Floor.java

public class Floor {
  enum State { NO_ONE_WAITING, PASSENGERS_WAITING, LOADING }
  
  private int passengersWaiting = 0;
  private State state = State.NO_ONE_WAITING;

  synchronized public void waitForElevator(String msg) {
    if (state == State.LOADING) {
      try {
        wait();
      } catch (InterruptedException ex) {
      }
    }

    passengersWaiting++;
    System.out.println(msg);

    if (state == State.NO_ONE_WAITING) {
      this.state = State.PASSENGERS_WAITING;
      notifyAll();
    }
  }

  synchronized public void getOnOffElevator(String msg) {
    if (state != State.LOADING) {
      try {
        wait();
      } catch (InterruptedException ex) { }
    }

    passengersWaiting--;
    System.out.println(msg);

    if (passengersWaiting == 0) {
      this.state = State.NO_ONE_WAITING;
      notifyAll();
    }
  }

  synchronized public void elevatorArrives(String msg) {
    if (state == State.LOADING) {
      try {
        wait();
      } catch (InterruptedException ex) { }
    }

    System.out.println(msg);

    if (state == State.PASSENGERS_WAITING) {
      this.state = State.LOADING;
    } else {
      this.state = State.NO_ONE_WAITING;
    }
    notifyAll();
  }

  synchronized public void elevatorLeaves(String msg) {
    if (state != State.NO_ONE_WAITING) {
      try {
        wait();
      } catch (InterruptedException ex) { }
    }

    System.out.println(msg);
  }
}

Floor.scala

import scala.actors._
import scala.actors.Actor._

class Floor(floorNum: int) extends Actor {
  private var passengersWaitingToGetOn = List[(Passenger, Floor)]()
  private var passengersWaitingToGetOff = List[Passenger]()
  
  def act() = {
    loop {
      react {
        case (passenger: Passenger, floor: Floor) =>
          passengersWaitingToGetOn = (passenger, floor) :: passengersWaitingToGetOn
          println(passenger + " waiting for elevator at " + this)
          
        case (passenger: Passenger) =>
          passengersWaitingToGetOff = passenger :: passengersWaitingToGetOff
          println(passenger + " on elevator to " + this)

        case (elevator: Elevator) =>
          for (passenger <- passengersWaitingToGetOff) {
            println(passenger + " getting off at " + this)
          }
          passengersWaitingToGetOff = List[Passenger]()

          for ((passenger, floor) <- passengersWaitingToGetOn) {
            println(passenger + " getting on at " + this)
            floor ! passenger
          }
          passengersWaitingToGetOn = List[(Passenger, Floor)]()

          elevator ! "loaded"
        case msg =>
          println("Unhandled message: " + msg)
      }
    }
  }

  override def toString() = "Floor " + floorNum
}