Java CardLayout IllegalArgumentException

Question

我正在制作一个使用CardLayout在四个JPanels (gamePanel、startMenu、pauseMenu和levelMenu)之间切换的游戏。我得到了例外"java.lang.IllegalArgumentException: CardLayout的错误家长“。但是，我将所有的卡片添加到面板中，它有布局管理器CardLayout，所以我不明白为什么面板不是父版。我看过CardLayout的Java教程以及涉及IllegalArgumentException的堆栈溢出问题，但我看不出我做错了什么。提前谢谢。

游戏：

import java.awt.CardLayout;

import javax.swing.JFrame;
import javax.swing.JPanel;

/** Class Contains the main method and the game's logic */
public class Game {

    /** Field The JFrame for the game */
    public JFrame frame = new JFrame();

    /** Field The JPanel that uses CardLayout to only display one JPanel at a time */
    private JPanel panel;

    /** Field The CardLayout that controls which JPanel is showing */
    private CardLayout cardLayout;

    /** Field The JPanel that displays the playing field */
    private JPanel gamePanel = new JPanel();

    /** Field The first menu the player sees */
    private JPanel startMenu = new JPanel();

    /** Field The menu the player sees when the game is paused */
    private JPanel pauseMenu = new JPanel();

    /** Field The menu that allows the player to select which level to play */
    private JPanel levelMenu = new JPanel();

    /** Constructor for Game with no parameters */
    public Game() {
        initializeGame();
    }

    /** Main method of Game */
    public static void main(String argv[]) {
        new Game();
    }

    /** Sets up frame and panel */
    private void initializeGame() {
        panel = createPanel();

        panel = (JPanel) frame.getContentPane();

        cardLayout.show(panel, "startMenu");
    }

    private JPanel createPanel() {
        panel = new JPanel();
        cardLayout = new CardLayout();
        panel.setLayout(cardLayout);

        panel.add(startMenu, "startMenu");
        panel.add(pauseMenu, "pauseMenu");
        panel.add(levelMenu, "levelMenu");
        panel.add(gamePanel, "gamePanel");

        return panel;
    }

}

Answer 1

您已经将panel变量分配给两个对象，一个由createPanel()方法创建，另一个通过获取contentPane。一个是向GUI添加组件，另一个是调用show方法，由于这个原因，JVM会抱怨。解决方案不是这样做，只给这个变量分配一次对象。

为了明白我的意思，搜索你的代码

 panel = 

看到突然出现的台词。