More Swing components - An Introduction to Graphical User Interfaces with Java Swing - page 174

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Changes in the list model (additions or deletions of entries) are automatically

displayed by the corresponding list. No call to repaint is necessary.

16.2.4 List listeners and list events

As specified above, our application has to react to a list entry being selected. The
appropriate listener for this purpose is a ListSelectionListener .Itisassigned
to a JList , say myjlist ,by

myjlist.addListSelectionListener(listener)

Interface ListSelectionListener requires the implementation of only one
method:

public void valueChanged(ListSelectionEvent evt)

This method is automatically called by the runtime system every time the selection

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is changed. It is not executed if the selection is unchanged, for example if the user
clicks in an item that is already selected. The body of this method has to contain
the code that should be executed in response to the selection.
Method valueChanged receives an object of type ListSelectionEvent as an
argument. This is automatically generated by the runtime system and contains
further information on the selection event that has occurred. We shall use the
following methods of ListSelectionEvent :

int getFirstIndex()
int getLastIndex()
boolean getIsAdjusting()

getFirstIndex() returns the position of the first (top-most) entry, the selection
mode of which might have changed (from selected to non-selected or vice
versa). 'Might' refers to the fact that the section state might be the same as
before. For example if entries 5 to 8 were selected and the user now selects 5 to
10 then the first selected index remains unchanged. Which entries are selected
can be found by using method getSelectedIndices of class JList .
getLastIndex() returns the position of the last (bottom-most) entry, the selection
mode of which might have changed. See also getFirstIndex() .
getIsAdjusting - changing the selection in a list triggers a series of actions, each

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of which generates a list selection event. For example previously selected en-
tries become unselected before new ones become selected. Usually, one would
prefer this series of events to be completed before the application reacts to the
change. For such a rapid series of events all but the last one return true as a
result of getIsAdjusting . Only the last one returns false as a result of getI-
sAdjusting . This can be used to wait for the end of the series of adjustments
before taking further action.

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At the moment, ListSelectionEvent supports only the selection modes SIN-

GLE_SELECTION and SINGLE_INTERVAL_SELECTION .