Problem with layout and changing content

Question

Hi, I`m new to Swing and I have a problem with layout.
I want to make a menu using JButtons so that depending on which button you click you`ll get different content in the window. And first of all I don`t know how to center the buttons.
I have a JFrame called GameWindow that has a JPanel field called content. My idea was to create a JPanel with buttons and then using ActionListeners change the JPanel held in 'content'.
Here`s the code:
public class GameWindow extends JFrame{     
     private static final long serialVersionUID = 1L;
     private JPanel content;
     private Player player;
     public GameWindow(){          
          super("Dawn Crystal");
          Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
          setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
          setSize((int)screenSize.getWidth(), (int)screenSize.getHeight());
          setExtendedState(MAXIMIZED_BOTH);
     public void mainMenu(){
          content = new MainMenu(this);
          Dimension dim = content.getSize();
          setLayout(null);                    
          Dimension screen = Toolkit.getDefaultToolkit().getScreenSize();
          int x = (int)((screen.getWidth() - dim.getWidth()) / 2);
          int y = (int)((screen.getHeight() - dim.getHeight()) / 2);
          int dimX = (int)dim.getWidth();
          int dimY = (int)dim.getHeight();          
          content.setBounds(x, y, 120, 120);          
          getContentPane().add(content);          
          setVisible(true);
     public void adventureScreen(){
          //so far empty
     public void createNewPlayer(){
          content.setVisible(false);
          content = new NewPlayerCreationWindow();
          getContentPane().add(content);          
          content.setVisible(true);
          //setVisible(true);
     public void setPlayer(Player p){ player=p; }
public class MainMenu extends JPanel{     
     private static final long serialVersionUID = 1L;     
     private JPanel mainMenuButtons;
     private JButton newGame;
     private JButton loadGame;
     private JButton options;
     private JButton exit;
     public MainMenu(GameWindow par){
          mainMenuButtons = new JPanel();     
          //create buttons
          newGame = new JButton("NEW GAME");
          loadGame = new JButton("LOAD GAME");
          options = new JButton("OPTIONS");
          exit = new JButton("EXIT");
          //create action listeners
          newGame.addActionListener(new NewGameListener());
          exit.addActionListener(new ExitListener(par));     
          //add buttons to panel
          mainMenuButtons.setLayout( new GridLayout(4,1));
          mainMenuButtons.add(newGame);
          mainMenuButtons.add(loadGame);
          mainMenuButtons.add(options);
          mainMenuButtons.add(exit);     
          add(mainMenuButtons);          
}When it displays the buttons are at the top of the frame rather than in the center - I thought that was how the default layout would behave. So that`s my first question - how to center it.
Secondly I have NewPlayerCreationWindow written but when I call createNewPlayer() I get an empty frame - what am I doing wrong?
Finally I`d like to ask how can I make the frame appear as maximized when the application is started? The setExtendedState(MAXIMIZED_BOTH); doesn`t help actually because the window`s height is too big and a part of window is hidden under the system bar. I want to have it maximized regardless of screen resolution.

Answer 1

Use a [url http://java.sun.com/docs/books/tutorial/uiswing/layout/visual.html]Card Layout.