Why does my login panel resize?

Question

Hi,
This is probably a basic problem. So please bear with me.
I'm making an application and Applet, where the user needs to log in. I created a Frame, that scales to cover the whole screen.
     dimension = Toolkit.getDefaultToolkit().getScreenSize();
     setBounds (0, 0, dimension.width, dimension.height);After the Frame is created, I create a JPanel in it, where the user needs to enter username and password. And as users go, they will make errors, so I have to add functionality to check on
1. Are username and password filled in
2. Can username and password be used to authenticate
So I need to draw that JPanel a few times. And there it goes wrong. So my question is, can you help me with my JPanel.
   // Constructor
   public LogInPanel () {
      width = 450;
      height = 350;
      // Create error label and set its colour
      errorLabel = new JLabel ("Fill in both fields", SwingConstants.LEFT);
      errorLabel.setForeground(Color.RED);
      setLayout(new GridLayout (4, 2)); // 4 rows, 2 columns
      setUp();
   public void actionPerformed(ActionEvent event) {
          command = event.getActionCommand();
          if (OK.equals(command)) {
               //Process the user name and password.
               userName = userNameField.getText();
               password = passwordField.getPassword();
               isError = ((userName.length() == 0) || (password.length ==0));
          if (!isError) {
               // TODO: Authenticate with system
          else {
               // Error condition, either user name or error not filled in. Do setUp() again.
               setUp();
    private void setUp () {
        // Set the size and location of this panel
        setBounds (width, height, width, height);
         // User name label and text field
         add (unameLabel);
         add (userNameField);
         // Password label and text field
         add(passLabel);
         add(passwordField);
         // Create okButton and add it to the layout
         JComponent okButton = createButtonPanel();
         add(okButton);
         // An empty panel to fill up the empty spot after the button
         JPanel emptyPanel = new JPanel();
         emptyPanel.setBackground(Color.WHITE);
        if (isError) {
            add(errorLabel);
        setSize(dimension.width/3, dimension.height/3);
        setVisible (true);
    private JComponent createButtonPanel() {
        JPanel panel = new JPanel(new GridLayout(0,1));
        JButton okButton = new JButton("OK");
        okButton.setActionCommand(OK);
        okButton.addActionListener(this);
        panel.add(okButton);
        return panel;
    }When I run the code I get the following LoginPanel displayed
|Username: | "userNameField"       |
|Password: | "add(passwordField)"  |
|OKbutton  |emptyPanel             |
|Nothing yet                       |
------------------------------------And as I emulate a stupid user, I directly press the OK button. What happens now is that my LoginPanel moves up a few lines, and increases four times (2x in width, 2x in height), to something like:
|Username: | "userNameField"                                           |
|Password: | "add(passwordField)"                                      |
|OKbutton  |emptyPanel                                                 |
|No error message!                                                     |
|                                                                      |
|                                                                      |
|                                                                      |
|                                                                      |
|                                                                      |
------------------------------------------------------------------------And I can't find the reason for that behaviour. So hopefully you see it. And if so, do tell.
TIA,
Abel

Answer 1

without your code, I can't tell why you are having this behavior, however I can tell you that when I've done something like this, I've done it differently. For one, I don't recreate the JPanel but rather I show a JOptionPane.showMessage(....) error message over the panel, the erase the JPanel's fields and set focus where I want it after the JOptionPane has been dealt with. This is simpler than your current plan and thus less likely to blow-up.