[voidfunc]

Being forced to use anonymous classes to simulate lambdas prior to 8 was the biggest source of annoying boiler plate IMO and was genuinely a bad experience in sufficiently complex or large code bases.

Everything beyond 8 has been nice to have but 8 was the big one.

[kelnos]

Agree, for the most part, but I think records and pattern matching are essential. I started using Scala (2.x) in 2014 or so, and case classes and pattern matching completely blew my mind. if/else trees and switch statements felt so archaic, limited, and verbose after that. I used to joke that Java would eventually adopt enough of Scala to be a pleasant language to work in, and I don't think I was that far off.

(I'll ignore Kotlin... I don't get why people like it.)

[DmitryOlshansky]

I too adopted Scala in 2014 and was really satisfied with FP side and how it all was tied with JVM. Honestly I always felt that JVM is a nice platform with a horribly verbose “assembly” language that is Java.

Fast forward to around 2020 and I had to organize a team to build search engine in JVM. Given how hard it is to find decent Scala developer I surrendered and did this project in Kotlin. Java devs easily pick up and write sensibly FP-style even code, and builtin coroutines are cool. Even though I had to open up the internals of coroutines to get tracing to work they felt a very welcome change compared to say monadic explicit async.

So for me Kotlin is kind of watered down Scala for typical Java folks and I could tolerate it compared to perspective of writing plain Java.