Toggle Buttons - The Definitive Guide to Java Swing - page 138

Listening to JRadioButton Events with an ItemListener
Depending on what you're trying to do, using an ItemListener with a JRadioButton is usually
not the desired event-listening approach. When an ItemListener is registered, a new JRadioButton
selection notifies the listener twice: once for deselecting the old value and once for selecting
the new value. For reselections (selecting the same choice again), the listener is notified only once.
To demonstrate, the following listener will detect reselections, as the ActionListener did
earlier, and will report the selected (or deselected) element.
ItemListener itemListener = new ItemListener() {
String lastSelected;
public void itemStateChanged(ItemEvent itemEvent) {
AbstractButton aButton = (AbstractButton)itemEvent.getSource();
int state = itemEvent.getStateChange();
String label = aButton.getText();
String msgStart;
if (state == ItemEvent.SELECTED) {
if (label.equals(lastSelected)) {
msgStart = "Reselected -> ";
} else {
msgStart = "Selected -> ";
}
lastSelected = label;
} else {
msgStart = "Deselected -> ";
}
System.out.println(msgStart + label);
}
};
To work properly, some new methods will be needed for RadioButtonUtils to enable you
to attach the ItemListener to each JRadioButton in the ButtonGroup . They're listed in the
following section with the source for the complete example.
Listening to JRadioButton Events with a ChangeListener
The ChangeListener responds to the JRadioButton just as it does with the JToggleButton and
JCheckBox . A subscribed listener is notified when the selected radio button is armed, pressed,
selected, or released and for various other properties of the button model. The only difference
with JRadioButton is that the ChangeListener is also notified of the state changes of the radio
button being deselected. The ChangeListener from the earlier examples could be attached to
the JRadioButton as well. It will just be notified more frequently.
The sample program shown in Listing 5-7 demonstrates all the listeners registered to the
events of two different JRadioButton objects. In addition, a JButton reports on the selected
elements of one of the radio buttons. Figure 5-12 shows the main window of the program.