JComboBox on Windows 7 has rendering artifacts

Question

When I use a JComboBox on Windows 7, the four corners each have a pixel that doesn't match the background colour of the parent component.

In Windows 8 this problem doesn't happen (although that could be because in Windows 8, the JComboBox is rendered as a perfect rectangle). Nor does it happen on OS X.

What can I do to make the corner pixels let the background colour of the parent component through?

Here's an image showing the problem:

Here's a self-contained code example I'm using:

import com.sun.java.swing.plaf.windows.WindowsLookAndFeel;

import javax.swing.*;
import java.awt.*;

public class Main {

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                try {
                    UIManager.setLookAndFeel(new WindowsLookAndFeel());
                } catch (Exception e) {
                    e.printStackTrace();
                }

                JPanel contentPane = new JPanel();
                contentPane.setBackground(Color.WHITE);

                JComboBox<String> comboBox = new JComboBox<String>(new String[]{"One", "Two"});
                contentPane.add(comboBox);

                JFrame frame = new JFrame("JComboBox Test");
                frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
                frame.setContentPane(contentPane);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }
}

Answer 1

Try removing the border...

comboBox.setBorder(null);

The next choice would be to design a specialised look and feel delegate that achieved what you wanted on Windows...

For example...

public static class MyComboBoxUI extends WindowsComboBoxUI {

    @Override
    protected void installDefaults() {
        super.installDefaults();
        LookAndFeel.uninstallBorder(comboBox);
    }

    public static ComponentUI createUI(JComponent c) {
        return new MyComboBoxUI();
    }

}

And then install it using...

UIManager.put("ComboBoxUI", MyComboBoxUI.class.getName());

This will mean you won't need to remove the borders from every combo box you create

Or, you could simply override the default border property in the UIManager...

UIManager.put("ComboBox.border", new EmptyBorder(0, 0, 0, 0));

Either way, it will effect all combo boxes created after you apply it...