List Model Controls - The Definitive Guide to Java Swing - page 485

■ Tip To programmatically deselect the current choice of a JComboBox , call setSelectedIndex() with an

argument of -1.

Listening to Keyboard Events with a KeySelectionManager
The JComboBox has a public inner interface that's fairly important. KeySelectionManager , and its
default implementation, manages selection from the keyboard of items within the JComboBox .
The default manager locates the next element that corresponds to the pressed key. It has
memory, so if you have entries that start with similar prefixes, users can continue typing until
there is enough of a match to be unique. If you don't like this behavior, you can either turn it
off or create a new key selection manager.

■ Note The KeySelectionManager works only in combo boxes that are not editable.

If you want to turn off the key-selection capabilities, you can't do so by simply setting the
keySelectionManager property to null . Instead, you must create an implementation of the
interface with an appropriate method. The single method of the interface is public int
selectionForKey(char aKey, ComboBoxModel aModel) . In the event the pressed key doesn't
match any elements, the routine needs to return -1. Otherwise, it should return the position of
the matched element. So, to ignore keyboard input, the routine should always return -1, as
shown here:

JComboBox.KeySelectionManager manager =
new JComboBox.KeySelectionManager() {
public int selectionForKey(char aKey, ComboBoxModel aModel) {
return -1;
}
};
aJcombo.setKeySelectionManager(manager);

Listening to JComboBox Events with an ActionListener
The primary means of listening for selection events is through an ActionListener , possibly set
with setAction(Action) . It will tell you when an element has been selected within a JComboBox .
Unfortunately, the listener doesn't know which element is selected.

■ Note Setting the ActionListener through setAction(Action) also configures the tooltip text and the
enabled state of the JComboBox based on the Action .