Button (Java Platform SE 8 )
Keywords: java.awt.Button class
Date: 2016-12-09

java.awt

## 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:
    JDK1.0
  See Also:
    `ActionEvent`, `ActionListener`, `Component.processMouseEvent(java.awt.event.MouseEvent)`, `Component.addMouseListener(java.awt.event.MouseListener)`, Serialized Form

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `protected class` | `Button.AccessibleAWTButton` This class implements accessibility support for the `Button` class.

    - ### Nested classes/interfaces inherited from class java.awt.Component

      `Component.AccessibleAWTComponent, Component.BaselineResizeBehavior, Component.BltBufferStrategy, Component.FlipBufferStrategy`

  - ### Field Summary

    - ### Fields inherited from class java.awt.Component

      `accessibleContext, 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

    Constructors
    Constructor and Description
    `Button()` Constructs a button with an empty string for its label.
    `Button(String label)` Constructs a button with the specified label.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and 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 `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.
    `<T extends EventListener> T[]` | `getListeners(Class<T> listenerType)` Returns an array of all the objects currently registered as `FooListener`s 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.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, getPeer, 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, requestFocusInWindow, requestFocusInWindow, reshape, resize, resize, revalidate, setBackground, setBounds, setBounds, setComponentOrientation, setCursor, setDropTarget, setEnabled, setFocusable, setFocusTraversalKeys, setFocusTraversalKeysEnabled, setFont, setForeground, setIgnoreRepaint, setLocale, setLocation, setLocation, setMaximumSize, setMinimumSize, setName, setPreferredSize, setSize, setSize, setVisible, show, show, size, toString, transferFocus, transferFocusBackward, transferFocusUpCycle, update, validate`

    - ### Methods inherited from 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, or `null` 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 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.

      Refer to AWT Threading Issues for details on AWT's threading model.

      Parameters:
        `l` - the action listener
      Since:
        JDK1.1
      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:
        JDK1.1
      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 class `Component`
      Parameters:
        `listenerType` - the type of listeners requested; this parameter should specify an interface that descends from `java.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` - if `listenerType` doesn't specify a class or interface that implements `java.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 class `Component`
      Parameters:
        `e` - the event
      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`.

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

      Parameters:
        `e` - the action event
      Since:
        JDK1.1
      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 class `Component`
      Returns:
        the parameter string of this button

    - #### getAccessibleContext

          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 interface `Accessible`
      Overrides:
        `getAccessibleContext` in class `Component`
      Returns:
        an `AccessibleAWTButton` that serves as the `AccessibleContext` of this `Button`
      Since:
        1.3

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