public void run(){
    //This reference must be final because it is
    // referenced from within an anonymous class
    // definition.
    final World world = new World(200,300);

    //Get a reference to the JFrame object that
    // is used to display the World.
    JFrame frame = world.getFrame();

    //Instantiate a new JButton object and
    // add it to the NORTH location in the
    // JFrame object.
    JButton button = new JButton(
                     "Click to make a turtle.");
    frame.getContentPane().add(
                     button,BorderLayout.NORTH);


    frame.pack();//VERY IMPORTANT