[Chapter 19] AWTEventMulticaster

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| Chapter 19 java.awt Reference |

# AWTEventMulticaster

## Name

AWTEventMulticaster

##

## Description

This class multicasts events to event listeners. Each multicaster has two listeners, cunningly named `a` and `b`. When an event source calls one of the listener methods of the multicaster, the multicaster calls the same listener method on both `a` and `b`. Multicasters are built into trees using the static `add()` and `remove()` methods. In this way a single event can be sent to many listeners.

Static methods make it easy to implement event multicasting in component subclasses. Each time an `add<type>Listener()` function is called in the component subclass, call the corresponding `AWTEventMulticaster.add()` method to chain together (or "tree up") listeners. Similarly, when a `remove<type>Listener()` function is called, `AWTEventMulticaster.remove()` can be called to remove a chained listener.

## Class Definition

    public class java.awt.AWTEventMulticaster
      extends java.lang.Object
      implements java.awt.event.ActionListener, java.awt.event.AdjustmentListener,
                 java.awt.event.ComponentListener, java.awt.event.ContainerListener,
                 java.awt.event.FocusListener, java.awt.event.ItemListener,
                 java.awt.event.KeyListener, java.awt.event.MouseListener,
                 java.awt.event.MouseMotionListener, java.awt.event.TextListener,
                 java.awt.event.WindowListener {
      // Variables
      protected EventListener a;
      protected EventListener b;
      // Constructors
      protected AWTEventMulticaster(EventListener a, EventListener b);
      // Class Methods
      public static ActionListener add(ActionListener a, ActionListener b);
      public static AdjustmentListener add(AdjustmentListener a,
          AdjustmentListener b);
      public static ComponentListener add(ComponentListener a,
          ComponentListener b);
      public static ContainerListener add(ContainerListener a,
          ContainerListener b);
      public static FocusListener add(FocusListener a, FocusListener b);
      public static ItemListener add(ItemListener a, ItemListener b);
      public static KeyListener add(KeyListener a, KeyListener b);
      public static MouseListener add(MouseListener a, MouseListener b);
      public static MouseMotionListener add(MouseMotionListener a,
          MouseMotionListener b);
      public static TextListener add(TextListener a, TextListener b);
      public static WindowListener add(WindowListener a, WindowListener b);
      protected static EventListener addInternal(EventListener a, EventListener b);
      public static ActionListener remove(ActionListener l, ActionListener oldl);
      public static AdjustmentListener remove(AdjustmentListener l,
          AdjustmentListener oldl);
      public static ComponentListener remove(ComponentListener l,
          ComponentListener oldl);
      public static ContainerListener remove(ContainerListener l,
          ContainerListener oldl);
      public static FocusListener remove(FocusListener l, FocusListener oldl);
      public static ItemListener remove(ItemListener l, ItemListener oldl);
      public static KeyListener remove(KeyListener l, KeyListener oldl);
      public static MouseListener remove(MouseListener l, MouseListener oldl);
      public static MouseMotionListener remove(MouseMotionListener l,
          MouseMotionListener oldl);
      public static TextListener remove(TextListener l, TextListener oldl);
      public static WindowListener remove(WindowListener l, WindowListener;
      protected static EventListener removeInternal(EventListener l,
          EventListener oldl);
      // Instance Methods
      public void actionPerformed(ActionEvent e);
      public void adjustmentValueChanged(AdjustmentEvent e);
      public void componentAdded(ContainerEvent e);
      public void componentHidden(ComponentEvent e);
      public void componentMoved(ComponentEvent e);
      public void componentRemoved(ContainerEvent e);
      public void componentResized(ComponentEvent e);
      public void componentShown(ComponentEvent e);
      public void focusGained(FocusEvent e);
      public void focusLost(FocusEvent e);
      public void itemStateChanged(ItemEvent e);
      public void keyPressed(KeyEvent e);
      public void keyReleased(KeyEvent e);
      public void keyTyped(KeyEvent e);
      public void mouseClicked(MouseEvent e);
      public void mouseDragged(MouseEvent e);
      public void mouseEntered(MouseEvent e);
      public void mouseExited(MouseEvent e);
      public void mouseMoved(MouseEvent e);
      public void mousePressed(MouseEvent e);
      public void mouseReleased(MouseEvent e);
      public void textValueChanged(TextEvent e);
      public void windowActivated(WindowEvent e);
      public void windowClosed(WindowEvent e);
      public void windowClosing(WindowEvent e);
      public void windowDeactivated(WindowEvent e);
      public void windowDeiconified(WindowEvent e);
      public void windowIconified(WindowEvent e);
      public void windowOpened(WindowEvent e);
      // Protected Instance Methods
      protected EventListener remove(EventListener oldl);
      protected void saveInternal(ObjectOutputStream s, String k) throws IOException;
    }

## Variables

### a

#### protected EventListener a

One of the `EventListener`s this `AWTEventMulticaster` sends events to.

### b

#### protected EventListener b

One of the `EventListener`s this `AWTEventMulticaster` sends events to.

## Constructors

### AWTEventMulticaster

#### protected AWTEventMulticaster (EventListener a, EventListener b)

Parameters

  a

    A listener that receives events.

  b

    A listener that receives events.

Description

  Constructs an `AWTEventMulticaster` that sends events it receives to the supplied listeners. The constructor is protected because it is only the class methods of `AWTEventMulticaster` that ever instantiate this class.

## Class Methods

### add

#### public static ActionListener add (ActionListener a, ActionListener b)

Parameters

  a

    An event listener.

  b

    An event listener.

Returns

  A listener object that passes events to `a` and `b`.

#### public static AdjustmentListener add (AdjustmentListener a, AdjustmentListener b)

Parameters

  a

    An event listener.

  b

    An event listener.

Returns

  A listener object that passes events to `a` and `b`.

#### public static ComponentListener add (ComponentListener a, ComponentListener b)

Parameters

  a

    An event listener.

  b

    An event listener.

Returns

  A listener object that passes events to `a` and `b`.

#### public static ContainerListener add (ContainerListener a, ContainerListener b)

Parameters

  a

    An event listener.

  b

    An event listener.

Returns

  A listener object that passes events to `a` and `b`.

#### public static FocusListener add (FocusListener a, FocusListener b)

Parameters

  a

    An event listener.

  b

    An event listener.

Returns

  A listener object that passes events to `a` and `b`.

#### public static ItemListener add (ItemListener a, ItemListener b)

Parameters

  a

    An event listener.

  b

    An event listener.

Returns

  A listener object that passes events to `a` and `b`.

#### public static KeyListener add (KeyListener a, KeyListener b)

Parameters

  a

    An event listener.

  b

    An event listener.

Returns

  A listener object that passes events to `a` and `b`.

#### public static MouseListener add (MouseListener a, MouseListener b)

Parameters

  a

    An event listener.

  b

    An event listener.

Returns

  A listener object that passes events to `a` and `b`.

#### public static MouseMotionListener add (MouseMotionListener a, MouseMotionListener b)

Parameters

  a

    An event listener.

  b

    An event listener.

Returns

  A listener object that passes events to `a` and `b`.

#### public static TextListener add (TextListener a, TextListener b)

Parameters

  a

    An event listener.

  b

    An event listener.

Returns

  A listener object that passes events to `a` and `b`.

#### public static WindowListener add (WindowListener a, WindowListener b)

Parameters

  a

    An event listener.

  b

    An event listener.

Returns

  A listener object that passes events to `a` and `b`.

### addInternal

#### public static EventListener addInternal (EventListener a, EventListener b)

Parameters

  a

    An event listener.

  b

    An event listener.

Returns

  A listener object that passes events to `a` and `b`.

Description

  This method is a helper for the `add()` methods.

### remove

#### public static ActionListener remove (ActionListener l, ActionListener oldl)

Parameters

  l

    An event listener.

  oldl

    An event listener.

Returns

  A listener object that multicasts to `l` but not `oldl`.

#### public static AdjustmentListener remove (AdjustmentListener l, AdjustmentListener oldl)

Parameters

  l

    An event listener.

  oldl

    An event listener.

Returns

  A listener object that multicasts to `l` but not `oldl`.

#### public static ComponentListener remove (ComponentListener l, ComponentListener oldl)

Parameters

  l

    An event listener.

  oldl

    An event listener.

Returns

  A listener object that multicasts to `l` but not `oldl`.

#### public static ContainerListener remove (ContainerListener l, ContainerListener oldl)

Parameters

  l

    An event listener.

  oldl

    An event listener.

Returns

  A listener object that multicasts to `l` but not `oldl`.

#### public static FocusListener remove (FocusListener l, FocusListener oldl)

Parameters

  l

    An event listener.

  oldl

    An event listener.

Returns

  A listener object that multicasts to `l` but not `oldl`.

#### public static ItemListener remove (ItemListener l, ItemListener oldl)

Parameters

  l

    An event listener.

  oldl

    An event listener.

Returns

  A listener object that multicasts to `l` but not `oldl`.

#### public static KeyListener remove (KeyListener l, KeyListener oldl)

Parameters

  l

    An event listener.

  oldl

    An event listener.

Returns

  A listener object that multicasts to `l` but not `oldl`.

#### public static MouseListener remove (MouseListener l, MouseListener oldl)

Parameters

  l

    An event listener.

  oldl

    An event listener.

Returns

  A listener object that multicasts to `l` but not `oldl`.

#### public static MouseMotionListener remove (MouseMotionListener l, MouseMotionListener oldl)

Parameters

  l

    An event listener.

  oldl

    An event listener.

Returns

  A listener object that multicasts to `l` but not `oldl`.

#### public static TextListener remove (TextListener l, TextListener oldl)

Parameters

  l

    An event listener.

  oldl

    An event listener.

Returns

  A listener object that multicasts to `l` but not `oldl`.

#### public static WindowListener remove (WindowListener l, WindowListener oldl)

Parameters

  l

    An event listener.

  oldl

    An event listener.

Returns

  A listener object that multicasts to `l` but not `oldl`.

#### public static WindowListener remove (WindowListener l, WindowListener oldl)

Parameters

  l

    An event listener.

  oldl

    An event listener.

Returns

  A listener object that multicasts to `l` but not `oldl`.

### removeInternal

#### public static EventListener removeInternal (EventListener l, EventListener oldl)

Parameters

  l

    An event listener.

  oldl

    An event listener.

Returns

  A listener object that multicasts to `l` but not `oldl`.

Description

  This method is a helper for the `remove()` methods.

## Instance Methods

### actionPerformed

#### public void actionPerformed (ActionEvent e)

Parameters

  e

    The action event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### adjustmentValueChanged

#### public void adjustmentValueChanged (AdjustmentEvent e)

Parameters

  e

    The adjustment event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### componentAdded

#### public void componentAdded (ContainerEvent e)

Parameters

  e

    The container event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### componentHidden

#### public void componentHidden (ComponentEvent e)

Parameters

  e

    The component event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### componentMoved

#### public void componentMoved (ComponentEvent e)

Parameters

  e

    The component event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### componentRemoved

#### public void componentRemoved (ContainerEvent e)

Parameters

  e

    The container event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### componentResized

#### public void componentResized (ComponentEvent e)

Parameters

  e

    The component event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### componentShown

#### public void componentShown (ComponentEvent e)

Parameters

  e

    The component event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### focusGained

#### public void focusGained (FocusEvent e)

Parameters

  e

    The focus event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### focusLost

#### public void focusLost (FocusEvent e)

Parameters

  e

    The focus event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### itemStateChanged

#### public void itemStateChanged (ItemEvent e)

Parameters

  e

    The item event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### keyPressed

#### public void keyPressed (KeyEvent e)

Parameters

  e

    The key event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### keyReleased

#### public void keyReleased (KeyEvent e)

Parameters

  e

    The key event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### keyTyped

#### public void keyTyped (KeyEvent e)

Parameters

  e

    The key event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### mouseClicked

#### public void mouseClicked (MouseEvent e)

Parameters

  e

    The mouse event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### mouseDragged

#### public void mouseDragged (MouseEvent e)

Parameters

  e

    The mouse event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### mouseEntered

#### public void mouseEntered (MouseEvent e)

Parameters

  e

    The mouse event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### mouseExited

#### public void mouseExited (MouseEvent e)

Parameters

  e

    The mouse event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### mouseMoved

#### public void mouseMoved (MouseEvent e)

Parameters

  e

    The mouse event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### mousePressed

#### public void mousePressed (MouseEvent e)

Parameters

  e

    The mouse event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### mouseReleased

#### public void mouseReleased (MouseEvent e)

Parameters

  e

    The mouse event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### textValueChanged

#### public void textValueChanged (TextEvent e)

Parameters

  e

    The text event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### windowActivated

#### public void windowActivated (WindowEvent e)

Parameters

  e

    The window event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### windowClosed

#### public void windowClosed (WindowEvent e)

Parameters

  e

    The window event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### windowClosing

#### public void windowClosing (WindowEvent e)

Parameters

  e

    The window event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### windowDeactivated

#### public void windowDeactivated (WindowEvent e)

Parameters

  e

    The window event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### windowDeiconified

#### public void windowDeiconified (WindowEvent e)

Parameters

  e

    The window event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### windowIconified

#### public void windowIconified (WindowEvent e)

Parameters

  e

    The window event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

### windowOpened

#### public void windowOpened (WindowEvent e)

Parameters

  e

    The window event that occurred.

Description

  Handles the event by passing it on to listeners `a` and `b`.

## Protected Instance Methods

### remove

#### protected EventListener remove(EventListener oldl)

Parameters

  oldl

    The listener to remove.

Returns

  The resulting `EventListener`.

Description

  This method removes `oldl` from the `AWTEventMulticaster` and returns the resulting listener.

## See Also

`ActionEvent`, `AdjustmentEvent`, `ComponentEvent`, `Event`, `EventListener`, `EventObject`, `FocusEvent`, `ItemEvent`, `KeyEvent`, `MouseEvent`, `WindowEvent`

AWTEvent |  | AWTException