Both the focusGained and focusLost methods do not work for JPanel.

Code snippet:
import javax.swing.JToolBar;
import javax.swing.JButton;
import javax.swing.ImageIcon;

import javax.swing.JFrame;
import javax.swing.JTextArea;
import javax.swing.JScrollPane;
import javax.swing.JPanel;
import javax.swing.JTabbedPane;

import java.awt.*;
import java.awt.event.*;

public class ToolBarDemo extends JFrame implements FocusListener {

    public ToolBarDemo() {
        //Do frame stuff.
        super("ToolBarDemo");
        addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });

        //Create the toolbar.
        //JToolBar toolBar = new JToolBar();
        //toolBar.addFocusListener(this);
        
        //Lay out the content pane.
        JPanel contentPane = new JPanel();
        contentPane.addFocusListener(this);
        contentPane.setLayout(new BorderLayout());
        contentPane.setPreferredSize(new Dimension(400, 100));
        //contentPane.add(toolBar, BorderLayout.CENTER);
        setContentPane(contentPane);
    }
    
    public void focusGained(FocusEvent e) {
      System.out.println("focusGained: " + e.getComponent());
    }
    
    public void focusLost(FocusEvent e) {
      System.out.println("focusLost: " + e.getComponent());
    }
    
    public static void main(String[] args) {
        ToolBarDemo frame = new ToolBarDemo();
        frame.pack();
        frame.setVisible(true);
    }
}