Past the syntax similarities, both of these languages are intended replacements for an 'old' language (Objective-C => Swift, Java => Kotlin) on a dominant mobile platform, with interoperability as a major selling point (requirement?). As a mobile dev (mainly iOS) this is awesome to see and although I love me some Objective-C, working with swift has been a pleasure. Now Java on the other hand... (shudders).
With Google making Kotlin an official/first-class language and the syntax being so similar to swift I could see myself spending more time working with Android.
I assume Google will try to replace Java with Dart, because they have recently been focused on Flutter [1] [2] and Fuschia [2] development which are (mostly) C++ and DartLang stack.
> I assume Google will try to replace Java with Dart
I would have expected this, but not after pushing Kotlin. Kotlin is shiny enough to temporarily distract the typical developer from the daily struggles with the abysmal Android API.
Kotlin and Java it will be for the next 10 years, for better or worse.
Dart is not very popular within Google itself, and Fuchsia is nothing more than a paid hobby project[0].
According to what Fuchsia developer Travis Geiselbrecht said in the public Fuchsia IRC channel,the OS “isn’t a toy thing, it’s not a 20% project, it’s not a dumping ground of a dead thing that we don’t care about anymore.”[0]
Given the level of activity on [Fuchsia's project repos][0], I find it very unlikely that it's just a hobby project. That amount of activity is on-par with Android itself. If it is just a hobby, it's an extremely expensive one.
> both of these languages are intended replacements for an 'old' language (Objective-C => Swift, Java => Kotlin)
It may be true for Swift but Google never claimed Kotlin is replacement of Java. I guess people are getting overly excited and making claims that Google did not. Kotlin is low effort developer friendly move by Google. Jetbrains will do work on language and tooling and Google would provide some Android-Kotlin related docs and support.
That's true Google never named Kotlin as a replacement to Java. Although naming it a first-class Android language seems like a pretty big move (actions over words), and given an official option between Java and Kotlin I believe most dev's will begin moving towards Kotlin. intended was probably the wrong word for me to use, should have been probable or likely.
