Scala unexpected stack overflow

I've written this basic program in Scala :

import scala.collection.mutable.HashMap

object HelloWorld {

  val treasureMap = new HashMap[BigInt, BigInt]

  def main(args: Array[String]) {
    println(fibCache(10))
  }

  def fibCache(n: BigInt): BigInt = {
    if (n == 0 || n == 1) {
      return n
    }
    return treasureMap.getOrElseUpdate(n, fibCache(n - 1) + fibCache(n - 2))
  }
}

and I would expect that with really large values, I'd have an OutOfMemoryError or something, but instead I see this:

Exception in thread "main" java.lang.StackOverflowError
    at java.math.BigInteger.compareMagnitude(Unknown Source)
    at java.math.BigInteger.compareTo(Unknown Source)
    at scala.math.BigInt.compare(BigInt.scala:141)
    at scala.math.BigInt.$less$eq(BigInt.scala:145)
    at scala.math.BigInt.fitsInLong(BigInt.scala:130)
    at scala.math.BigInt.hashCode(BigInt.scala:120)
    at scala.runtime.BoxesRunTime.hashFromNumber(Unknown Source)
    at scala.collection.mutable.HashTable$HashUtils$class.elemHashCode(HashTable.scala:366)
    at scala.collection.mutable.HashMap.elemHashCode(HashMap.scala:43)
    at scala.collection.mutable.HashTable$class.findEntry(HashTable.scala:108)
    at scala.collection.mutable.HashMap.findEntry(HashMap.scala:43)
    at scala.collection.mutable.HashMap.get(HashMap.scala:63)
    at scala.collection.mutable.MapLike$class.getOr开发者_C百科ElseUpdate(MapLike.scala:186)
    at scala.collection.mutable.HashMap.getOrElseUpdate(HashMap.scala:43)

Can someone help explain why? Also, is there a runtime setting I can use to alleviate this? Will -Xss help?

A StackOverflowError is a variation on the theme of running out of memory, it's just being precise about exactly which memory area has run out.

So yes, -Xss will help, but there's a better way....

This page has several alternative implementations that you can try: http://en.literateprograms.org/Fibonacci_numbers_(Scala)

You'll want to use the tail-recursive or stream-based variant to keep the stack size down.