java.awt
Class Button

java.lang.Object
  |
  +--java.awt.Component
        |
        +--java.awt.Button

public class Button

extends Component

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:

JDK1.0

See Also:

ActionEvent, ActionListener, Component.processMouseEvent(java.awt.event.MouseEvent), Component.addMouseListener(java.awt.event.MouseListener), Serialized Form

Fields inherited from class java.awt.Component

BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENT

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.
String	getActionCommand() Returns the command name of the action event fired by this button.
String	getLabel() Gets the label of this button.
protected String	paramString() Returns the parameter 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.awt.Component

action, add, addComponentListener, addFocusListener, addInputMethodListener, addKeyListener, addMouseListener, addMouseMotionListener, addPropertyChangeListener, addPropertyChangeListener, bounds, checkImage, checkImage, coalesceEvents, contains, contains, createImage, createImage, deliverEvent, disable, disableEvents, dispatchEvent, doLayout, enable, enable, enableEvents, enableInputMethods, firePropertyChange, getAlignmentX, getAlignmentY, getBackground, getBounds, getBounds, getColorModel, getComponentAt, getComponentAt, getComponentOrientation, getCursor, getDropTarget, getFont, getFontMetrics, getForeground, getGraphics, getHeight, getInputContext, getInputMethodRequests, getLocale, getLocation, getLocation, getLocationOnScreen, getMaximumSize, getMinimumSize, getName, getParent, getPeer, getPreferredSize, getSize, getSize, getToolkit, getTreeLock, getWidth, getX, getY, gotFocus, handleEvent, hasFocus, hide, imageUpdate, inside, invalidate, isDisplayable, isDoubleBuffered, isEnabled, isFocusTraversable, isLightweight, isOpaque, 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, processInputMethodEvent, processKeyEvent, processMouseEvent, processMouseMotionEvent, remove, removeComponentListener, removeFocusListener, removeInputMethodListener, removeKeyListener, removeMouseListener, removeMouseMotionListener, removeNotify, removePropertyChangeListener, removePropertyChangeListener, repaint, repaint, repaint, repaint, requestFocus, reshape, resize, resize, setBackground, setBounds, setBounds, setComponentOrientation, setCursor, setDropTarget, setEnabled, setFont, setForeground, setLocale, setLocation, setLocation, setName, setSize, setSize, setVisible, show, show, size, toString, transferFocus, update, validate

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

Button

public Button()

Constructs a Button with no label.

Button

public Button(String label)

Constructs a Button with the specified label.

Parameters:

label - A string label for the button.

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 class Component

See Also:

Toolkit.createButton(java.awt.Button), 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, or null 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 is null then the action command is set to match the label of the button.

Since:

JDK1.1

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.

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.

Parameters:

l - the action listener

Since:

JDK1.1

See Also:

ActionListener, removeActionListener(java.awt.event.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.

Parameters:

l - the action listener

Since:

JDK1.1

See Also:

ActionListener, addActionListener(java.awt.event.ActionListener)

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.

Parameters:

e - the event.

Overrides:

processEvent in class Component

Since:

JDK1.1

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 via addActionListener.
• Action events are enabled via enableEvents.

Parameters:

e - the action event.

Since:

JDK1.1

See Also:

ActionListener, addActionListener(java.awt.event.ActionListener), Component.enableEvents(long)

paramString

protected String paramString()

Returns the parameter string representing the state of this button. This string is useful for debugging.

Returns:

the parameter string of this button.

Overrides:

paramString in class Component