Java 将JPanel对象添加到单独的JPanel中

我正在处理一个菜单，我想使它尽可能面向对象，所以我为菜单JPanel对象创建了一个单独的类。问题是它不想将它添加到我的主JPanel中。我做错了什么？我应该如何修复它

主类：

package StackOverflow;
import java.awt.CardLayout;
import javax.swing.*;

public class Main {

    private JFrame frame = new JFrame();
    private JPanel MainPanel = new JPanel();
    private CardLayout cl = new CardLayout();
    private GamePanel gp = new GamePanel();

    public Main(){
        frame.setLocation(100, 100);
        frame.setSize(1200, 700);
        frame.setTitle("Rain | Pre-Alpha");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        MainPanel.setLayout(cl);

        MainPanel.add(gp, "1");

        frame.add(MainPanel);

        cl.show(MainPanel, "1");

        frame.setVisible(true);
    }

    public static void main(String[] args) {
        new Main();
    }
}    

package StackOverflow;
import java.awt.Color;
import javax.swing.JPanel;

public class GamePanel {
    private JPanel GamePanel = new JPanel();

    public GamePanel(){
        GamePanel.setBackground(Color.green);
    }
}

游戏面板类：

package StackOverflow;
import java.awt.CardLayout;
import javax.swing.*;

public class Main {

    private JFrame frame = new JFrame();
    private JPanel MainPanel = new JPanel();
    private CardLayout cl = new CardLayout();
    private GamePanel gp = new GamePanel();

    public Main(){
        frame.setLocation(100, 100);
        frame.setSize(1200, 700);
        frame.setTitle("Rain | Pre-Alpha");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        MainPanel.setLayout(cl);

        MainPanel.add(gp, "1");

        frame.add(MainPanel);

        cl.show(MainPanel, "1");

        frame.setVisible(true);
    }

    public static void main(String[] args) {
        new Main();
    }
}    

package StackOverflow;
import java.awt.Color;
import javax.swing.JPanel;

public class GamePanel {
    private JPanel GamePanel = new JPanel();

    public GamePanel(){
        GamePanel.setBackground(Color.green);
    }
}

---

无法将类添加到

JFrame

，JFrame接受

组件

：

public Component add(Component comp, int index)

所以你有很多方法来解决你的问题：

选择1 改为扩展

JPanel

：

public class GamePanel extends JPanel {

    public GamePanel() {
        super.setBackground(Color.green);
    }
}

选择2 您可以使用getter和setter：

public class GamePanel {

    private JPanel GamePanel = new JPanel();

    public JPanel getGamePanel() {
        return GamePanel;
    }

    public void setGamePanel(JPanel GamePanel) {
        this.GamePanel = GamePanel;
    }

    public GamePanel() {
        GamePanel.setBackground(Color.green);
    }

}

您可以这样添加您的JPanel：

MainPanel.add(gp.getGamePanel(), "1");