我正在尝试理解如何使用FocusListener控制JInternalFrames

import javax.swing.*;
import java.awt.*;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;

public class InternalFrameExample extends JFrame {
    private JDesktopPane desktopPane;

    public InternalFrameExample() {
        setTitle("Internal Frame Example");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(400, 300);

        desktopPane = new JDesktopPane();
        setContentPane(desktopPane);

        JInternalFrame internalFrame1 = createInternalFrame("Internal Frame 1");
        JInternalFrame internalFrame2 = createInternalFrame("Internal Frame 2");

        desktopPane.add(internalFrame1);
        desktopPane.add(internalFrame2);

        setVisible(true);
    }

    private JInternalFrame createInternalFrame(String title) {
        JInternalFrame internalFrame = new JInternalFrame(title, true, true, true, true);
        internalFrame.setSize(200, 150);
        internalFrame.setLocation(50, 50);

        // 添加FocusListener
        internalFrame.addFocusListener(new FocusListener() {
            @Override
            public void focusGained(FocusEvent e) {
                // 组件获得焦点时的处理逻辑
                internalFrame.getContentPane().setBackground(Color.YELLOW);
            }

            @Override
            public void focusLost(FocusEvent e) {
                // 组件失去焦点时的处理逻辑
                internalFrame.getContentPane().setBackground(Color.WHITE);
            }
        });

        internalFrame.setVisible(true);
        return internalFrame;
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(InternalFrameExample::new);
    }
}