JTabbedPane "border bug" Windows LAF

Question

I noticed something similar to a bug when using JTabbedPane in Windows Look And Feel (on Windows 10).

The tabbed pane has a grey extra border on the right (2 pixels) and on the left (1 pixel). That border is not visible if the tabbed pane is inside a JPanelwith the default background color (rgb: 240, 240, 240), but it shows up in a panel with a different background color (look screenshot below).

I also want to remove the 3 pixels white border under the tabs.

The only similar question i found on SO is this one: JTabbedPane in Windows L&F with unremovable border, but there isn't a solution which actually works (see code below).

In fact, changing TabbedPane.contentBorderInsetscould easily remove the white border below the tabs (by setting insets.top = -1), but it breaks the UI when trying to remove the right border.

I tried different solutions, both using UIManager.opaque and UIManager.background and by manually overriding isOpaque () and getBackground () methods, i also tried to set a null Border, without any positive result.

I think i found a kind of hack which should work on Windows 10, overriding getBorder () method in order to return a MatteBorder with the same extra border dimension and the parent background as border color. Also, to remove the top border under the tabs i'm using:

setBackground ((Color) UIManager.get ("TabbedPane.highlight"));

for the panels inside the tabs.

This is a screnshot (code at the end of the post) which shows some tries i did, the last one is the result which i expected to have:

Is there any better solution to remove that nasty border? I'm afraid the UI could break down on different LAFs with the code i'm using right now ...

Should i create a factory method to check if the current LAF is "Windows", something like:

if (UIManager.getLookAndFeel ().getName ().equals ("Windows") {
    // Create "Custom" JTabbedPane, ovveriding getBorder method and setting panel background ...
}
else {
    // Create default JTabbedPane ...
}

Thanks in advance, here there is the code i used:

import java.awt.*;
import javax.swing.*;
import javax.swing.border.*;
public class TabbedPaneTest
{
    public static void main (String [] a) {
        SwingUtilities.invokeLater (new Runnable () {
            @Override public void run () {
                try {
                    UIManager.put ("TabbedPane.focus", new Color (0, 0, 0, 0));
                    UIManager.setLookAndFeel (UIManager.getSystemLookAndFeelClassName ());
                    createAndShowGUI ();
                }
                catch (Exception e) {
                    e.printStackTrace ();
                }
            }
        });
    }
    private static void createAndShowGUI () {
        JFrame frame = new JFrame ("Tabbed Pane Test");
        frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
        frame.setContentPane (new MainPanel ());
        frame.pack ();
        frame.setLocationRelativeTo (null);
        frame.setVisible (true);
    }
}
class MainPanel extends JPanel
{
    public MainPanel () {
        String [] labels = {"Default", "Panel background", "Content border insets", "Content opaque", "Matte border/Panel background"};
        Color [] backgrounds = {(Color) UIManager.get ("Panel.background"), Color.WHITE, Color.BLACK, Color.RED};
        setLayout (new GridLayout (backgrounds.length + 1, labels.length, 20, 10));
        for (int i = 0; i < labels.length; i ++) add (new JLabel (labels [i], JLabel.CENTER));
        for (int i = 0; i < backgrounds.length; i ++) {
            for (int j = 0; j < labels.length; j++) {
                JPanel panel = new JPanel (new FlowLayout (FlowLayout.CENTER, 20, 10));
                panel.add (createTabbedPane (j + 1));
                panel.setBackground (backgrounds [i]);
                add (panel);
            }
        }
        setBorder (new EmptyBorder (5, 5, 5, 5));
    }
    private JTabbedPane createTabbedPane (int i) {
        JTabbedPane tabbedPane;
        if (i == 3) {
            Insets oldValue = (Insets) UIManager.get ("TabbedPane.contentBorderInsets");
            UIManager.put ("TabbedPane.contentBorderInsets", new Insets (-1, 2, 2, 2));
            tabbedPane = new JTabbedPane ();
            UIManager.put ("TabbedPane.contentBorderInsets", oldValue);
        }
        else if (i == 4) {
            UIManager.put ("TabbedPane.contentOpaque", false);
            tabbedPane = new JTabbedPane ();
            UIManager.put ("TabbedPane.contentOpaque", true);
        }
        else if (i == 5) {
            tabbedPane = new JTabbedPane () {
                @Override public Border getBorder () {
                    Container parent = getParent ();
                    if (parent == null) return super.getBorder ();
                    return new MatteBorder (0, 0, 1, 2, parent.getBackground ());
                }
            };
        }
        else tabbedPane = new JTabbedPane ();
        JPanel panel1 = new JPanel (new FlowLayout (FlowLayout.LEFT, 80, 50));
        JPanel panel2 = new JPanel (new FlowLayout (FlowLayout.LEFT, 80, 50));
        if (i == 2 || i == 5) {
            Color highlightColor = (Color) UIManager.get ("TabbedPane.highlight");
            panel1.setBackground (highlightColor);
            panel2.setBackground (highlightColor);
        }
        tabbedPane.add ("Tab 1", panel1);
        tabbedPane.add ("Tab 2", panel2);
        return tabbedPane;
    }
}