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 buttons like check boxes, check menu items, toggle buttons etc...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.

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

The ItemEvent Class

MethodPurpose
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 .

Examples that Use Item Listeners

The following table lists some examples that use item listeners.

ExampleWhere DescribedNotes
ComponentEventDemoThis section and How to Write a Component ListenerListens for item events on a check box, which determines whether a lable is visible.
CheckBoxDemoHow to Use Check BoxesFour check boxes share one item listener, which uses getItemSelected to determine which check box fired the event.
MenuDemoHow to Use MenusListens for item events on a check box menu item.
MenuDemoHow to Use Scroll PanesListens for item events on a toggle button.