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

public class Shot  extends Actor
{
    // field with the Objectreference to the rocket that shot me
    private Rocket myship;

    public Shot(Rocket myShip)
    {
        this.myship = myship;
    }
    public void act() 
    {
        doShotThings();
    } 

    public void doShotThings() {
        int ypos = getY();
        if (ypos > 0) {
            ypos = ypos - 5;
            setLocation(getX(), ypos);
            Actor rock = getOneIntersectingObject(Asteroid.class);
            if (rock != null) {
                // We've hit an asteroid!
                updateScore();
                getWorld().removeObject(rock);
                getWorld().removeObject(this);
            }
        }
        else {
            // I reached the top of the screen
            getWorld().removeObject(this);
        }
    }
    private void updateScore()
    {
       //4: Hier maak je eerst een Objectreferentie naar de Spacewereld. Daar vraag je dan de getCounter methode op. 
        Space space = (Space) getWorld();
        space.getCounter(); 
    }
}

final Rocket reallyARocket = (Rocket)rocket;
reallyARocket.fly();

Space space = (Space) getWorld();

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

public class Space2 extends World
{
    
   //1: hier een veld maken die de Objectreferentie naar de Counter kan opslaan
    private Counter counter;
    
    /**
     * Constructor for objects of class Space.
     */
    
    public Space2()
    {    
        // Create a new world with 600x400 cells with a cell size of 1x1 pixels.
        super(600, 400, 1); 
        addObject(new Rocket(), 300, 340);
        //2: hier de Objectreferentie van 1: gebruiken om een nieuwe counter te maken
        counter = new Counter();
        addObject(counter, 20,20);
        
    }

    
        //3: hier maak je een methode die de counter ophaalt.
        // Noem de methode maar: public Counter getCounter()
    public void getCounter() {
        counter.bumpCount(0);
        }
        
    
    /**
     * Prepare the world for the start of the program. That is: create the initial
     * objects and add them to the world.
     */
    private void prepare()
    {
    }
    
    public void act()
    {
       spawnAsteroid();
    }
    public void spawnAsteroid() {
         if (Greenfoot.getRandomNumber(1000) < 3) {
            addObject(new Asteroid(), 0, 20);
        }
    }
    public class Counter  extends Actor
    
    {
    private int totalCount = 0;

    public Counter()
    {
        setImage(new GreenfootImage("0", 20, Color.WHITE, Color.BLACK));
    }

    /**
     * Increase the total amount displayed on the counter, by a given amount.
     */
    public void bumpCount(int amount)
    {
        totalCount += amount;
        setImage(new GreenfootImage("" + totalCount, 20, Color.WHITE, Color.BLACK));
        if (totalCount >= 10) {
        Greenfoot.setWorld(new Tussenscherm());
        }
    }
    }
}

public class Space2 extends Space {}

if (timer <= 0) { Greenfoot.setWorld(new Space()); }

private void updateScore()
{
    //4: Hier maak je eerst een Objectreferentie naar de Spacewereld. Daar vraag je dan de getCounter methode op. 
    if (getWorld() instanceof Space) {
        Space space = (Space)getWorld();
        space.getCounter();
    }
    else if (getWorld() instanceof Space2) {
        Space2 space2 = (Space2)getWorld();
        space2.getCounter(); 
    }
}

private void updateScore() {
    ((SpaceWorld)getWorld()).getCounter();
}