JLabel Right-Justified Icon and Text

Perhaps this would be more what you're looking for? It should align everything on the right side of the panel (more so than the example you were looking at):

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

public class TempProject
{
    public static void main(String args[])
    {
        EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                Box mainContent = Box.createVerticalBox();
                mainContent.add(TempProject.getLabel("abc"));
                mainContent.add(TempProject.getLabel("Longer"));
                mainContent.add(TempProject.getLabel("Longerest"));
                mainContent.add(TempProject.getLabel("Smaller"));

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

    public static JLabel getLabel(String text){
        JLabel c = new JLabel(text);
        c.setHorizontalTextPosition(SwingConstants.LEADING);
        c.setAlignmentX(SwingConstants.RIGHT);
        c.setIcon(UIManager.getIcon("FileChooser.detailsViewIcon"));
        return c;
    }
}

The example cited uses layout and label properties for right/left justification.

Additionally, consider implementing the Icon interface in a JList renderer, where setHorizontalAlignment() and setVerticalAlignment() may be used to control the relative geometry. This related TableCellRenderer illustrates the principle.