如何使用根面板

myGlassPane = new MyGlassPane(...);
changeButton.addItemListener(myGlassPane);
frame.setGlassPane(myGlassPane);
...
class MyGlassPane extends JComponent
                  implements ItemListener {
    ...
    //响应更改按钮点击事件。
    public void itemStateChanged(ItemEvent e) {
        setVisible(e.getStateChange() == ItemEvent.SELECTED);
    }
...
}

... //在玻璃板的鼠标监听器的实现中：
public void mouseMoved(MouseEvent e) {
    redispatchMouseEvent(e, false);
}

... /* mouseDragged, mouseClicked, mouseEntered,
    * mouseExited和mousePressed方法的实现与mouseMoved相同。 */...

public void mouseReleased(MouseEvent e) {
    redispatchMouseEvent(e, true);
}

private void redispatchMouseEvent(MouseEvent e,
                                  boolean repaint) {
    Point glassPanePoint = e.getPoint();
    Container container = contentPane;
    Point containerPoint = SwingUtilities.convertPoint(
                                    glassPane,
                                    glassPanePoint,
                                    contentPane);

    if (containerPoint.y < 0) { //不在内容窗格中
        //可能有特殊代码来处理菜单栏或非系统窗口装饰上的鼠标事件，
        //例如Java外观提供的装饰。
    } else {
        //鼠标事件可能发生在内容窗格上。
        //确定准确位于哪个组件上。
        Component component =
            SwingUtilities.getDeepestComponentAt(
                                    container,
                                    containerPoint.x,
                                    containerPoint.y);

        if ((component != null)
            && (component.equals(liveButton))) {
            //将事件转发到复选框上。
            Point componentPoint = SwingUtilities.convertPoint(
                                        glassPane,
                                        glassPanePoint,
                                        component);
            component.dispatchEvent(new MouseEvent(component,
                                                 e.getID(),
                                                 e.getWhen(),
                                                 e.getModifiers(),
                                                 componentPoint.x,
                                                 componentPoint.y,
                                                 e.getClickCount(),
                                                 e.isPopupTrigger()));
        }
    }

    //如果需要，更新玻璃板。
    if (repaint) {
        glassPane.setPoint(glassPanePoint);
        glassPane.repaint();
    }
}

protected void paintComponent(Graphics g) {
    if (point != null) {
        g.setColor(Color.red);
        g.fillOval(point.x - 10, point.y - 10, 20, 20);
    }
}