it. Yes, Blue Chips love it.
But for young startups, those fresh to the art of programming or on the other side, those experienced but looking for better alternatives or feeling adventurous, Java is unfortunately not recommended.