Multi Worlds problem

import java.util.List;
import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)

/**
 * The Robot of the game. It moves and bounces off the walls and the paddle.
 * 
 * @author  
 * @version (Version 1.0)
 */
public class Robot extends Actor
{

    private int points = 0;
    private Counter counter; 
    private HealthBar healthBar;

    private int deltaX; //  delat is movement in the x direction
    private int deltaY; //  delta is movement in the y direction
    private int count = 2;
    //private int CircleWorld;
    //private int SquareWorld;
    //private SquareWorld squareWorld;
    private int level;
   
    private boolean fixed = true; // ????

    public Robot(Counter c, HealthBar hb)
    {
        counter = c;
        healthBar = hb;
    }

    public Robot()
    {
      level = 1;
    }

    /**
     * Act. Move the Robot if we're not fixed to paddle.
     */
    public void act()
    {
        if (!fixed)
        {
            move();
            makeSmoke();
            checkEggs();
            checkOut();
            checkNextLevel();
            
        }
    }

    /**
     * Move the Robot. Thencheck what we've hit.
     */
    public void move()
    {
        setLocation (getX() + deltaX, getY() + deltaY);
        checkPaddle();
        checkWalls();
    }

    /**
     * Check whether we've hit one of the three walls. Reverse direction
     */
    private void checkWalls()
    {
        if (getX() == 0 || getX() == getWorld().getWidth()-1) {
            deltaX = -deltaX;
        }
        if (getY() == 0) {
            deltaY = -deltaY;
        }
    }

    /**
     * Check whether we're out (bottom of screen).
     */
    private void checkOut()
    {   
        if (getY() == getWorld().getHeight()-1) 
        {
            List<Paddle> paddles = getWorld().getObjects(Paddle.class);
            Robot newRobot = new Robot(counter, healthBar);
            getWorld().addObject(newRobot, paddles.get(0).getX(), paddles.get(0).getY() - 35);
            paddles.get(0).setNewRobot(newRobot);
            getWorld().removeObject(this);
        }
    }

    /**
     * Check whether we have hit an egg, and make the egg disappear if we have
     */

    private void checkEggs()
    {
        Actor egg = getOneIntersectingObject(goldEgg.class);
        if (egg != null)
        {
            getWorld().removeObject(egg);
            deltaY = -deltaY;
            counter.add(5);
        }

        egg = getOneIntersectingObject(yellowEgg.class);
        if (egg != null)
        {
            getWorld().removeObject(egg);
            deltaY = -deltaY;
            counter.add(3);
        }
        
        egg = getOneIntersectingObject(redEgg.class);
        if (egg != null)
        {
            getWorld().removeObject(egg);
            deltaY = -deltaY;
            counter.add(1);
        }
        
        egg = getOneIntersectingObject(blueEgg.class);
        if (egg != null)
        {
            getWorld().removeObject(egg);
            deltaY = -deltaY;
            healthBar.add(-10);
        }

        //if (counter.getValue() >= 60) {
        //     gameOver();
    }

    private void checkPaddle()
    {
        Actor paddle = getOneIntersectingObject(Paddle.class);
        if (paddle != null) {
            deltaY = -deltaY;
            int offset = getX() - paddle.getX();
            deltaX = deltaX + (offset/10);
            if (deltaX> 7) {
                deltaX = 7;
            }
            if (deltaX < -7) {
                deltaX = -7;
            }
            //SquareWorld mySquareWorld = (SquareWorld) getWorld();
            //mySquareWorld.score();

        }
    }

    /**
     * Move the Robot a given distance sideways
     */
    public void move(int dist)
    {
        setLocation (getX() + dist, getY());

    }

    /**
     * Put out a puff of smoke (only on every second call).
     */
    private void makeSmoke()
    {
        count--;
        if (count == 0) {
            getWorld().addObject ( new Smoke(), getX(), getY());
            count = 2;
        }
    }

    /**
     * Release the Robot from the paddle.
     */
    public void release()
    {
        deltaX = Greenfoot.getRandomNumber(11) - 5;
        deltaY = -5;
        fixed = false;
    }
    
    /**
     * Check whether we should go to the next level, and if yes, start the next level.
     */
    private void checkNextLevel()
    {
         if (getX() == getWorld().getWidth()-1) {
            if (level == 1) {
                level = 2;
                getWorld().removeObject(this);
                Greenfoot.setWorld(new SquareWorld(this));
            }
            else {
                level = 1;
                getWorld().removeObject(this);
                Greenfoot.setWorld(new CircleWorld(this));
            }
        }
    }
}