Switching JPanels

Question

So I'm trying to make a basic program to learn more about java, and I'm having trouble switching screens. I wanted to have a display class that I could call in other classes to handle all the panels and such, and then make a class to build each panel. What I'm trying to do at the moment is use a button in my startmenu class to change from one panel to another using a method in the display class.

Here's the code in the startmenu class:

public void actionPerformed(ActionEvent e)
{
 display.switchPanel("Start");
}

And here is my display class:

public class Display 
{
 JFrame frame;
 StartMenu start = new StartMenu();
 MainMenu main = new MainMenu();
 JPanel panel = new JPanel();
 JPanel startPanel = start.createPanel();
 JPanel mainPanel = main.createPanel();
 CardLayout card = new CardLayout();
 BorderLayout border = new BorderLayout();
 public void createDisplay()
 {
 frame = new JFrame("Insert Name");
 frame.setPreferredSize(new Dimension(800,600));
 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 frame.getContentPane().add(panel, BorderLayout.CENTER);
 panel.setLayout(border);
 panel.add(startPanel);
 panel.add(mainPanel);
 mainPanel.setVisible(false);
 startPanel.setVisible(true);
 frame.add(panel);
 frame.pack();
 frame.setVisible(true);
 frame.setResizable(false);
 }
 public void switchPanel(String x)
 {
 String p = x;
 if(p.equals("Start"))
 {
 mainPanel.setVisible(true);
 startPanel.setVisible(false);
 }
 }
}

• ControlAltDel: Check out CardLayout: docs.oracle.com/javase/7/docs/api/java/awt/CardLayout.html
• MadProgrammer: With you're current approach, you're going to have no end of issues battling with the BorderLayout, as it will only manage a single component at any one of it's 5 available positions. Instead, you should be making using of a CardLayout, it's what it's designed for. See How to Use CardLayout for more details
• Rwarfield: I was using cardlayout before, I have it set before the createDisplay method. When I tried to use .show though, it kept giving me an error in the method I call in the startmenu class
• Rwarfield: @MadProgrammer This is my previous code using cardlayout. ' public void switchPanel(String x) { String p = x; if(p.equals("Start")) { card.show(panel, "2"); } }' 'panel.setLayout(card); panel.add(startPanel, "1"); panel.add(mainPanel, "2");'

Answer 1

Use a CardLayout, it's what it's designed for, for example...

public class Display {
 public static final String START_VIEW = "start";
 public static final String MAIN_VIEW = "main";
 JFrame frame;
 StartMenu start = new StartMenu();
 MainMenu main = new MainMenu();
 JPanel panel = new JPanel();
 JPanel startPanel = start.createPanel();
 JPanel mainPanel = main.createPanel();
 CardLayout card = new CardLayout();
 public void createDisplay() {
 frame = new JFrame("Insert Name");
 frame.setPreferredSize(new Dimension(800, 600));
 frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 frame.getContentPane().add(panel, BorderLayout.CENTER);
 panel.setLayout(card);
 panel.add(startPanel, START_VIEW);
 panel.add(mainPanel, MAIN_VIEW);
 mainPanel.setVisible(false);
 startPanel.setVisible(true);
 frame.add(panel);
 frame.pack();
 frame.setVisible(true);
 frame.setResizable(false);
 }
 public void switchPanel(String x) {
 card.show(panel, x);
 }
}

Then you might use something like...

public void actionPerformed(ActionEvent e)
{
 display.switchPanel(Display.START_VIEW);
}

to switch between the views

See How to Use CardLayout for more details

• Rwarfield: Cool, this helped me understand how to implement cardlayout better! Thanks! I tried that and still got the same error though...maybe I added action listener to my button wrong? I did this startBtn.addActionListener(this); The error is : Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
• MadProgrammer: Then I assume that display is null
• Rwarfield: I did private Display display; at the start of the startmenu class, is that the incorrect way to access that class in another class?
• MadProgrammer: In this yes, you need a reference to the instance of Display which is actually showing all the stuff on the screen