java.awt.Button

public class java.awt

Button

Java SE 6

Extends: Component

Implements: Accessible

Inner classes: Button.AccessibleAWTButton

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.

version 1.82 07/11/06

since JDK1.0

See also java.awt.event.ActionEvent, java.awt.event.ActionListener, processMouseEvent, addMouseListener

Constructors

public

Button() throws HeadlessException Details

Constructs a button with an empty string for its label.

Throws	HeadlessException: if GraphicsEnvironment.isHeadless() returns true
See also	isHeadless

public

Button(String label) throws HeadlessException Details

Constructs a button with the specified label.

label	a string label for the button, or `null` for no label
Throws	HeadlessException: if GraphicsEnvironment.isHeadless() returns true
See also	isHeadless

Methods

public void

addActionListener(ActionListener l) Details

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.

l the action listener

since JDK1.1

See also removeActionListener, getActionListeners, java.awt.event.ActionListener

public void

addNotify() Details

Creates the peer of the button. The button's peer allows the application to change the look of the button without changing its functionality.

See also

createButton(java.awt.Button), getToolkit()

protected String

paramString() Details

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.

return

the parameter string of this button

protected void

processActionEvent(ActionEvent e) Details

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.

Note that if the event parameter is null the behavior is unspecified and may result in an exception.

e the action event

since JDK1.1

See also java.awt.event.ActionListener, addActionListener, enableEvents

protected void

processEvent(AWTEvent e) Details

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.

e the event

since JDK1.1

See also java.awt.event.ActionEvent, processActionEvent

public void

removeActionListener(ActionListener l) Details

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.

l the action listener

since JDK1.1

See also addActionListener, getActionListeners, java.awt.event.ActionListener

Properties

public AccessibleContext

getAccessibleContext() Details

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.

return	an `AccessibleAWTButton` that serves as the `AccessibleContext` of this `Button`
beaninfo	expert: true description: The AccessibleContext associated with this Button.
since	1.3

public void

setActionCommand(String command) Details

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.

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	java.awt.event.ActionEvent

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.

public ActionListener[]

getActionListeners() Details

Returns an array of all the action listeners registered on this button.

return	all of this button's `ActionListener`s or an empty array if no action listeners are currently registered
since	1.4
See also	addActionListener, removeActionListener, java.awt.event.ActionListener

public void

setLabel(String label) Details

Sets the button's label to be the specified string.

label	the new label, or `null` if the button has no label.
See also	getLabel

public String

getLabel() Details

Gets the label of this button.

return	the button's label, or `null` if the button has no label.
See also	setLabel

public EventListener[]<T>

getListeners(Class listenerType) Details

Returns an array of all the objects currently registered as 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.

listenerType	the type of listeners requested; this parameter should specify an interface that descends from `java.util.EventListener`
return	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: if `listenerType` doesn't specify a class or interface that implements `java.util.EventListener`
since	1.3
See also	getActionListeners

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Java SE 6

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