I need to make the date parts (dd, MMMM, yyyy) to be vertically aligned. I asked a question at Fixed length of month and day in date format? to insert padding letters, but I
As suggested by @mKorbel, a suitable TableCellRenderer is the right choice, but you may have to override paintComponent() and render the text using the graphics context's FontMetrics as shown here.
If numeric months are acceptable, most proportionally-spaced fonts give digit glyphs the same constant advance.