Class Button
- java.lang.Object
-
- java.awt.Component
-
- java.awt.Button
- All Implemented Interfaces:
-
ImageObserver
,MenuContainer
,Serializable
,Accessible
public class Button extends Component implements Accessible
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.
- Since:
- 1.0
- See Also:
-
ActionEvent
,ActionListener
,Component.processMouseEvent(java.awt.event.MouseEvent)
,Component.addMouseListener(java.awt.event.MouseListener)
, Serialized Form
Nested Class Summary
Modifier and Type | Class | Description |
---|---|---|
protected class | Button.AccessibleAWTButton | This class implements accessibility support for the |
Nested classes/interfaces declared in class java.awt.Component
Component.AccessibleAWTComponent, Component.BaselineResizeBehavior, Component.BltBufferStrategy, Component.FlipBufferStrategy
Field Summary
Fields declared in class java.awt.Component
accessibleContext, BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENT
Fields declared in interface java.awt.image.ImageObserver
ABORT, ALLBITS, ERROR, FRAMEBITS, HEIGHT, PROPERTIES, SOMEBITS, WIDTH
Constructor Summary
Constructor | Description |
---|---|
Button() | Constructs a button with an empty string for its label. |
Button(String label) | Constructs a button with the specified label. |
Method Summary
Modifier and Type | Method | Description |
---|---|---|
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 |
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. |
<T extends EventListener> | getListeners(Class<T> listenerType) | Returns an array of all the objects currently registered as |
protected String | paramString() | Returns a string representing the state of this |
protected void | processActionEvent(ActionEvent e) | Processes action events occurring on this button by dispatching them to any registered |
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 declared in class java.awt.Component
action, add, addComponentListener, addFocusListener, addHierarchyBoundsListener, addHierarchyListener, addInputMethodListener, addKeyListener, addMouseListener, addMouseMotionListener, addMouseWheelListener, addPropertyChangeListener, addPropertyChangeListener, applyComponentOrientation, areFocusTraversalKeysSet, bounds, checkImage, checkImage, coalesceEvents, contains, contains, createImage, createImage, createVolatileImage, createVolatileImage, deliverEvent, disable, disableEvents, dispatchEvent, doLayout, enable, enable, enableEvents, enableInputMethods, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, getAlignmentX, getAlignmentY, getBackground, getBaseline, getBaselineResizeBehavior, getBounds, getBounds, getColorModel, getComponentAt, getComponentAt, getComponentListeners, getComponentOrientation, getCursor, getDropTarget, getFocusCycleRootAncestor, getFocusListeners, getFocusTraversalKeys, getFocusTraversalKeysEnabled, getFont, getFontMetrics, getForeground, getGraphics, getGraphicsConfiguration, getHeight, getHierarchyBoundsListeners, getHierarchyListeners, getIgnoreRepaint, getInputContext, getInputMethodListeners, getInputMethodRequests, getKeyListeners, getLocale, getLocation, getLocation, getLocationOnScreen, getMaximumSize, getMinimumSize, getMouseListeners, getMouseMotionListeners, getMousePosition, getMouseWheelListeners, getName, getParent, getPreferredSize, getPropertyChangeListeners, getPropertyChangeListeners, getSize, getSize, getToolkit, getTreeLock, getWidth, getX, getY, gotFocus, handleEvent, hasFocus, hide, imageUpdate, inside, invalidate, isBackgroundSet, isCursorSet, isDisplayable, isDoubleBuffered, isEnabled, isFocusable, isFocusCycleRoot, isFocusOwner, isFocusTraversable, isFontSet, isForegroundSet, isLightweight, isMaximumSizeSet, isMinimumSizeSet, isOpaque, isPreferredSizeSet, isShowing, isValid, isVisible, keyDown, keyUp, layout, list, list, list, list, list, locate, location, lostFocus, minimumSize, mouseDown, mouseDrag, mouseEnter, mouseExit, mouseMove, mouseUp, move, nextFocus, paint, paintAll, postEvent, preferredSize, prepareImage, prepareImage, print, printAll, processComponentEvent, processFocusEvent, processHierarchyBoundsEvent, processHierarchyEvent, processInputMethodEvent, processKeyEvent, processMouseEvent, processMouseMotionEvent, processMouseWheelEvent, remove, removeComponentListener, removeFocusListener, removeHierarchyBoundsListener, removeHierarchyListener, removeInputMethodListener, removeKeyListener, removeMouseListener, removeMouseMotionListener, removeMouseWheelListener, removeNotify, removePropertyChangeListener, removePropertyChangeListener, repaint, repaint, repaint, repaint, requestFocus, requestFocus, requestFocus, requestFocus, requestFocusInWindow, requestFocusInWindow, requestFocusInWindow, reshape, resize, resize, revalidate, setBackground, setBounds, setBounds, setComponentOrientation, setCursor, setDropTarget, setEnabled, setFocusable, setFocusTraversalKeys, setFocusTraversalKeysEnabled, setFont, setForeground, setIgnoreRepaint, setLocale, setLocation, setLocation, setMaximumSize, setMinimumSize, setMixingCutoutShape, setName, setPreferredSize, setSize, setSize, setVisible, show, show, size, toString, transferFocus, transferFocusBackward, transferFocusUpCycle, update, validate
Methods declared in class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
Constructor Detail
Button
public Button() throws HeadlessException
Constructs a button with an empty string for its label.
- Throws:
-
HeadlessException
- if GraphicsEnvironment.isHeadless() returns true - See Also:
GraphicsEnvironment.isHeadless()
Button
public Button(String label) throws HeadlessException
Constructs a button with the specified label.
- Parameters:
-
label
- a string label for the button, ornull
for no label - Throws:
-
HeadlessException
- if GraphicsEnvironment.isHeadless() returns true - See Also:
GraphicsEnvironment.isHeadless()
Method Detail
addNotify
public void addNotify()
Creates the peer of the button. The button's peer allows the application to change the look of the button without changing its functionality.
- Overrides:
-
addNotify
in classComponent
- See Also:
Component.getToolkit()
getLabel
public String getLabel()
Gets the label of this button.
- Returns:
- the button's label, or
null
if the button has no label. - See Also:
setLabel(java.lang.String)
setLabel
public void setLabel(String label)
Sets the button's label to be the specified string.
- Parameters:
-
label
- the new label, ornull
if the button has no label. - See Also:
getLabel()
setActionCommand
public void setActionCommand(String command)
Sets the command name for the action event fired by this button. By default this action command is set to match the label of the button.
- Parameters:
-
command
- a string used to set the button's action command. If the string isnull
then the action command is set to match the label of the button. - Since:
- 1.1
- See Also:
ActionEvent
getActionCommand
public String getActionCommand()
Returns the command name of the action event fired by this button. If the command name is null
(default) then this method returns the label of the button.
- Returns:
- the action command name (or label) for this button
addActionListener
public void addActionListener(ActionListener l)
Adds the specified action listener to receive action events from this button. Action events occur when a user presses or releases the mouse over this button. If l is null, no exception is thrown and no action is performed.
Refer to AWT Threading Issues for details on AWT's threading model.
- Parameters:
-
l
- the action listener - Since:
- 1.1
- See Also:
-
removeActionListener(java.awt.event.ActionListener)
,getActionListeners()
,ActionListener
removeActionListener
public void removeActionListener(ActionListener l)
Removes the specified action listener so that it no longer receives action events from this button. Action events occur when a user presses or releases the mouse over this button. If l is null, no exception is thrown and no action is performed.
Refer to AWT Threading Issues for details on AWT's threading model.
- Parameters:
-
l
- the action listener - Since:
- 1.1
- See Also:
-
addActionListener(java.awt.event.ActionListener)
,getActionListeners()
,ActionListener
getActionListeners
public ActionListener[] getActionListeners()
Returns an array of all the action listeners registered on this button.
- Returns:
- all of this button's
ActionListener
s or an empty array if no action listeners are currently registered - Since:
- 1.4
- See Also:
-
addActionListener(java.awt.event.ActionListener)
,removeActionListener(java.awt.event.ActionListener)
,ActionListener
getListeners
public <T extends EventListener> T[] getListeners(Class<T> listenerType)
Returns an array of all the objects currently registered as FooListener
s upon this Button
. FooListener
s 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.
- Overrides:
-
getListeners
in classComponent
- Type Parameters:
-
T
- the type of the listeners - Parameters:
-
listenerType
- the type of listeners requested; this parameter should specify an interface that descends fromjava.util.EventListener
- Returns:
- an array of all objects registered as
FooListener
s on this button, or an empty array if no such listeners have been added - Throws:
-
ClassCastException
- iflistenerType
doesn't specify a class or interface that implementsjava.util.EventListener
- Since:
- 1.3
- See Also:
getActionListeners()
processEvent
protected void processEvent(AWTEvent e)
Processes events on this button. If an event is an instance of 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.
- Overrides:
-
processEvent
in classComponent
- Parameters:
-
e
- the event - Since:
- 1.1
- See Also:
-
ActionEvent
,processActionEvent(java.awt.event.ActionEvent)
processActionEvent
protected void processActionEvent(ActionEvent e)
Processes action events occurring on this button by dispatching them to any registered 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:
- An
ActionListener
object is registered viaaddActionListener
. - Action events are enabled via
enableEvents
.
Note that if the event parameter is null
the behavior is unspecified and may result in an exception.
- Parameters:
-
e
- the action event - Since:
- 1.1
- See Also:
-
ActionListener
,addActionListener(java.awt.event.ActionListener)
,Component.enableEvents(long)
paramString
protected String paramString()
Returns a string representing the state of this 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
.
- Overrides:
-
paramString
in classComponent
- Returns:
- the parameter string of this button
getAccessibleContext
@BeanProperty(expert=true, description="The AccessibleContext associated with this Button.") public AccessibleContext getAccessibleContext()
Gets the AccessibleContext
associated with this Button
. For buttons, the AccessibleContext
takes the form of an AccessibleAWTButton
. A new AccessibleAWTButton
instance is created if necessary.
- Specified by:
-
getAccessibleContext
in interfaceAccessible
- Overrides:
-
getAccessibleContext
in classComponent
- Returns:
- an
AccessibleAWTButton
that serves as theAccessibleContext
of thisButton
- Since:
- 1.3