 <p>It may help to note that <code>comboPanel</code> is a <code>JPanel</code> having the default <code>FlowLayout</code>, which centers components based on the preferred sizes of the comboboxes. As a result, they "clump" together in the middle. Some alternatives:</p> <ul> <li><p>Specify a <code>GridLayout</code> having an extra column and use an empty component for the check column. The initial tableau will be aligned, although subsequent changes to the column widths will change that.</p> <pre><code>JPanel comboPanel = new JPanel(new GridLayout(0, annots.length + 1)); </code></pre></li> <li><p>Add a combobox to each relevant header using the approach shown <a href="http://stackoverflow.com/a/29963916/230513">here</a>, being mindful of the caveats adduced <a href="http://stackoverflow.com/a/7146216/230513">here</a>.</p></li> </ul>