scala vs java, performance and memory? [closed]

Answer 1

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" :)

Answer 2

I'm a new user, so I'm not able to add a comment to Rex Kerr's answer above (allowing new users to "answer" but not "comment" is a very odd rule btw).

I signed up simply to respond to the "phew, Java is so verbose and such hard work" insinuation of Rex's popular answer above. While you can of course write more concise Scala code, the Java example given is clearly bloated. Most Java developers would code something like this:

List<String> bigEnough = new ArrayList<String>();
for(String s : array) {
  if(s.length() > 2 && mapping.get(s) != null) {
    bigEnough.add(mapping.get(s));
  }
}

And of course, if we are going to pretend that Eclipse doesn't do most of the actual typing for you and that every character saved really makes you a better programmer, then you could code this:

List b=new ArrayList();
for(String s:array)
  if(s.length()>2 && mapping.get(s) != null) b.add(mapping.get(s));

Now not only did I save the time it took me to type full variable names and curly braces (freeing me to spend 5 more seconds to think deep algorithmic thoughts), but I can also enter my code in obfuscation contests and potentially earn extra cash for the holidays.