在Glasspane前显示InternalFrame

import javax.swing.*;

public class MainFrame extends JFrame {
    private JDesktopPane desktopPane;

    public MainFrame() {
        // 创建主窗口
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(800, 600);

        // 创建JDesktopPane对象
        desktopPane = new JDesktopPane();

        // 创建JInternalFrame对象
        JInternalFrame internalFrame = new JInternalFrame("Internal Frame", true, true, true, true);
        internalFrame.setSize(200, 200);
        internalFrame.setVisible(true);

        // 将JInternalFrame对象添加到JDesktopPane对象中
        desktopPane.add(internalFrame);

        // 将JDesktopPane对象添加到主窗口中
        setContentPane(desktopPane);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> {
            MainFrame frame = new MainFrame();
            frame.setVisible(true);
        });
    }
}