class Square
{
  final String fCoordinate;
  final Position fOver;
  final Position fAt;
  boolean fOccupied;

  Square(String coordinate, Position over, Position at)
  {
    fCoordinate = coordinate;
    fOver = over;
    fAt = at;
    fOccupied = false;
  }

  void pickUp(RobotArm arm)
  {
    if (!fOccupied)
      throw new Problem("Cannot pick up at unoccupied square "+fCoordinate);

    arm.move(fOver);
    arm.grip(Game.GRIP_OPEN);
    arm.move(fAt);
    arm.grip(Game.GRIP_CLOSE);
    arm.move(fOver);

    fOccupied = false;
  }

  void putDown(RobotArm arm)
  {
    if (fOccupied)
      throw new Problem("Cannot put down on occupied square "+fCoordinate);

    arm.move(fOver);
    arm.move(fAt);
    arm.grip(Game.GRIP_OPEN);
    arm.move(fOver);

    fOccupied = true;
  }

  boolean equals(String coordinate)
  {
    return fCoordinate.equals(coordinate);
  }

  public String toString()
  {
    return fCoordinate;
  }
}