I have an application that has nested JTabbedPanes. Each of the JTabbedPanes include other JTabbedPanes.

I want to check something before allowing the user to leave the current tab.

When you run the code below, you'll see that the Months->February tab has an ALLOW checkbox.

If the ALLOW checkbox is selected, then I want to allow the user navigate to leave the current panel. If it is not, then they can't leave until it is.

I can't seem to find a way to handle the request to leave BEFORE the next Component (which may be on another JTabbedPane) is shown.

This can be demonstrated by going to the Months->February tab, and then selecting the Colors Tab.

Any ideas?

```
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.event.HierarchyEvent;
import java.awt.event.HierarchyListener;

import javax.swing.JCheckBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTabbedPane;
import javax.swing.SwingUtilities;

public class VerifyBeforeLeavingTab extends JFrame
{
    private static final long   serialVersionUID    = 1L;

    public VerifyBeforeLeavingTab()
    {
        setSize(700, 700);

        JTabbedPane mainTabbedPane = new JTabbedPane(JTabbedPane.TOP);

        MyJTabbedPane colorsPane = new MyJTabbedPane(JTabbedPane.TOP, "colors");
        JPanel bluePanel = new JPanel();
        bluePanel.setBackground(Color.blue);
        colorsPane.addTab("Blue", bluePanel);

        JPanel redPanel = new JPanel();
        redPanel.setBackground(Color.red);
        colorsPane.addTab("Red", redPanel);

        mainTabbedPane.addTab("Colors", colorsPane);

        JTabbedPane monthsPane = new MyJTabbedPane(JTabbedPane.TOP, "months");

        JPanel janPanel = new JPanel();
        monthsPane.addTab("January", janPanel);

        JPanel febPanel = new MyUnleavableJPanel();
        monthsPane.addTab("February", febPanel);

        mainTabbedPane.addTab("Months", monthsPane);

        add(mainTabbedPane, BorderLayout.CENTER);

        getContentPane().add(mainTabbedPane);
    }

    private class MyUnleavableJPanel extends JPanel
    {
        private static final long   serialVersionUID    = 1L;

        public MyUnleavableJPanel()
        {
            final JCheckBox chckBoxAllowToLeave = new JCheckBox("Allow to leave");
            chckBoxAllowToLeave.setBounds(100, 100, 50, 50);
            this.add(chckBoxAllowToLeave);

            addHierarchyListener(new HierarchyListener()
            {
                public void hierarchyChanged(HierarchyEvent e)
                {
                    if ((HierarchyEvent.SHOWING_CHANGED & e.getChangeFlags()) != 0)
                    {
                        if (isShowing())
                        {
                            System.out.println("Showing an unleavable panel");
                        }
                        else
                        {
                            // TODO: Do not let them leave this JCheckbox is selected
                            if (chckBoxAllowToLeave.isSelected())
                            {
                                System.out.println("OK to leave");
                            }
                            else
                            {
                                System.out.println("Not allowed to leave");
                            }
                        }
                    }
                }
            });
        }
    }

    private class MyJTabbedPane extends JTabbedPane
    {
        private static final long   serialVersionUID    = 1L;

        public MyJTabbedPane(int i, String name)
        {
            super(i);
            setName(name);
        }

        @Override
        public void setSelectedIndex(int index)
        {
            System.out.println("Now on '" + getName() + "' tab #" + index);
            super.setSelectedIndex(index);
        }
    }

    private static void createAndShowGUI()
    {
        // Create and set up the window.
        VerifyBeforeLeavingTab frame = new VerifyBeforeLeavingTab();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }

    public static void main(String[] args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                try
                {
                    createAndShowGUI();
                }
                catch (Exception e)
                {
                    e.printStackTrace();
                    System.exit(0);
                }
            }
        });
    }

}

```