java applet正在运行但不正确

Question

为什么这个小程序不起作用？

import java.awt.*;
import java.awt.event.*;
import java.applet.*;
public class MenuDemo extends Applet implements ActionListener
{ 
    private TextField myTextField;
    private Frame myFrame;
    @Override
    public void init()
    { 
        myFrame = new Frame();
        myFrame.addWindowListener(new Terminator());
        myTextField = new TextField(20);
        add(myTextField);
        myFrame.setBounds(200,200,300,300);
        // place myMenuBar at top of myFrame
        MenuBar myMenuBar = new MenuBar();
        myFrame.setMenuBar(myMenuBar);

        Menu fileMenu = new Menu("File");
        myMenuBar.add(fileMenu);

        Menu editMenu = new Menu("Edit");
        myMenuBar.add(editMenu);
        MenuItem myMenuItem;

        myMenuItem = new MenuItem("Open");
        myMenuItem.addActionListener(this);
        fileMenu.add(myMenuItem);

        myMenuItem = new MenuItem("Close");
        myMenuItem.addActionListener(this);
        fileMenu.add(myMenuItem);

        myMenuItem = new MenuItem("Undo");
        myMenuItem.addActionListener(this);
        editMenu.add(myMenuItem);
        myFrame.show();
    } 
    @Override
    public void actionPerformed(ActionEvent e)
    { 
        if(e.getSource() instanceof MenuItem)
           myTextField.setText("Your Choice: "+ e.getActionCommand());
    } 
    public class Terminator extends WindowAdapter
    { 
        @Override
        public void windowClosing(WindowEvent e)
        { 
            myFrame.dispose();
        // use System.exit(0) for applications
        } 
    }
}