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JavaTM 2 Platform Std. Ed. v1.4.2 |
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java.lang.Objectjava.awt.Component
java.awt.Button
This class creates a labeled button. The application can cause
some action to happen when the button is pushed. This image
depicts three views of a "Quit" button as it appears
under the Solaris operating system:
The first view shows the button as it appears normally. The second view shows the button when it has input focus. Its outline is darkened to let the user know that it is an active object. The third view shows the button when the user clicks the mouse over the button, and thus requests that an action be performed.
The gesture of clicking on a button with the mouse
is associated with one instance of ActionEvent,
which is sent out when the mouse is both pressed and released
over the button. If an application is interested in knowing
when the button has been pressed but not released, as a separate
gesture, it can specialize processMouseEvent,
or it can register itself as a listener for mouse events by
calling addMouseListener. Both of these methods are
defined by Component, the abstract superclass of
all components.
When a button is pressed and released, AWT sends an instance
of ActionEvent to the button, by calling
processEvent on the button. The button's
processEvent method receives all events
for the button; it passes an action event along by
calling its own processActionEvent method.
The latter method passes the action event on to any action
listeners that have registered an interest in action
events generated by this button.
If an application wants to perform some action based on
a button being pressed and released, it should implement
ActionListener and register the new listener
to receive events from this button, by calling the button's
addActionListener method. The application can
make use of the button's action command as a messaging protocol.
ActionEvent,
ActionListener,
Component.processMouseEvent(java.awt.event.MouseEvent),
Component.addMouseListener(java.awt.event.MouseListener),
Serialized Form| Nested Class Summary | |
protected class |
Button.AccessibleAWTButton
This class implements accessibility support for the Button class. |
| Nested classes inherited from class java.awt.Component |
Component.AccessibleAWTComponent, Component.BltBufferStrategy, Component.FlipBufferStrategy |
| Field Summary |
| Fields inherited from class java.awt.Component |
BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENT |
| Fields inherited from interface java.awt.image.ImageObserver |
ABORT, ALLBITS, ERROR, FRAMEBITS, HEIGHT, PROPERTIES, SOMEBITS, WIDTH |
| Constructor Summary | |
Button()
Constructs a Button with no label. |
|
Button(String label)
Constructs a Button with the specified label. |
|
| Method Summary | |
void |
addActionListener(ActionListener l)
Adds the specified action listener to receive action events from this button. |
void |
addNotify()
Creates the peer of the button. |
AccessibleContext |
getAccessibleContext()
Gets the AccessibleContext associated with
this Button. |
String |
getActionCommand()
Returns the command name of the action event fired by this button. |
ActionListener[] |
getActionListeners()
Returns an array of all the action listeners registered on this button. |
String |
getLabel()
Gets the label of this button. |
EventListener[] |
getListeners(Class listenerType)
Returns an array of all the objects currently registered as FooListeners
upon this Button. |
protected String |
paramString()
Returns a string representing the state of this Button. |
protected void |
processActionEvent(ActionEvent e)
Processes action events occurring on this button by dispatching them to any registered ActionListener objects. |
protected void |
processEvent(AWTEvent e)
Processes events on this button. |
void |
removeActionListener(ActionListener l)
Removes the specified action listener so that it no longer receives action events from this button. |
void |
setActionCommand(String command)
Sets the command name for the action event fired by this button. |
void |
setLabel(String label)
Sets the button's label to be the specified string. |
| Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
| Constructor Detail |
public Button()
throws HeadlessException
HeadlessException - if GraphicsEnvironment.isHeadless()
returns trueGraphicsEnvironment.isHeadless()
public Button(String label)
throws HeadlessException
label - A string label for the button.
HeadlessException - if GraphicsEnvironment.isHeadless()
returns trueGraphicsEnvironment.isHeadless()| Method Detail |
public void addNotify()
addNotify in class ComponentToolkit.createButton(java.awt.Button),
Component.getToolkit()public String getLabel()
null
if the button has no label.setLabel(java.lang.String)public void setLabel(String label)
label - the new label, or null
if the button has no label.getLabel()public void setActionCommand(String command)
command - A string used to set the button's
action command.
If the string is null then the action command
is set to match the label of the button.ActionEventpublic String getActionCommand()
null (default) then this method
returns the label of the button.
public void addActionListener(ActionListener l)
l - the action listenerremoveActionListener(java.awt.event.ActionListener),
getActionListeners(),
ActionListenerpublic void removeActionListener(ActionListener l)
l - the action listeneraddActionListener(java.awt.event.ActionListener),
getActionListeners(),
ActionListenerpublic ActionListener[] getActionListeners()
ActionListeners
or an empty array if no action
listeners are currently registeredaddActionListener(java.awt.event.ActionListener),
removeActionListener(java.awt.event.ActionListener),
ActionListenerpublic EventListener[] getListeners(Class listenerType)
FooListeners
upon this Button.
FooListeners are registered using the
addFooListener method.
You can specify the listenerType argument
with a class literal, such as
FooListener.class.
For example, you can query a
Button b
for its action listeners with the following code:
ActionListener[] als = (ActionListener[])(b.getListeners(ActionListener.class));If no such listeners exist, this method returns an empty array.
getListeners in class ComponentlistenerType - the type of listeners requested; this parameter
should specify an interface that descends from
java.util.EventListener
FooListeners on this button,
or an empty array if no such
listeners have been added
ClassCastException - if listenerType
doesn't specify a class or interface that implements
java.util.EventListenergetActionListeners()protected void processEvent(AWTEvent e)
ActionEvent, this method invokes
the processActionEvent method. Otherwise,
it invokes processEvent on the superclass.
Note that if the event parameter is null
the behavior is unspecified and may result in an
exception.
processEvent in class Componente - the eventActionEvent,
processActionEvent(java.awt.event.ActionEvent)protected void processActionEvent(ActionEvent e)
ActionListener objects.
This method is not called unless action events are enabled for this button. Action events are enabled when one of the following occurs:
ActionListener object is registered
via addActionListener.
enableEvents.
Note that if the event parameter is null
the behavior is unspecified and may result in an
exception.
e - the action eventActionListener,
addActionListener(java.awt.event.ActionListener),
Component.enableEvents(long)protected String paramString()
Button.
This method is intended to be used only for debugging purposes, and the
content and format of the returned string may vary between
implementations. The returned string may be empty but may not be
null.
paramString in class Componentpublic AccessibleContext getAccessibleContext()
AccessibleContext associated with
this Button. For buttons, the
AccessibleContext takes the form of an
AccessibleAWTButton.
A new AccessibleAWTButton instance is
created if necessary.
getAccessibleContext in interface AccessiblegetAccessibleContext in class ComponentAccessibleAWTButton that serves as the
AccessibleContext of this Button
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JavaTM 2 Platform Std. Ed. v1.4.2 |
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Copyright 2003 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Also see the documentation redistribution policy.