本题中，通过菜单“Connect”显示一个对话框，单击“ok”按钮后，所填写的内容就会传回到主窗口并显示出来。
import java. awt. * ;
import java. awt. event. * ;
import javax. swing. * ;
public class java3 extends JFrame implements ActionListener
public java3()
setTitle("java3");
setSize(300,300);
addWindowListener(new WindowAdapter()
public void windowClosing(WindowEvent e)
System. exit(0);

);
JMenuBar mbar=new JMenuBar();
setJMenuBar(bar);
JMenu fileMenu=new JMenu("File");
mbar. add(fileMenu);
connectItem=new JMenuItem("Connect");
connectltem. 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 java3();
f. show();

private ConnectDialog dialog=null;
private JMenuItem connectltem;
private JMenuItem exitItem;

class Connectlnfo
public String username;
public String password;
public ConneetInfo(String u, String p)
username=u; password=p;


class ConnectDialog extends JDialog implements ActionListener
public ConnectDialog()
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);

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(faIse);

public void 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;

private JTextField username;
private JPasswordField password;
private boolean ok;
private JButton okButton;
private JButton cancelButton;