Java gets better with every release and is a pretty decent language today. But Kotlin feels just more consistent with less corner cases. Let me name a few things:

    * No checked exceptions destroying lambda expressions and leading to architecture problems (since exceptions are oft not used like the inventors of checked exceptions assumed).
    * Functions are real first class citizens and don't need artificial interfaces.
    * Named parameters with default arguments are very practical.
    * `name: Type` is a better fit for type inference than `Type name`.
    * Null-safety helps to avoid lots of bugs.
    * The type system with `Any` as a unified root and `Unit` instead of the special case `void` makes programming with generics much easier.
    * Constructors are always lean, not only for data classes (record in Java 14).
    * Most things are expressions, so you can write `val a = if(cond) 1 else 99`.
    * Extension functions and operator functions can be used to write simple to use and elegant APIs.

So at least for me Kotlin is definitive the better Java and I wouldn't start a new project with Java, if I could use Kotlin instead.