public void act(){
        if (Greenfoot.mouseClicked(this)){
            try{
                Class cls = Class.forName(type);
                tower = (Tower)cls.newInstance();               
            } catch (Exception e){
                System.err.println(e);
            }
            getWorld().addObject(tower, 0, 0);
        }
        if (tower != null && !tower.placed && tower.getWorld() != null){
            buy(tower);
        }
    }