public void act() 
  {

      if (Greenfoot.isKeyDown("q"))
      {
          getWorld().addObject(new GelberStein(), 1,0); 
          Greenfoot.delay(2);
      }
      
      if (Greenfoot.isKeyDown("w"))
      {
          getWorld().addObject(new GelberStein(), 2,0); 
          Greenfoot.delay(2);
      }
      
      if (Greenfoot.isKeyDown("e"))
      {
          getWorld().addObject(new GelberStein(), 3,0); 
          Greenfoot.delay(2);
      }
      
      if (Greenfoot.isKeyDown("r"))
      {
          getWorld().addObject(new GelberStein(), 4,0); 
          Greenfoot.delay(2);
      }
      
      if (Greenfoot.isKeyDown("t"))
      {
          getWorld().addObject(new GelberStein(), 5,0); 
          Greenfoot.delay(2);
      }
      
      if (Greenfoot.isKeyDown("z"))
      {
          getWorld().addObject(new GelberStein(), 6,0); 
          Greenfoot.delay(2);
      }
      
      if (Greenfoot.isKeyDown("u"))
      {
          getWorld().addObject(new GelberStein(), 7,0); 
          Greenfoot.delay(2);
      }
    
      aktion ();
    
  }