Comparing different Scala Map performance

MapCompare.scala

import scala.collection.concurrent
import scala.collection.immutable._


val concurrentTrieMap: concurrent.Map[String, String] = concurrent.TrieMap.empty
var immutableMap: Map[String, String] = Map.empty
var hashMap: HashMap[String, String] = HashMap.empty

def time[R](block: => R): String = {
  val t0 = System.nanoTime()
  block
  val t1 = System.nanoTime()
  (t1 - t0) + "ns"
}

val r = new scala.util.Random(31)
val keys = 1 to 100 map (_ => r.alphanumeric.take(3).mkString)
val values = 1 to 100 map (_ => r.alphanumeric.take(100).mkString)
println("populating time: ")
print("concurrentTrieMap ",
  time {
    keys.foreach { key =>
      values.foreach { value =>
        concurrentTrieMap.put(key, value)
      }
    }
  })

print("immutableMap ",
  time {
    immutableMap = (for {
      key <- keys
      value <- values
    } yield key -> value) (collection.breakOut)
  })

print("hashMap ",
  time {
    hashMap = (for {
      key <- keys
      value <- values
    } yield key -> value) (collection.breakOut)
  })

// lookup
println("Lookup time ")
val runs = 1 to 1000000
val keySequence = runs map (_ => keys(r.nextInt(100)))
print("concurrentTrieMap ",
  time {
    keySequence foreach { oneKey =>
      concurrentTrieMap.get(oneKey)
    }
  })

print("immutableMap ",
  time {
    keySequence foreach { oneKey =>
      immutableMap.get(oneKey)
    }
  }
)

print("hashMap ",
  time {
    keySequence foreach { oneKey =>
      hashMap.get(oneKey)
    }
  }
)