public void checkLevel()
    {
        if(getObjects(Brick.class).isEmpty()) 
        {
            // remove ball from world. Reset into original location. removeObject(ball); does NOT work.
            removeObjects(getObjects(Ball.class)); 
            // reset to original location
            resetPosition();
            // increase level by 1 and call upon next level.
            level++;
            nextLevel();   
        }
    }