How can I change the width of a JComboBox dropdown list?

Question

I have an editable JComboBox which contains a list of single letter values. Because of that the combobox is very small.

Every letter has a special mean

Answer 1

Sounds like you'll need to write your own ComboBoxUI.

There is a good example here that shows how to accomplish this.

Also note, the method you would probably be interested in is the createPopup() method. This is the method that creates the popup for the combo box and where you would be able to customize it.