JPanels未添加到JTabbedPane

对于我的功课，我要创建一个JTabbedPane并添加两个Jpanels。我感觉自己非常接近，但是仍然无法编译。当我运行它时，两个JPanels都打开，但是JTabbedPane没有打开。我收到很多未知源错误。我怀疑这时我在JPanels本身中遇到了问题，因为它们最初是JFrames，并且我尝试（我认为未成功）将JFrames转换为JPanels。

JTabbedPaneAssignment应该创建JTabbedPane，并在一个选项卡上使用DayGui应用程序，在另一个选项卡上使用OfficeAreaCalculator填充两个窗格。我在这里仅包括JTabbedPaneAssignment和DayGui类。如果它的代码太多，我对此表示歉意，我删节了很多我认为无关紧要的内容，但可能仍然太多了。

这是调用类JTabbedPaneAssignment

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class JTabbedPaneAssignment extends JPanel
{
    public JTabbedPaneAssignment()
    {
        //super(new GridLayout(1, 1));

        JTabbedPane tabbedPane = new JTabbedPane();
        DayGui pnlDay = new DayGui();
        OfficeAreaCalculator  pnlOffice = new OfficeAreaCalculator ();
        this.add(tabbedPane);

        JPanel panel1 = new JPanel();
        JPanel panel2 = new JPanel();
        tabbedPane.add(panel1,"First panel");
        tabbedPane.add(panel2,"Second panel");


        //JComponent panel1 = makeTextPanel("Pane #1");
        panel1.setPreferredSize(new Dimension(300, 150));
        tabbedPane.addTab("DayGui", panel1);
        tabbedPane.setMnemonicAt(0, KeyEvent.VK_1);

        //JComponent panel2 = makeTextPanel("Pane #2");
        panel2.setPreferredSize(new Dimension(410, 50));
        tabbedPane.addTab("OfficeAreaCalculator", panel2);
        tabbedPane.setMnemonicAt(1, KeyEvent.VK_2);
        add(tabbedPane);
    }

    protected JComponent makeTextPanel(String text)
    {
        JPanel panel = new JPanel(false);
        JLabel filler = new JLabel(text);
        filler.setHorizontalAlignment(JLabel.CENTER);
        panel.setLayout(new GridLayout(1, 1));
        panel.add(filler);
        return panel;
    }

    // Create JTabbedPane
    private static void createAndShowGUI()
    {
        // Create and set up the window.
        JFrame frame = new JFrame("JTabbedPane");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(new JTabbedPaneAssignment(), BorderLayout.CENTER);
        JTabbedPane DayGui = new JTabbedPane();
        JTabbedPane OfficeAreaCalculator = new JTabbedPane();
        frame.pack();
        frame.setVisible(true);
    }


    public static void main(String[] args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                createAndShowGUI();
            }
        });
    }
}

这是DayGui课。它最初是作为JFrame开始的，但我正在尝试将其转换为JPanel。我认为我的问题在这段代码中，但我不知道

import java.awt.*;
import java.awt.event.*;

import javax.swing.*;

//public class DayGui extends JPanel
public class DayGui extends JPanel
{
    private JPanel dayPanel;
    private JButton cmdGood;
    private JButton cmdBad;

    public DayGui()
    {
        //dayPanel = new JPanel("Messages");

        cmdGood = new JButton("Good");
        cmdBad = new JButton("Bad");

        Container c = dayPanel.getRootPane();
        c.setLayout(new FlowLayout());

        c.add(cmdGood);
        c.add(cmdBad);

        dayPanel.setSize(300, 150);

        ButtonsHandler bhandler = new ButtonsHandler();
        cmdGood.addActionListener(bhandler);
        cmdBad.addActionListener(bhandler);

        dayPanel.setVisible(true);
        dayPanel.getRootPane().setBackground(Color.CYAN);

    }

    class ButtonsHandler implements ActionListener
    {
        public void actionPerformed(ActionEvent e)
        {
            if (e.getSource() == cmdGood)
                JOptionPane.showMessageDialog(null, "Today is a good day!",
                        "Event Handler Message",
                        JOptionPane.INFORMATION_MESSAGE);
            if (e.getSource() == cmdBad)
                JOptionPane.showMessageDialog(null, "Today is a bad day!",
                        "Event Handler Message",
                        JOptionPane.INFORMATION_MESSAGE);
        }
    }

}