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Trail: Creating a GUI with JFC/Swing
Lesson: Writing Event Listeners
Section: Implementing Listeners for Commonly Handled Events
Writing Event Listeners
Introduction to Event Listeners
General Information about Writing Event Listeners
Listeners Supported by Swing Components
Implementing Listeners for Commonly Handled Events
How to Write an Action Listener
How to Write a Caret Listener
How to Write a Change Listener
How to Write a Component Listener
How to Write a Container Listener
How to Write a Document Listener
How to Write a Focus Listener
How to Write an Internal Frame Listener
How to Write an Item Listener
How to Write a Key Listener
How to Write a List Data Listener
How to Write a List Selection Listener
How to Write a Mouse Listener
How to Write a Mouse-Motion Listener
How to Write a Mouse-Wheel Listener
How to Write a Property Change Listener
How to Write a Table Model Listener
How to Write a Tree Expansion Listener
How to Write a Tree Model Listener
How to Write a Tree Selection Listener
How to Write a Tree-Will-Expand Listener
How to Write an Undoable Edit Listener
How to Write Window Listeners
Listener API Table
Solving Common Event-Handling Problems
Home Page > Creating a GUI with JFC/Swing > Writing Event Listeners
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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`.

### Examples that Use Item Listeners

> 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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