Write your Scala like Java, and you can expect almost identical bytecode to be emitted - with almost identical metrics.
Write it more "idiomatically", with immutable objects and higher order functions, and it'll be a bit slower and a bit larger. The one exception to this rule-of-thumb is when using generic objects in which the type params use the @specialised annotation, this'll create even larger bytecode that can outpace Java's performance by avoiding boxing/unboxing.
Also worth mentioning is the fact that more memory / less speed is an inevitable trade-off when writing code that can be run in parallel. Idiomatic Scala code is far more declarative in nature than typical Java code, and is often a mere 4 characters (.par) away from being fully parallel.
So if
- Scala code takes 1.25x longer than Java code in a single thread
- It can be easily split across 4 cores (now common even in laptops)
- for a parallel run time of (1.24 / 4 =) 0.3125x the original Java
Would you then say that the Scala code is now comparatively 25% slower, or 3x faster?
The correct answer depends on exactly how you define "performance" :)
