Elevator design challenge [closed]

I need to strengthen my OOP skills and hence I thought to implement an Elevator simulator. At first what seem to be a simple design has grown into a complete mess and has left me confused about my knowledge of OOP. Below is the implementation classes.

/**
 * 1. User enter the elevator.
 * 2. Elevator checks the maximum capacity.
 * 3. User enters the floor number.
 * 4. Elevator registers the request.
 * 5. Elevator checks the next request and stops at that floor.
 * 6. When elevator is in the halt state the door opens.
 */

enum State {
  UP,
  DOWN,
  HALT
}

enum Command {
  ALARM,
  OPEN,
  CLOSE,
  GROUND,
  FIRST,
  SECOND
}

enum Floor {
  GROUND,
  FIRST,
  SECOND
}

interface Engine {
  public void moveTO(Floor floor);
}

interface Alarm {
  public void ring();
}

interface Sensor {
  public int getWeight();
  public int shouldCloseDoor();
}

final class Panel {
  private final Command[] commands;
  private final Elevator elevator;

  Panel(Command[] commands, Elevator elevator) {
    this.commands = commands;
    this.elevator = elevator;
  }

  public void onKeyPress(Command command) {
    if (command == Command.OPEN) {
      elevator.stop();
    } else if (command == Command.CLOSE) {
      elevator.move();
    } else if (command == Command.GROUND) {
      elevator.gotoFloor(Floor.GROUND);
    } else if (command == Command.FIRST) {
      elevator.gotoFloor(Floor.FIRST);
    } else if (command == Command.SECOND) {
      elevator.gotoFloor(Floor.SECOND);
    }
  }
}

final class Door {
  private boolean final open;

  Door() {
    open = false;
  }

  public void open() {
    if (open) return;
    try {
      Thread.sleep(1000); //1000 milliseconds is one second.
      open = true;
    } catch(InterruptedException ex) {
      Thread.currentThread().interrupt();
      close();
    }
  }

  public void close() {
    open = false;
  }
}

// Handle elevator logic. Here the assumption is that the elevator has to come
// back to ground floor if there are not any pending requests. There are two
// queues which handles the floor requests, the elevator keeps moving in the
// direction of the queue until that queue is not empty. If the elevator reaches 
// the top floor and there is no pending request then the elevator comes down to
// ground floor and comes to the halting state.
class Elevator {
  public static final int MAX_WEIGHT_ALLOWED = 1600;

  private final State state;
  private final Door door;
  private final Floor floor;
  private final Queue<Floor> queueUp;
  private final Queue<Floor> queueDOwn;
  private final Engine engine;
  private final Sensor sensor;
  private final Alaram alarm;

  Elevator(Door door, Engine engine, Sensor sensor, Alaram alarm) {
    this.door  = door;
    this.queueUp   = new Queue<Floor>();
    this.queueDown = new Queue<Floor>();
    this.state  = State.HALT
    this.floor  = Floor.ZERO;
    this.engine = engine;
    this.sensor = sensor;
    this.alarm  = alarm;
  }

  public void stop() {
    door.open();
    state = State.HALT;
    engine.stop();
    System.out.println("Elevator is in stopped state.");
  }

  private void moveUp() {
    while(!queueUp.isEmpty()) {
      floor = queueUp.dequeue();
      engine.moveTO(floor);
    }
    // All up requests are served.
    state = state.DOWN;
    gotoFloor(Floor.ZERO);
  }

  private void moveDown() {
    while(!queueDown.isEmpty()) {
      floor = queueUp.dequeue();
      engine.moveTO(floor);
    }
    // All down requests served.
    state = State.UP;
  }

  public void move() {
    if (sensor.getWeight() > Elevator.MAX_WEIGHT_ALLOWED) {
      alarm.ring();
      stop();
      return;
    }
    if (!sensor.shouldCloseDoor()) {
      alarm.ring();
      stop();
      return;
    }
    door.close();
    if (state == State.UP) {
      moveUp();
    } else if (state == State.DOWN) {
      moveDOwn();
    }
    // Both the queues are empty
    state = State.HALT;
    System.out.println("Elevator is moving to floor: " + );
  }

  public void gotoFloor(Floor nextFloor) {
    if (floor < nextFloor)
      queueDown.enqueue(floor);
    else
      queueUp.enqueue(floor);
    move();
  }
}


public class ElevatorSimulator {
  public static void main(String[] args) {
    Elevator elevator = new Elevator(
      new Door(), new Engine(), new Sensor(), new Alarm());
    Panel panel = new Panel(Command.values(), elevator);

    panel.onKeyPress(Command.OPEN);
    panel.onKeyPress(Command.CLOSE);
    panel.onKeyPress(Command.FIRST);
  }
}

I have heard that thinking and jotting down the requirement helps a lot and I tried it too but I think I completely failed in that scenario too.

Question

1. Good strategy to settle down on a set of requirements.
2. Avoid cognitive overload and concentrate on the high level design rather than switching to distracting details.
3. List and manage dependencies.
4. Overall how to approach a good design 🙂