dup1.scala

import javax.swing.SwingWorker

class A {
  def loadAll(f:(Int) => List[String]): List[String] = List("a")
  def getFriendsIds(page: Int): List[String] = List("a")
  def getFollowersIds(page: Int): List[String] = List("a")
}

class B {
  def setFollowers(followers: List[String]) {}
  def setFriends(friends: List[String]) {}
}

object Temp {
  def main(args: Array[String]): Unit = {
    val a = new A
    val b = new B
    new SwingWorker[List[String], Object] {
      def doInBackground = a.loadAll(a.getFollowersIds)
      override def done = b.setFollowers(get)
    }.execute

    new SwingWorker[List[String], Object] {
      def doInBackground = a.loadAll(a.getFriendsIds)
      override def done = b.setFriends(get)
    }.execute
  }
}

// How to eliminate duplication (four lines starting "new SwingWorker")?

// OK, here’s what I got working. Thanks everyone for the help.

    /** Background user fetcher */
    class BgUserFetcher(getter: Int => List[TwitterUserId], setter: List[String] => Unit) 
            extends SwingWorker[List[TwitterUserId], Object] {
      def doInBackground = twitterSession.loadAll(getter)
      override def done = setter(get.map(_.id.toString))
      execute
    }
   
    new BgUserFetcher(twitterSession.getFriendsIds  , streams.setFriendIds)
    new BgUserFetcher(twitterSession.getFollowersIds, streams.setFollowerIds)