The JComboBox should act like a button when it is not editable. Meaning, rollover on any part of the combo should cause the entire combo box to go into rollover state. Also, pressing on any part of the combo should cause a combo box dropdown to appear, and the combo box should go into it's pressed state. For backwards compatibility, a UI default key should be used to indicate whether the combo should "act like a button" when not editable.