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

/**
 * Write a description of class MyWorld here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class MyWorld extends World
{
    private int Counter = 0;
    private int SCROLL_SPEED = -3;
    /**
     * Constructor for objects of class MyWorld.
     * 
     */
    public MyWorld()
    {    
        // Create a new world with 600x400 cells with a cell size of 1x1 pixels.
        super(600, 400, 1); 
        prepare();
    }
    Counter counter = new Counter();
    public Counter getCounter()
    { 
        return counter; 
    }

    public void addPizza()
    {
        int speed = Greenfoot.getRandomNumber(3) + 1;               // random speed
        int y = Greenfoot.getRandomNumber(getHeight() - 50) + 25 ;  // random y location
        int direction = Greenfoot.getRandomNumber(80);               // random direction
        if (direction == 2)
        {
            Pizza pizza = new Pizza(-speed);        // make speed negative
            pizza.getImage().mirrorHorizontally();
            addObject(pizza, getWidth(), y);      // add fish to right edge
        }
    }

    public void addRocket()
    {
        int speed = Greenfoot.getRandomNumber(3) + 1;               // random speed
        int y = Greenfoot.getRandomNumber(getHeight() - 50) + 25 ;  // random y location

        int direction = Greenfoot.getRandomNumber(80);               // random direction
        if (direction == 2)  
        {
            Rocket rocket = new Rocket(-speed);        // make speed negative
            rocket.getImage().mirrorHorizontally();
            addObject(rocket, getWidth(), y);      // add fish to right edge
        }
    }

    public void act()
    {
        scrollBackground();
        addPizza();
        addRocket();
    }

    public void scrollBackground()
    {
        GreenfootImage copy = new GreenfootImage(getBackground());
        getBackground().drawImage(copy, SCROLL_SPEED, 0);
        getBackground().drawImage(copy, getBackground().getWidth()+ SCROLL_SPEED, 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()
    {

        Dolphin dolphin = new Dolphin();
        addObject(dolphin,56,196);
    }
}
[code]