Scala中是否有SoftHashMap？

import scala.collection.mutable.{Map,HashMap}
import scala.ref._


class SoftMap[K,V <: AnyRef] extends Map[K,V]
{
  class SoftValue[K,+V <: AnyRef](val key:K,value:V,queue:ReferenceQueue[V]) extends SoftReference(value,queue)

  private val map = new HashMap[K,SoftValue[K,V]]

  private val queue = new ReferenceQueue[V]

  override def += (kv: (K,V)): this.type =
  {
    processQueue
    val sv = new SoftValue(kv._1,kv._2,queue)
    map(kv._1) = sv
    this
  }

  private def processQueue
  {
    while (true)
    {
      queue.poll match
      {   
        case Some(sv:SoftValue[K,_]) => map.remove(sv.key)
        case _ => return
      }
    }
  }


  override def get(key: K): Option[V] = map.get(key) match
  {
    case Some(sv) => sv.get match
      { case v:Some[_] => v
        case None => {map.remove(key); None} }
    case None => None
  }



  override def -=(key: K):this.type =
  {
    processQueue
    map.remove(key)
    this
  }

  override def iterator: Iterator[(K,V)] =
  {
    processQueue
    map.iterator.collect{ case (key,sv) if sv.get.isDefined => (key,sv.get.get) }
  }

  override def empty:SoftMap[K,V] = new SoftMap[K,V]

  override def size = {processQueue; map.size}
}