//LoginDialogDemo.javaimport java.awt.*;import javax.swing.*;import java.awt.event.*;public class LoginDialogDemo extends JFrame {  JButton button = new JButton("Click Me");  JPanel panel = new JPanel(new FlowLayout());  public LoginDialogDemo() {    final JFrame frame = this;    this.getContentPane().add(panel,BorderLayout.SOUTH);    panel.add(button);    button.addActionListener(new ActionListener()  {      public void actionPerformed(ActionEvent e) {        showLoginDialog(frame);      }    });    this.setSize(300,200);    this.setTitle("顯示登陸對話框");    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);    this.show();  }  void showLoginDialog(JFrame frame){    JPanel p = new JPanel(new GridLayout(0,1));    JTextField tfUserName = new JTextField();    JPasswordField tfPassword = new JPasswordField();    p.add(new JLabel("Username: "));    p.add(tfUserName);    p.add(new JLabel("Password: "));    p.add(tfPassword);    if (JOptionPane.showConfirmDialog(frame // may want to pass your application frame here                               ,p                               ,"Login"                               ,JOptionPane.OK_CANCEL_OPTION                               ,JOptionPane.PLAIN_MESSAGE                                ) == JOptionPane.OK_OPTION) {      System.out.println("User Name:"+tfUserName.getText());      System.out.println("Password:" + new String(tfPassword.getPassword()));    }  }  public static void main(String[] args) {    LoginDialogDemo frame = new LoginDialogDemo();  }}