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Trail: Creating a GUI with JFC/Swing
Lesson: Writing Event Listeners

## Listeners Supported by Swing Components

> You can tell what kinds of events a component can fire by looking at the kinds of event listeners you can register on it. For example, the `JComboBox` class defines these listener registration methods:
> - `addActionListener`
> - `addItemListener`
> - `addPopupMenuListener`
> Thus, a combo box supports action, item, and popup menu listeners in addition to the listener methods it inherits from `JComponent`.

> A component fires only those events for which listeners have registered on it. For example, if an action listener is registered on a particular combo box, but the combo box has no other listeners, then the combo box will fire only action events — no item or popup menu events.

> Listeners supported by Swing components fall into two categories:

> - Listeners that All Swing Components Support
> - Other Listeners that Swing Components Support

### Listeners that All Swing Components Support

> Because all Swing components descend from the AWT `Component` class, you can register the following listeners on any Swing component:
> component listener
>   Listens for changes in the component's size, position, or visibility.
> focus listener
>   Listens for whether the component gained or lost the ability to receive keyboard input.
> key listener
>   Listens for key presses; key events are fired only by the component that has the current keyboard focus.
> mouse listener
>   Listens for mouse clicks and mouse movement into or out of the component's drawing area.
> mouse-motion listener
>   Listens for changes in the cursor's position over the component.
> mouse-wheel listener (introduced in 1.4)
>   Listens for mouse wheel movement over the component.

> Two listener types introduced in release 1.3, `HierarchyListener` and `HierarchyBoundsListener`, listen to changes to a component's containment hierarchy. These listener types aren't useful to most programs and can generally be ignored.

> All Swing components descend from the AWT `Container` class, but many of them aren't used as containers. So, technically speaking, any Swing component can fire container events, which notify listeners that a component has been added to or removed from the container. Realistically speaking, however, only containers (such as panels and frames) and compound components (such as combo boxes) typically fire container events.

> `JComponent` provides support for three more listener types. You can register an ancestor listener to be notified when a component's containment ancestors are added to or removed from a container, hidden, made visible, or moved. This listener type is an implementation detail which predated hierarchy listeners and can generally be ignored.

> The other two listener types are part of the Swing components' conformance to the JavaBeansTM specification. Among other things, this means that Swing components support bound and constrained properties and notify listeners of changes to the properties. Property change listeners listen for changes to bound properties and are used by several Swing components, such as formatted text fields, to track changes on a component's bound properties. Also, property change listeners, as well as vetoable change listeners are used by builder tools to listen for changes on constrained properties. For more information refer to the Properties lesson in the JavaBeans trail.

### Other Listeners that Swing Components Support

> The following table lists Swing components and the specialized listeners they support, not including listeners supported by all `Component`s, `Container`s, or `JComponent`s. In many cases, the events are fired directly from the component. In other cases, the events are fired from the component's data or selection model. To find out the details for the particular component and listener you're interested in, go first to the component how-to section, and then if necessary to the listener how-to section.

> Component | Listener
> action | caret | change | document, undoable edit | item | list selection | window | other
> button |  |  |  |  |  |  |  |
> check box |  |  |  |  |  |  |  |
> color chooser |  |  |  |  |  |  |  |
> combo box |  |  |  |  |  |  |  |
> dialog |  |  |  |  |  |  |  |
> editor pane |  |  |  |  |  |  |  | hyperlink
> file chooser |  |  |  |  |  |  |  |
> formatted text field |  |  |  |  |  |  |  |
> frame |  |  |  |  |  |  |  |
> internal frame |  |  |  |  |  |  |  | internal frame
> list |  |  |  |  |  |  |  | list data
> menu |  |  |  |  |  |  |  | menu
> menu item |  |  |  |  |  |  |  | menu key menu drag mouse
> option pane |  |  |  |  |  |  |  |
> password field |  |  |  |  |  |  |  |
> popup menu |  |  |  |  |  |  |  | popup menu
> progress bar |  |  |  |  |  |  |  |
> radio button |  |  |  |  |  |  |  |
> slider |  |  |  |  |  |  |  |
> spinner |  |  |  |  |  |  |  |
> tabbed pane |  |  |  |  |  |  |  |
> table |  |  |  |  |  |  |  | table model table column model cell editor
> text area |  |  |  |  |  |  |  |
> text field |  |  |  |  |  |  |  |
> text pane |  |  |  |  |  |  |  | hyperlink
> toggle button |  |  |  |  |  |  |  |
> tree |  |  |  |  |  |  |  | tree expansion tree will expand tree model tree selection
> viewport (used by scrollpane) |  |  |  |  |  |  |  |

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