代码如下：
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class DataExchangeTest extends JFrame
   implements ActionListener{
      private ConnectDialog dialog = null;
      private JMenuItem connectItem;
      private JMenuItem exitItem;
      
      public DataExchangeTest(){
         setTitle("DataExchangeTest");
         setSize(200,200);
         
         addWindowListener(new WindowAdapter(){
            public void windowClosing(WindowEvent e){
               System.exit(0);
            }
         });
         
         JMenuBar mbar = new JMenuBar();
         setJMenuBar(mbar);
         JMenu fileMenu = new JMenu("File");
         mbar.add(fileMenu);
         connectItem = new JMenuItem("Connect");
         connectItem.addActionListener(this);//
         fileMenu.add(connectItem);
         exitItem = new JMenuItem("Exit");
         exitItem.addActionListener(this);
         fileMenu.add(exitItem);
      }
      
      public void actionPerformed(ActionEvent evt){
         Object source = evt.getSource();
         if(source == connectItem){
            ConnectInfo transfer = new ConnectInfo("yourname","pw");
            if(dialog == null){
               dialog = new ConnectDialog(this);
            if(dialog.showDialog(transfer)){
               String uname = transfer.username;
               String pwd = transfer.password;
               Container contentPane = getContentPane();
               contentPane.add(new JLabel("username="+uname+
               ",password="+pwd),"South");
               validate();
            }
            
           
         }else if(source == exitItem)
            System.exit(0);
      }

    public static void main(String [] args){
         JFrame f = new DataExchangeTest();
         f.show();
    }
      
      
}

class ConnectInfo{
   public String username;
   public String password;
   public ConnectInfo(String u,String p){
      username = u;
      password = p;
   }
}

class ConnectDialog extends JDialog
   implements ActionListener{
      private JTextField username;
      private JPasswordField password;
      private boolean ok;
      private JButton okButton;
      private JButton cancelButton;
      
      public ConnectDialog(JFrame parent){
         super(parent,"Connect",true);
         Container contentPane = getContentPane();
         JPanel p1 = new JPanel();
         p1.setLayout(new GridLayout(2,2));
         p1.add(new JLabel("User name:"));
         p1.add(username = new JTextField(""));
         p1.add(new JLabel("Password:"));
         p1.add(password = new JTextField(""));
         contentPane.add("Center",p1);
         
         Panel p2 = new Panel();
         okButton = addButton(p2,"OK");
         cancelButton = addButton(p2,"Cancel");
         contentPane.add("South",p2);
         setSize(240,120);
      }
      
      JButton addButton(Container c, String name){
         JButton button = new JButton(name);
         button.addActionListener(this);
         c.add(button);
         
         return button;
      }
      
      public void actionPerformed(ActionEvent evt){
         Object source = evt.getSource();
         if(source == okButton){
            ok = ture;
            setVisible(false);
         }else if(source==cancelButton){
            setVisible(false);
         }
      }
      
      public boolean showDialog(ConnectInfo transfer){
         username.setText(transfer.username);
         password.setText(transfer.password);
         ok = false;
         show();
         if(ok){
            transfer.username = username.getText();
            transfer.password = new String(password.getPassword());
         }
         return ok;
      }
   
}
多谢各位！！！

haha,给分给分

p1.add(password = new JTextField(""));
 contentPane.add("Center",p1);

------------------------------------
p1.add(password=new JPasswordField("应该是密码框组件"))

就是，子类的句柄无法指向父类吧，编译错误！

错误很多:现为如下,可运行!
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class DataExchangeTest extends JFrame implements ActionListener{
      private ConnectDialog dialog = null;
      private JMenuItem connectItem;
      private JMenuItem exitItem;

  public static void main(String[] args){
JFrame f=new DataExchangeTest();
f.show();
  }
      public DataExchangeTest(){
         setTitle("DataExchangeTest");
         setSize(200,200);
         
         addWindowListener(new WindowAdapter(){
            public void windowClosing(WindowEvent e){
               System.exit(0);
            }
         });
         
         JMenuBar mbar = new JMenuBar();
         setJMenuBar(mbar);
         JMenu fileMenu = new JMenu("File");
         mbar.add(fileMenu);
         connectItem = new JMenuItem("Connect");
         connectItem.addActionListener(this);//
         fileMenu.add(connectItem);
         exitItem = new JMenuItem("Exit");
         exitItem.addActionListener(this);
         fileMenu.add(exitItem);
      }
      
  public void actionPerformed(ActionEvent evt){
         Object source = evt.getSource();
         if(source == connectItem){
            ConnectInfo transfer = new ConnectInfo("yourname","pw");
            if(dialog == null){
               dialog = new ConnectDialog(this);
            if(dialog.showDialog(transfer)){
               String uname = transfer.username;
               String pwd = transfer.password;
               Container contentPane = getContentPane();
               contentPane.add(new JLabel("username="+uname+",password="+pwd),"South");
               validate();
            }
         }else if(source == exitItem)
            System.exit(0);
      }

}

class ConnectInfo{
   public String username;
   public String password;
   public ConnectInfo(String u,String p){
      username = u;
      password = p;
   }
}

class ConnectDialog extends JDialog implements ActionListener{
      private JTextField username;
      private JPasswordField password;
      private boolean ok;
      private JButton okButton;
      private JButton cancelButton;
      
      public ConnectDialog(JFrame parent){
         super(parent,"Connect",true);
         Container contentPane = getContentPane();
         JPanel p1 = new JPanel();
         p1.setLayout(new GridLayout(2,2));
         p1.add(new JLabel("User name:"));
         p1.add(username = new JTextField(""));
         p1.add(new JLabel("Password:"));
         p1.add(password = new JPasswordField(""));
         contentPane.add("Center",p1);
         
         Panel p2 = new Panel();
         okButton = addButton(p2,"OK");
         cancelButton = addButton(p2,"Cancel");
         contentPane.add("South",p2);
         setSize(240,120);
      }
      
      private JButton addButton(Container c, String name){
         JButton button = new JButton(name);
         button.addActionListener(this);
         c.add(button);
         return button;
      }
      
      public void actionPerformed(ActionEvent evt){
         Object source = evt.getSource();
         if(source == okButton){
            ok = true;
            setVisible(false);
         }else if(source==cancelButton){
            setVisible(false);
         }
      }
      
      public boolean showDialog(ConnectInfo transfer){
         username.setText(transfer.username);
         password.setText(transfer.password);
         ok = false;
         show();
         if(ok){
            transfer.username = username.getText();
            transfer.password = new String(password.getPassword());
         }
         return ok;
      }
}
}

判断对象类型使用instanceof。