Hidden performance cost in Scala?

Question

I came across this old question and did the following experiment with scala 2.10.3.

I rewrote the Scala version to use explicit tail recursion:

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Answer 1

I changed the val

private val t = 20

to a constant definition

private final val t = 20

and got a significant performance boost, now it seems that both versions perform almost equally [on my system, see update and comments].

I have not looked into into the bytecode, but if you use val t = 20 you can see using javap that there is a method (and that version is as slow as the one with the private val).

So I assume that even a private val involves calling a method, and that's not directly comparable with a final in Java.

Update

On my system I got these results

Java version : time: 14725

Scala version: time: 13228

Using OpenJDK 1.7 on a 32-Bit Linux.

In my experience Oracle's JDK on a 64-Bit system does actually perform better, so this probably explains that other measurements yield even better results in favour of the Scala version.

As for the Scala version performing better I assume that tail recursion optimization does have an effect here (see Phil's answer, if the Java version is rewritten to use a loop instead of recursion, it performs equally again).