You do realize there are plenty of languages out there, and most novel features appeared first in some minor research languages? Like, there is hardly anything original to kotlin on your list, sealed classes have been in scala forever, and are basically just algebraic data types. Data classes are.. data classes, multiline strings is a cool but very basic syntactic sugar available in millions of languages, coroutines have been around, and kotlin’s couroutines are nothing like project loom. The latter is more similar to go’s threads. Switch expressions have been in scala forever, but a pretty basic thing in FP languages.

Of course none of this is new, but the lead time from Kotlin adoption to Java adoption of all of them is near identical.

That’s irrelevant. It’s not like the language team didn’t know about these features. The change to the shorter release cycle and increased funding is much more behind the speed up of updates regarding Java.

You keep claiming that the language team's knowledge of a feature drives that feature's adoption.

That's not accurate.

Popularity of a feature and enterprise demand drive it's adoption.

It doesn't really matter what the language team knows, it matters what the average developer knows since their collective wants are in large part what drives the language team.

There are hundreds of thousands of Java devs who only ever wrote Java and suddenly had to write Kotlin, and are now clambering for these feature improvements in Java.

1. That's not really right. You're correct that "readiness" is important, but Python and JS are much bigger forces than Kotlin, and the main reason Java is getting features faster is because the investment in the platform has grown (and Kotlin was created when it was at an ebb). But so far, almost all linguistic features added after 1.0 -- generics, lambdas, type inference, ADTs, patterns -- are inspired by ML.

2. Java addresses those topics (where relevant) pretty much in the opposite way from Kotlin. Java rejected coroutines and is going down a completely different path with virtual threads; Java rejected data classes and chose to go down algebraic data types. So if you think Java gets inspiration from Kotlin, then it is in the form of what not to do.

I would agree with you, Java routinely uses the "last-mover's advantage" tactic, but I think you overestimate the relative sizes of the two languages. These are all very basic FP "features"/language primitives, and Java is steering strongly towards becoming an ML-inspired FP-enhanced language.

If anything, the acceptance of more parts of the FP paradigm into all major languages (like C#, JS/TS, C++) starting with lambdas likely have pushed Java, but to single out the all-around very niche Kotlin language as a source is imo a non sequitur.

There are almost 3 billion Android devices. I think you underestimate the scope of the primary language on one of the world's most prolific OS's.

There aren't as many mobile developers as you'd think: https://www.hiringlab.org/2019/11/19/todays-top-tech-skills/

That article is from 2019 and only focuses on languages. At that time most of the Android jobs would be hopelessly intertwined with the Java jobs.

It's also important to not be US centric. In many parts of the world Android is the dominant OS.

These aren’t ‘Kotlin features’ they’re just normal language features.

I really struggle to see Kotlin as being part of the debate here. These features are being driven by enterprise Java user pain points. And those people aren’t looking at Kotlin.

I agree that this would probably happen in the Java world, regardless of kotlin. However, I disagree with the statement that enterprise Java users are not looking at kotlin. From my view (in a large, global consulting business), we see large enterprise Java users adopting kotlin.

>These features are being driven by enterprise Java user pain points

By Java devs who only ever wrote Java, and suddenly had to write Kotlin for Android. They're now aware of these features as a result and are demanding them in Java.