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

/**
 * Write a description of class InvadersWorld here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class InvadersWorld  extends World
{
    
    /**
     * Constructor for objects of class InvadersWorld.
     * 
     */
    public InvadersWorld()
    {    
      
        super(600, 400, 1); 
        setBackground("background.png");
    }
    
    public void act()
    {
        //bla
    }
}