Question

I have a java.util.Treemap[Long, Int] in Scala. What I need to do is convert the values in the Treemap into an Array[Int].

I can either get an Iterator[Int] or Collection[Int] from the TreeMap, but I’m not sure how to convert these into an Array[Int].

Any suggestions would be appreciated.

Answer 1

The problem with t.values.toArray is that java.util.Collection already has a toArray() method, which is why it returns an Integer[] which looks like an Array[AnyRef] to Scala. If Java didn’t have such a method, the implicit in JavaConversions would kick in and covert it to to an Iterable[Int] before building the Array. So you can either call the coversion explicitly or give a type hint:

import collection.JavaConversions._    

(t.values: Iterable[Int]).toArray

or alternatively

import collection.JavaConverters._

t.values.asScala.toArray

On my machine these are over twice about 30 times as fast as using toMap, for a 1000-entry TreeMap.