Is there a way to center only the selected item in a JComboBox (so keep all items in the combo box left-aligned)

Question

I know there is a simple way to center all the items in the JComboBox, but i have searched StackOverflow and across the web and there is no talk about how to center the selected item only.

To make it clear, when I select an item from the combo box, this box closes the list and shows the selected item only. It is this item I want centered.

Is there a way to do it?

Answer 1

This is controlled by the renderer.

The selected item is renderered when the index passed to the renderer is -1.

You can create a custom renderer and change the alignment of the text based on the index:

import java.awt.Component;
import javax.swing.*;
import javax.swing.plaf.basic.BasicComboBoxRenderer;

public class ComboRenderer
{
   public void makeUI()
   {
      JComboBox<String> comboBox = new JComboBox<>(new String[]{"A", "B", "C"});

      comboBox.setRenderer(new BasicComboBoxRenderer()
      {
         @Override
         public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus)
         {
            super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);

            setHorizontalAlignment( index == -1 ? JLabel.CENTER : JLabel.LEFT );

            return this;
         }
      });

      JFrame frame = new JFrame();
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.add(comboBox);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args)
   {
      SwingUtilities.invokeLater(() -> new ComboRenderer().makeUI() );
   }
}