score display

public class Counter extends Actor. I want it to appear on my GameOverScreen
{
    int score = 0;
    /**
     * Act - do whatever the Counter wants to do. This method is called whenever
     * the 'Act' or 'Run' button gets pressed in the environment.
     */
    public void act() 
    {
        setImage(new GreenfootImage("Score : " + score, 24, greenfoot.Color.RED, greenfoot.Color.BLACK));
    } 
     
    public void addScore()
    {
        score++;
    }
}

public class GameScreen extends World
{
    private int delay = 0;
    Counter counter = new Counter();
    public int lifeCounter = 3;
     
    private Lives lives1;
    private Lives lives2;
    private Lives lives3;
    /**
     * Constructor for objects of class GameScreen.
     * 
     */
    public GameScreen()
    {    
        // Create a new world with 600x400 cells with a cell size of 1x1 pixels.
        super(600, 400, 1, false); 
        
        prepare();
    }
    
    public Counter getCounter()
    {
      return counter;  
    }

public class Laser extends Actor
{
public void act() 
    {
        if(!toRemove)
        {
            setLocation(getX()+vx,getY());
            Actor actor=getOneIntersectingObject(Enemy.class);
            if(actor!=null)
            {
                GameScreen gameScreen = (GameScreen)getWorld();
                Counter counter = gameScreen.getCounter();
                counter.addScore();
                ((Enemy)actor).destroyed();
                Greenfoot.playSound("Explosion.wav");
            }
}