if (color == null) throw new IllegalArgumentException("No color.");
    public ChannelButton(String text, Color color, int index,                         boolean selected)    {        super(text, color);        if (color == null)             throw new IllegalArgumentException("No color.");        this.index = index;        setSelected(selected);        addMouseListener(new MouseAdapter() {            public void mousePressed(MouseEvent e) { onClick(e); }            public void mouseReleased(MouseEvent e) { onReleased(e); }        });    }