无法将JPanel实例传递给另一个类

Question

我创建了与记事本相同的菜单，并希望在点击新标签后添加新标签。 所以我创建了New()函数，返回类型为JPanel。但它并没有归还我必须工作的对象。

以下是代码：

class Notepad {

    public static void main(String []z){

        JFrame jf = new JFrame("J-Note");
        JTabbedPane jtab = new JTabbedPane();

        Menus menus = new Menus(jf, jtab);

        jf.add(jtab, BorderLayout.CENTER);

        Page pg = new Page();       
        //pg.getObject(jtab);
        jtab.add(pg, "Tag 1");      

        jf.setSize(700,400);        
        jf.setVisible(true);
        jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
};

class Menus {

    JTabbedPane jtab;
    JFrame jf;

    public Menus() {}

    public Menus(JFrame jf, JTabbedPane jtab) {

        this.jf   = jf;
        this.jtab = jtab;

        JMenuBar jmenuBar = new JMenuBar();         
        jf.add(jmenuBar, BorderLayout.NORTH);

        ////////////////////////////////////////////////////////////////////
        /* Menu File: New, Open, Save, Save As, Page setup, Print, Exit. */
        JMenuItem New, Open, Save, Save_As, Page_SetUp, Print, Exit;

        JMenu jmenuFile   = new JMenu("File");
        jmenuBar.add(jmenuFile);

        New = new JMenuItem("New");
        jmenuFile.add(New);
        New.setActionCommand("N");
        New.addActionListener(new File(jtab));

        Open = new JMenuItem("Open");
        jmenuFile.add(Open);
        Open.setActionCommand("O");
        Open.addActionListener(new File());
    }
}

class Page extends JPanel {

    public String str = "Harshad";
    //JTabbedPane jtab;
    JPanel jp;
    JLabel jl;
    public JTextArea jtxtArea;

    public Page () {

        BorderLayout brLayout = new BorderLayout();     
        brLayout.setHgap(20);

        setLayout(brLayout);

        jp = new JPanel();
        jp.setOpaque(true);
        jp.setBackground(Color.GRAY);
        add(jp, BorderLayout.WEST);

        jl = new JLabel("1");   
        jp.add(jl);

        jtxtArea = new JTextArea();
        //jtxtArea.setOpaque(true);
        //jtxtArea.setBackground(Color.GREEN);
        add(jtxtArea, BorderLayout.CENTER);
    }
}


class File implements ActionListener {

    JTabbedPane jtab;

    public File() {}

    public File(JTabbedPane jtab) {

        this.jtab = jtab;
    }

    public void actionPerformed(ActionEvent e) {

        String s = e.getActionCommand();
        char ch = s.charAt(0);      

        //JOptionPane.showMessageDialog(new JFrame(),"You Clicked "+e.getActionCommand());

        switch(ch) {

            case 'O':   Page p = New();
                        JOptionPane.showMessageDialog(new JFrame(),"Page str: "+p.str);
            break;

            case 'N':   New();
            break;

            default:    JOptionPane.showMessageDialog(new JFrame(),"Operation Not Found.");
            break;
        }
    }

    Page New() {

        Page pg = new Page();
        jtab.add(pg,"Tab 2");

        return p;
    }

    void open() {

        try {

            FileDialog fd = new FileDialog(new JFrame(), "Select a File to Open");
            fd.setVisible(true);

            if(fd.getFile()==null)          
                return;

            String fname = fd.getDirectory() + fd.getFile();                        
            FileInputStream fin = new FileInputStream(fname);
            int size = fin.available();         
            byte []data = new byte[size];
            fin.read(data);
            String str = new String(data);          
            //JOptionPane.showMessageDialog(new JFrame(),"Panel: "+str);

            Page p = New();         
            p.jtxtArea.setText(str);

        }
        catch(IOException ioex) {

            JOptionPane.showMessageDialog(new JFrame(),"You Clicked "+ioex);
        }

    }
};