setBorder(BorderFactory.createLineBorder(Color.GRAY, 2));
    BrowserCanvas(BrowserModel model, BrowserUI view)    {        if (model == null) throw new NullPointerException("No model.");        if (view == null) throw new NullPointerException("No view.");        this.model = model;        this.view = view;        charWidth = getFontMetrics(getFont()).charWidth('m');        setDoubleBuffered(true);        setBorder(BorderFactory.createLineBorder(Color.GRAY, 2));        dragging = false;        addMouseListener(this);        addMouseMotionListener(this);    }