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How to Write an Item Listener

Item events are fired by components that implement the ItemSelectable interface. Generally, ItemSelectable components maintain on/off state for one or more items. The Swing components that fire item events include check boxes, check box menu items, and combo boxes.

Here is some item-event handling code taken from ComponentEventDemo.java:

//where initialization occurs
checkbox.addItemListener(this);
...
public void itemStateChanged(ItemEvent e) {
    if (e.getStateChange() == ItemEvent.SELECTED) {
        label.setVisible(true);
        ...
    } else {
        label.setVisible(false);
    }
}

The Item Listener API

The ItemListener Interface

Because ItemListener has only one method, it has no corresponding adapter class.

Method	Purpose
itemStateChanged(ItemEvent)	Called just after a state change in the listened-to component.

The ItemEvent Class

Method	Purpose
Object getItem()	Returns the component-specific object associated with the item whose state changed. Often this is a String containing the text on the selected item.
ItemSelectable getItemSelectable()	Returns the component that fired the item event. You can use this instead of the getSource method.
int getStateChange()	Returns the new state of the item. The ItemEvent class defines two states: SELECTED and DESELECTED.

The following table lists some examples that use item listeners.

Example	Where Described	Notes
ComponentEventDemo	This section and How to Write a Component Listener	Listens for item events on a check box, which determines whether a lable is visible.
CheckBoxDemo	How to Use Check Boxes	Four check boxes share one item listener, which uses getItemSelected to determine which check box fired the event.
MenuDemo	How to Use Menus	Listens for item events on a check box menu item.
MenuDemo	How to Use Scroll Panes	Listens for item events on a toggle button.

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