The JComboBox Class
JComboBox combines a button or editable field and a drop-down list.
It is very similar to the AWT Choice
component and even implements the ItemSelectable interface for backward
compatibility. By default, the JComboBox component provides a single text
edit field adjacent to a small button with a downward arrow. When the
button is pressed, a pop-up list of choices is displayed, one of which
can be selected by the user. If a selection is made, the choice is
copied into the edit field, and the pop up disappears. If there was a
previous selection, it is erased. You can also remove the pop up by
pressing Tab (or Esc, depending on the L&F) while the combo box has
the focus. Figure 7-11 shows
combo boxes as they appear in four different L&Fs.

Figure 7-11. The JComboBox component in four L&Fs
The text field in the JComboBox
component can be either editable or not editable. This state is controlled by the
editable property. If the text field
is editable, the user is allowed to type information into the text box
(which may not correspond to anything in the list), as well as make
selections from the list. If the component is not editable, the user can
only make selections from the list.
Unless you specify a set of objects in the constructor, the
combo box comes up empty. You can use the addItem( ) method to add objects to the combo box list. Conversely,
the removeItem( ...