Listeners Supported by Swing Components - Java Tutorial 5.0 英文版

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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

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 JavaBeans^TM 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.

The following table lists Swing components and the specialized listeners they support, not including listeners supported by all Components, Containers, or JComponents. 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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