对于 Java GUI 作业额外的功劳,我正在尝试将几个面板添加到 JTabbedPane。实际上,它们是 JFrame,但我只是更改为扩展 JPanel 而不是 JFrame,并删除了 main()。无论如何,当我运行 main() 时,JTabbedPane 和两个面板都出现了,但是是分开的。我错过了什么?
   import javax.swing.*;
public class TabbedPane extends JFrame
{
    JPanel DayGui = new JPanel();
    JPanel OfficeAreaCalculator = new JPanel();
    JLabel firstLabel = new JLabel("First tabbed pane");
    JLabel secondLabel = new JLabel("Second tabbed pane");
    JTabbedPane tabbedPane = new JTabbedPane();
    // constructor
    public TabbedPane()
    {
        DayGui.add(firstLabel);
        OfficeAreaCalculator.add(secondLabel);
        tabbedPane.add("First Panel", DayGui);
        tabbedPane.add("Second Panel", OfficeAreaCalculator);
        add(tabbedPane);
    }
    public static void main(String[] args)
    {
        TabbedPane tab = new TabbedPane();
        tab.pack();
        tab.setVisible(true);
        JTabbedPane DayGui = new JTabbedPane();
        JTabbedPane OfficeAreaCalculator = new JTabbedPane();
        DayGui dg = new DayGui();
        OfficeAreaCalculator oac = new OfficeAreaCalculator();
    }
}