How to build a java Main Menu

Question

Obviously I am trying to make a main menu using the swing components. I understand that in order to make my menu happen, I have to utilize CardLayout, which I do in the code below:

(Everything is imported of course)

 public class Screen extends JFrame implements ActionListener {
private static final long serialVersionUID = 1L;

int width, height;

JButton play = new JButton("play");
JButton settings = new JButton("settings");
JButton exit = new JButton("exit");
JButton mainMenu = new JButton("main menu");

CardLayout layout = new CardLayout();

JPanel panel = new JPanel();
JPanel game = new JPanel();
JPanel menu = new JPanel(); 

public Screen(int width, int height) {
    this.width = width;
    this.height = height;

    panel.setLayout(layout);        
    addButtons();

    setSize(width, height);
    setResizable(false);
    setLocationRelativeTo(null);
    setVisible(true);
    setTitle("BUILD YOUR EMPIRE");
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    requestFocus();

}

private void addButtons() {

    play.addActionListener(this);
    settings.addActionListener(this);
    exit.addActionListener(this);
    mainMenu.addActionListener(this);

    //menu buttons
    menu.add(play);
    menu.add(settings);
    menu.add(exit);

    //game buttons
    game.add(mainMenu);

    //background colors
    game.setBackground(Color.MAGENTA);
    menu.setBackground(Color.GREEN);

    //adding children to parent Panel
    panel.add(menu,"Menu");
    panel.add(game,"Game");

    add(panel);
    layout.show(panel,"Menu");

}

public void actionPerformed(ActionEvent event) {

    Object source = event.getSource();

    if (source == exit) {
        System.exit(0);
    } else if (source == play) {
        layout.show(panel, "Game");
    } else if (source == settings){

    } else if (source == mainMenu){
        layout.show(panel, "Menu");
    }

    }
}

But when I run it, only the exit button works. When I hit the settings button nothing happens (as expected) but when I hit play button it crashes and gives me this error:

 Exception in thread "main" java.lang.IllegalArgumentException: wrong parent for CardLayout
at java.awt.CardLayout.checkLayout(Unknown Source)
at java.awt.CardLayout.show(Unknown Source)
at Screen.Buttons(Screen.java:69)
at Screen.<init>(Screen.java:31)
at Window.main(Window.java:29)

I dont understand what I am doing wrong. Any help on this will be greately appreciated thanks in advance.

Answer 1

Found it!

It was a matter of wrong order:

Buttons();
panel.setLayout(layout);        
layout.addLayoutComponent(panel, "Menu");

is wrong because you obviously need to set up the CardLayout in the panel before doing anything (like show) with it. So:

panel.setLayout(layout);        
layout.addLayoutComponent(panel, "Menu");
Buttons();

Although I don't know why do you need the line:

layout.addLayoutComponent(panel, "Menu");

looking at the tutorial it does not mention the necessity to use it.

Also method names should start in lower case, I was confused for a moment thinking that Buttons was a class. And you should use more descriptive names:

addButtons() instead of Buttons()

gamePanel instead of game

and so on.

Good job providing (not very extensive) relevant code, next time you should try adding a main also so we can just execute and test it :)