Scala presents itself as THE programming language for concurrency and scalability, but I've heard of many cases where Scala was not sufficiently efficient in really big and complex applications and when changed from Scala to Java they achieved a much better performance. Something about Java libraries/frameworks being much more tuned...
Does someone has real world experience that can confirm/deny this?
In general, performance is not the reason I would choose Java over Scala.
And which reasons would make you choose Java over Scala?
Much more troubling:
- Some Scala idioms are just not as performant as the naive java implementations. Function passing can create lots of objects for instance.
- Some of Scala's "magic" features that allow for terse-ness can behind the scenes cause performance issues, that you might not expect without a clear understanding of what is going on. Implicit conversions for instance can also create tons of garbage.
- The Scala collections library, while improving some, has lots of performance gotchas. Collections that don't match modern hardware or implicit conversions that de-optimize operations can happen pretty easily.
Personally, I would choose Java over Scala if any of the following were true:
- You were going to have many different versions of your software in the wild.
- You had a constrained release cycle.
- You intended for artifacts to exist for long periods without change.
- You had specific backwards compatibility requirements.
- You had a large team.
- You had a team of highly varying skill sets.
That is to say, I'd only pick Scala if I were working on a project where I controlled the life cycle of the product, releases were common, backwards compatibility was not an issue, and my team was small, cohesive and experienced.
If those things weren't true, I might not pick Java, but I certainly wouldn't pick Scala.