Notice that the JComboBox is created as a single unit. An array of Objects is passed to the constructor, or, Objects are added one at a time later on. The items in a JComboBox don't have to be Strings, they can be anything that is drawable.
JComboBox generates ItemEvents. When a new selection overrides a previous selection, two events are broadcast. It is up to the programmer to distinguish between ItemEvent.SELECTED events and ItemEvent.DESELECTED events.
[Reference: Topley, pp611-622]