JAVA --- 之事件处理---源码剖析（部分转载+自己提炼）

------------定义一个事件类------------------

import java.util.EventObject;

public class DoorEvent extends EventObject {
    private String doorState = "";

    public DoorEvent(Object source, String doorState) {
        super(source);
        this.doorState = doorState;
    }

    public void setDoorState(String doorState) {
        this.doorState = doorState;
    }

    public String getDoorState() {
        return this.doorState;
    }
}
--------------定义事件监听器------------

import java.util.EventListener;

public interface DoorListener extends EventListener {//这个EventListener接口中没有方法。
    public void doorEvent(DoorEvent event);
}

-------------------接口的实现类1-------------------

public class DoorListener1 implements DoorListener {

    @Override
    public void doorEvent(DoorEvent event) {
        if (event.getDoorState() != null && event.getDoorState().equals("open")) {
            System.out.println("1 opened");
        } else {
            System.out.println("1 closed");
        }
    }

}

--------------------接口的实现类2--------------------

public class DoorListener2 implements DoorListener {

    @Override
    public void doorEvent(DoorEvent event) {
        if (event.getDoorState() != null && event.getDoorState().equals("open")) {
            System.out.println("2 opened");
        } else {
            System.out.println("2 closed");
        }
    }

}

------------------------产生事件的源类，可以想成是Button类，在它上面点击下会产生事件-----------------------------

import java.util.Collection;
import java.util.HashSet;
import java.util.Iterator;

public class DoorManager {
    private Collection<DoorListener> listeners;

    public void addDoorListener(DoorListener listener) {
        if (listeners == null) {
            listeners = new HashSet<DoorListener>();
        }
        listeners.add(listener);
    }

    public void removeDoorListener(DoorListener listener) {
        if (listeners == null)
            return;
        listeners.remove(listener);
    }

    protected void fireWorkspaceOpened() {
        if (listeners == null)
            return;
        DoorEvent event = new DoorEvent(this, "open");
        notifyListeners(event);
    }

    protected void fireWorkspaceClosed() {
        if (listeners == null)
            return;
        DoorEvent event = new DoorEvent(this, "close");
        notifyListeners(event);
    }

    private void notifyListeners(DoorEvent event) {
        Iterator<DoorListener> iter = listeners.iterator();
        while (iter.hasNext()) {
            DoorListener listener = iter.next();
            listener.doorEvent(event);
        }
    }
}

-----------------------测试程序------------------------------

public class DoorMain {
    public static void main(String[] args) {
        
        DoorManager manager = new DoorManager();
        
        manager.addDoorListener(new DoorListener1());
        manager.addDoorListener(new DoorListener2());

        manager.fireWorkspaceOpened();//这个可以想像成我们点击了Button.即触发了事件
        
        System.out.println("============");
        
        manager.fireWorkspaceClosed();//这个可以想像成我们点击了Button..即触发了事件
    }
}

--------------------输出结果------------------

2 opened
1 opened
============
2 closed
1 closed

------------------最后我们再来看看理论吧！------------------------------

java中的事件机制的参与者有3种角色：

1.event object：事件状态对象，用于listener的相应的方法之中，作为参数，一般存在与listerner的方法之中

2.event source：具体的事件源，比如说，你点击一个button，那么button就是event source，要想使button对某些事件进行响应，你就需要注册特定的listener。

3.event listener：具体的对监听的事件类，当它监听到event object产生的时候，它就调用相应的方法，进行处理。

先看看jdk提供的event包：
public interface EventListener：所有事件侦听器接口必须扩展的标记接口。
public class EventObject extends Object implements Serializable
所有事件状态对象都将从其派生的根类。 所有 Event 在构造时都引用了对象 "source"，在逻辑上认为该对象是最初发生有关 Event 的对象。

     在Java2处理事件时，没有采用dispatchEvent()-postEvent()-handleEvent()方式，采用了监听器类，每个事件类都有相关联的监听器接口。事件从事件源到监听者的传递是通过对目标监听者对象的Java方法调用进行的。

　　对每个明确的事件的发生，都相应地定义一个明确的Java方法。这些方法都集中定义在事件监听者（EventListener）接口中，这个接口要继承 java.util.EventListener。 实现了事件监听者接口中一些或全部方法的类就是事件监听者。

　　伴随着事件的发生，相应的状态通常都封装在事件状态对象中，该对象必须继承 自java.util.EventObject。事件状态对象作为单参传递给应响应该事件的监听者方法中。发出某种特定事件的事件源的标识是：遵从规定的 设计格式为事件监听者定义注册方法，并接受对指定事件监听者接口实例的引用。

首先问个问题：您熟悉java.util.EventObject 和java.util.EventListener两个类以及他们已有的子类吗？

如果你已经能够熟练使用jdk为我们提供的事件监听器，并且很熟悉 MouseEvent, KeyEvent, WindowEvent等等这些jdk为我们准备好的事件，那么想必你对java的事件机制已经有所理解。但是也许你还是觉得虽然用起来没什么问题，但是 原理还是有些糊涂，那么下面我们再进一步自己实现这些事件和监听器，即自定义事件。

其实自定义事件在java中很有用处，我们有的时候想让自己的程序产生一个事 件，但有不希望（或者不可能）用鼠标，键盘之类的输入设备进行操作，比如你写一个应用程序，在这个程序中一旦收到邮件就对邮件进行相关处理，对于“收到邮 件”这个事件，jdk中就没有定义。对于这样的事件，以及对于这样的事件的监听器，我们只能自己动手完成了。

---------------------------对照一下，java图形化编程时的事件处理----------------------------------

我们只要实现自己的Listener，及往事件源中注册监听器，就行。事件类由jdk为我们提供。

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

class SimpleListener implements ActionListener {
    public void actionPerformed(ActionEvent e) {
        String buttonName = e.getActionCommand();
        if (buttonName.equals("按钮1"))
            System.out.println("按钮1 被点击");

    }
}

public class ActionTest {
    private static JFrame frame;
    private static JPanel myPanel;
    private JButton button1;

    public ActionTest() {
        myPanel = new JPanel();
        button1 = new JButton("按钮1");
        SimpleListener ourListener = new SimpleListener();
        button1.addActionListener(ourListener);
        myPanel.add(button1);

    }

    public static void main(String s[]) {
        ActionTest gui = new ActionTest();

        frame = new JFrame("Simple1");
        frame.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });

        frame.getContentPane().add(myPanel);
        frame.pack();
        frame.setVisible(true);
    }
}

---------------------下面我们来看看jdk中的这些类的实现吧-----------------------------

事件类

public class ActionEvent extends AWTEvent {//稍后再看看AWTEvent类。

    /**
     * The shift modifier. An indicator that the shift key was held
     * down during the event.
     */
    public static final int SHIFT_MASK          = Event.SHIFT_MASK;

    /**
     * The control modifier. An indicator that the control key was held
     * down during the event.
     */
    public static final int CTRL_MASK           = Event.CTRL_MASK;

    /**
     * The meta modifier. An indicator that the meta key was held
     * down during the event.
     */
    public static final int META_MASK           = Event.META_MASK;

    /**
     * The alt modifier. An indicator that the alt key was held
     * down during the event.
     */
    public static final int ALT_MASK            = Event.ALT_MASK;


    /**
     * The first number in the range of ids used for action events.
     */
    public static final int ACTION_FIRST                = 1001;

    /**
     * The last number in the range of ids used for action events.
     */
    public static final int ACTION_LAST                 = 1001;

    /**
     * This event id indicates that a meaningful action occured.
     */
    public static final int ACTION_PERFORMED    = ACTION_FIRST; //Event.ACTION_EVENT

    /**
     * The nonlocalized string that gives more details
     * of what actually caused the event.
     * This information is very specific to the component
     * that fired it.

     * @serial
     * @see #getActionCommand
     */
    String actionCommand;

    /**
     * Timestamp of when this event occurred. Because an ActionEvent is a high-
     * level, semantic event, the timestamp is typically the same as an
     * underlying InputEvent.
     *
     * @serial
     * @see #getWhen
     */
    long when;

    /**
     * This represents the key modifier that was selected,
     * and is used to determine the state of the selected key.
     * If no modifier has been selected it will default to
     * zero.
     *
     * @serial
     * @see #getModifiers
     */
    int modifiers;

    /*
     * JDK 1.1 serialVersionUID
     */
    private static final long serialVersionUID = -7671078796273832149L;

    /**
     * Constructs an <code>ActionEvent</code> object.
     * <p>
     * This method throws an
     * <code>IllegalArgumentException</code> if <code>source</code>
     * is <code>null</code>.
     * A <code>null</code> <code>command</code> string is legal,
     * but not recommended.
     *
     * @param source  The object that originated the event
     * @param id      An integer that identifies the event.
     *                     For information on allowable values, see
     *                     the class description for {@link ActionEvent}
     * @param command A string that may specify a command (possibly one
     *                of several) associated with the event
     * @throws IllegalArgumentException if <code>source</code> is null
     * @see #getSource()
     * @see #getID()
     * @see #getActionCommand()
     */
    public ActionEvent(Object source, int id, String command) {
        this(source, id, command, 0);
    }

    /**
     * Constructs an <code>ActionEvent</code> object with modifier keys.
     * <p>
     * This method throws an
     * <code>IllegalArgumentException</code> if <code>source</code>
     * is <code>null</code>.
     * A <code>null</code> <code>command</code> string is legal,
     * but not recommended.
     *
     * @param source  The object that originated the event
     * @param id      An integer that identifies the event.
     *                     For information on allowable values, see
     *                     the class description for {@link ActionEvent}
     * @param command A string that may specify a command (possibly one
     *                of several) associated with the event
     * @param modifiers The modifier keys down during event
     *                  (shift, ctrl, alt, meta).
     *                  Passing negative parameter is not recommended.
     *                  Zero value means that no modifiers were passed
     * @throws IllegalArgumentException if <code>source</code> is null
     * @see #getSource()
     * @see #getID()
     * @see #getActionCommand()
     * @see #getModifiers()
     */
    public ActionEvent(Object source, int id, String command, int modifiers) {
        this(source, id, command, 0, modifiers);
    }

    /**
     * Constructs an <code>ActionEvent</code> object with the specified
     * modifier keys and timestamp.
     * <p>
     * This method throws an
     * <code>IllegalArgumentException</code> if <code>source</code>
     * is <code>null</code>.
     * A <code>null</code> <code>command</code> string is legal,
     * but not recommended.
     *
     * @param source    The object that originated the event
     * @param id      An integer that identifies the event.
     *                     For information on allowable values, see
     *                     the class description for {@link ActionEvent}
     * @param command A string that may specify a command (possibly one
     *                of several) associated with the event
     * @param modifiers The modifier keys down during event
     *                  (shift, ctrl, alt, meta).
     *                  Passing negative parameter is not recommended.
     *                  Zero value means that no modifiers were passed
     * @param when   A long that gives the time the event occurred.
     *               Passing negative or zero value
     *               is not recommended
     * @throws IllegalArgumentException if <code>source</code> is null
     * @see #getSource()
     * @see #getID()
     * @see #getActionCommand()
     * @see #getModifiers()
     * @see #getWhen()
     *
     * @since 1.4
     */
    public ActionEvent(Object source, int id, String command, long when,
                       int modifiers) {
        super(source, id);
        this.actionCommand = command;
        this.when = when;
        this.modifiers = modifiers;
    }

    /**
     * Returns the command string associated with this action.
     * This string allows a "modal" component to specify one of several
     * commands, depending on its state. For example, a single button might
     * toggle between "show details" and "hide details". The source object
     * and the event would be the same in each case, but the command string
     * would identify the intended action.
     * <p>
     * Note that if a <code>null</code> command string was passed
     * to the constructor for this <code>ActionEvent</code>, this
     * this method returns <code>null</code>.
     *
     * @return the string identifying the command for this event
     */
    public String getActionCommand() {
        return actionCommand;
    }

    /**
     * Returns the timestamp of when this event occurred. Because an
     * ActionEvent is a high-level, semantic event, the timestamp is typically
     * the same as an underlying InputEvent.
     *
     * @return this event's timestamp
     * @since 1.4
     */
    public long getWhen() {
        return when;
    }

    /**
     * Returns the modifier keys held down during this action event.
     *
     * @return the bitwise-or of the modifier constants
     */
    public int getModifiers() {
        return modifiers;
    }

    /**
     * Returns a parameter string identifying this action event.
     * This method is useful for event-logging and for debugging.
     *
     * @return a string identifying the event and its associated command
     */
    public String paramString() {
        String typeStr;
        switch(id) {
          case ACTION_PERFORMED:
              typeStr = "ACTION_PERFORMED";
              break;
          default:
              typeStr = "unknown type";
        }
        return typeStr + ",cmd="+actionCommand+",when="+when+",modifiers="+
            KeyEvent.getKeyModifiersText(modifiers);
    }
}

AWTEvent类：

public abstract class AWTEvent extends EventObject {//看到了吧。还是从EventObject来的。
    private static final PlatformLogger log = PlatformLogger.getLogger("java.awt.AWTEvent");
    private byte bdata[];

    /**
     * The event's id.
     * @serial
     * @see #getID()
     * @see #AWTEvent
     */
    protected int id;

    /**
     * Controls whether or not the event is sent back down to the peer once the
     * source has processed it - false means it's sent to the peer; true means
     * it's not. Semantic events always have a 'true' value since they were
     * generated by the peer in response to a low-level event.
     * @serial
     * @see #consume
     * @see #isConsumed
     */
    protected boolean consumed = false;

   /*
    * The event's AccessControlContext.
    */
    private transient volatile AccessControlContext acc =
        AccessController.getContext();

   /*
    * Returns the acc this event was constructed with.
    */
    final AccessControlContext getAccessControlContext() {
        if (acc == null) {
            throw new SecurityException("AWTEvent is missing AccessControlContext");
        }
        return acc;
    }

    transient boolean focusManagerIsDispatching = false;
    transient boolean isPosted;

    /**
     * Indicates whether this AWTEvent was generated by the system as
     * opposed to by user code.
     */
    private transient boolean isSystemGenerated;

    /**
     * The event mask for selecting component events.
     */
    public final static long COMPONENT_EVENT_MASK = 0x01;

    /**
     * The event mask for selecting container events.
     */
    public final static long CONTAINER_EVENT_MASK = 0x02;

    /**
     * The event mask for selecting focus events.
     */
    public final static long FOCUS_EVENT_MASK = 0x04;

    /**
     * The event mask for selecting key events.
     */
    public final static long KEY_EVENT_MASK = 0x08;

    /**
     * The event mask for selecting mouse events.
     */
    public final static long MOUSE_EVENT_MASK = 0x10;

    /**
     * The event mask for selecting mouse motion events.
     */
    public final static long MOUSE_MOTION_EVENT_MASK = 0x20;

    /**
     * The event mask for selecting window events.
     */
    public final static long WINDOW_EVENT_MASK = 0x40;

    /**
     * The event mask for selecting action events.
     */
    public final static long ACTION_EVENT_MASK = 0x80;

    /**
     * The event mask for selecting adjustment events.
     */
    public final static long ADJUSTMENT_EVENT_MASK = 0x100;

    /**
     * The event mask for selecting item events.
     */
    public final static long ITEM_EVENT_MASK = 0x200;

    /**
     * The event mask for selecting text events.
     */
    public final static long TEXT_EVENT_MASK = 0x400;

    /**
     * The event mask for selecting input method events.
     */
    public final static long INPUT_METHOD_EVENT_MASK = 0x800;

    /**
     * The pseudo event mask for enabling input methods.
     * We're using one bit in the eventMask so we don't need
     * a separate field inputMethodsEnabled.
     */
    final static long INPUT_METHODS_ENABLED_MASK = 0x1000;

    /**
     * The event mask for selecting paint events.
     */
    public final static long PAINT_EVENT_MASK = 0x2000;

    /**
     * The event mask for selecting invocation events.
     */
    public final static long INVOCATION_EVENT_MASK = 0x4000;

    /**
     * The event mask for selecting hierarchy events.
     */
    public final static long HIERARCHY_EVENT_MASK = 0x8000;

    /**
     * The event mask for selecting hierarchy bounds events.
     */
    public final static long HIERARCHY_BOUNDS_EVENT_MASK = 0x10000;

    /**
     * The event mask for selecting mouse wheel events.
     * @since 1.4
     */
    public final static long MOUSE_WHEEL_EVENT_MASK = 0x20000;

    /**
     * The event mask for selecting window state events.
     * @since 1.4
     */
    public final static long WINDOW_STATE_EVENT_MASK = 0x40000;

    /**
     * The event mask for selecting window focus events.
     * @since 1.4
     */
    public final static long WINDOW_FOCUS_EVENT_MASK = 0x80000;

    /**
     * WARNING: there are more mask defined privately.  See
     * SunToolkit.GRAB_EVENT_MASK.
     */

    /**
     * The maximum value for reserved AWT event IDs. Programs defining
     * their own event IDs should use IDs greater than this value.
     */
    public final static int RESERVED_ID_MAX = 1999;

    // security stuff
    private static Field inputEvent_CanAccessSystemClipboard_Field = null;

    /*
     * JDK 1.1 serialVersionUID
     */
    private static final long serialVersionUID = -1825314779160409405L;

    static {
        /* ensure that the necessary native libraries are loaded */
        Toolkit.loadLibraries();
        if (!GraphicsEnvironment.isHeadless()) {
            initIDs();
        }
        AWTAccessor.setAWTEventAccessor(
            new AWTAccessor.AWTEventAccessor() {
                public void setPosted(AWTEvent ev) {
                    ev.isPosted = true;
                }

                public void setSystemGenerated(AWTEvent ev) {
                    ev.isSystemGenerated = true;
                }

                public boolean isSystemGenerated(AWTEvent ev) {
                    return ev.isSystemGenerated;
                }

                public AccessControlContext getAccessControlContext(AWTEvent ev) {
                    return ev.getAccessControlContext();
                }

                public byte[] getBData(AWTEvent ev) {
                    return ev.bdata;
                }

                public void setBData(AWTEvent ev, byte[] bdata) {
                    ev.bdata = bdata;
                }

            });
    }

    private static synchronized Field get_InputEvent_CanAccessSystemClipboard() {
        if (inputEvent_CanAccessSystemClipboard_Field == null) {
            inputEvent_CanAccessSystemClipboard_Field =
                (Field)java.security.AccessController.doPrivileged(
                    new java.security.PrivilegedAction() {
                            public Object run() {
                                Field field = null;
                                try {
                                    field = InputEvent.class.
                                        getDeclaredField("canAccessSystemClipboard");
                                    field.setAccessible(true);
                                    return field;
                                } catch (SecurityException e) {
                                    if (log.isLoggable(PlatformLogger.FINE)) {
                                        log.fine("AWTEvent.get_InputEvent_CanAccessSystemClipboard() got SecurityException ", e);
                                    }
                                } catch (NoSuchFieldException e) {
                                    if (log.isLoggable(PlatformLogger.FINE)) {
                                        log.fine("AWTEvent.get_InputEvent_CanAccessSystemClipboard() got NoSuchFieldException ", e);
                                    }
                                }
                                return null;
                            }
                        });
        }

        return inputEvent_CanAccessSystemClipboard_Field;
    }

    /**
     * Initialize JNI field and method IDs for fields that may be
     * accessed from C.
     */
    private static native void initIDs();

    /**
     * Constructs an AWTEvent object from the parameters of a 1.0-style event.
     * @param event the old-style event
     */
    public AWTEvent(Event event) {
        this(event.target, event.id);
    }

    /**
     * Constructs an AWTEvent object with the specified source object and type.
     *
     * @param source the object where the event originated
     * @param id the event type
     */
    public AWTEvent(Object source, int id) {
        super(source);
        this.id = id;
        switch(id) {
          case ActionEvent.ACTION_PERFORMED:
          case ItemEvent.ITEM_STATE_CHANGED:
          case AdjustmentEvent.ADJUSTMENT_VALUE_CHANGED:
          case TextEvent.TEXT_VALUE_CHANGED:
            consumed = true;
            break;
          default:
        }
    }

    /**
     * Retargets an event to a new source. This method is typically used to
     * retarget an event to a lightweight child Component of the original
     * heavyweight source.
     * <p>
     * This method is intended to be used only by event targeting subsystems,
     * such as client-defined KeyboardFocusManagers. It is not for general
     * client use.
     *
     * @param newSource the new Object to which the event should be dispatched
     * @since 1.4
     */
    public void setSource(Object newSource) {
        if (source == newSource) {
            return;
        }

        Component comp = null;
        if (newSource instanceof Component) {
            comp = (Component)newSource;
            while (comp != null && comp.peer != null &&
                   (comp.peer instanceof LightweightPeer)) {
                comp = comp.parent;
            }
        }

        synchronized (this) {
            source = newSource;
            if (comp != null) {
                ComponentPeer peer = comp.peer;
                if (peer != null) {
                    nativeSetSource(peer);
                }
            }
        }
    }

    private native void nativeSetSource(ComponentPeer peer);

    /**
     * Returns the event type.
     */
    public int getID() {
        return id;
    }

    /**
     * Returns a String representation of this object.
     */
    public String toString() {
        String srcName = null;
        if (source instanceof Component) {
            srcName = ((Component)source).getName();
        } else if (source instanceof MenuComponent) {
            srcName = ((MenuComponent)source).getName();
        }
        return getClass().getName() + "[" + paramString() + "] on " +
            (srcName != null? srcName : source);
    }

    /**
     * Returns a string representing the state of this <code>Event</code>.
     * 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
     * <code>null</code>.
     *
     * @return  a string representation of this event
     */
    public String paramString() {
        return "";
    }

    /**
     * Consumes this event, if this event can be consumed. Only low-level,
     * system events can be consumed
     */
    protected void consume() {
        switch(id) {
          case KeyEvent.KEY_PRESSED:
          case KeyEvent.KEY_RELEASED:
          case MouseEvent.MOUSE_PRESSED:
          case MouseEvent.MOUSE_RELEASED:
          case MouseEvent.MOUSE_MOVED:
          case MouseEvent.MOUSE_DRAGGED:
          case MouseEvent.MOUSE_ENTERED:
          case MouseEvent.MOUSE_EXITED:
          case MouseEvent.MOUSE_WHEEL:
          case InputMethodEvent.INPUT_METHOD_TEXT_CHANGED:
          case InputMethodEvent.CARET_POSITION_CHANGED:
              consumed = true;
              break;
          default:
              // event type cannot be consumed
        }
    }

    /**
     * Returns whether this event has been consumed.
     */
    protected boolean isConsumed() {
        return consumed;
    }

    /**
     * Converts a new event to an old one (used for compatibility).
     * If the new event cannot be converted (because no old equivalent
     * exists) then this returns null.
     *
     * Note: this method is here instead of in each individual new
     * event class in java.awt.event because we don't want to make
     * it public and it needs to be called from java.awt.
     */
    Event convertToOld() {
        Object src = getSource();
        int newid = id;

        switch(id) {
          case KeyEvent.KEY_PRESSED:
          case KeyEvent.KEY_RELEASED:
              KeyEvent ke = (KeyEvent)this;
              if (ke.isActionKey()) {
                  newid = (id == KeyEvent.KEY_PRESSED?
                           Event.KEY_ACTION : Event.KEY_ACTION_RELEASE);
              }
              int keyCode = ke.getKeyCode();
              if (keyCode == KeyEvent.VK_SHIFT ||
                  keyCode == KeyEvent.VK_CONTROL ||
                  keyCode == KeyEvent.VK_ALT) {
                  return null;  // suppress modifier keys in old event model.
              }
              // no mask for button1 existed in old Event - strip it out
              return new Event(src, ke.getWhen(), newid, 0, 0,
                               Event.getOldEventKey(ke),
                               (ke.getModifiers() & ~InputEvent.BUTTON1_MASK));

          case MouseEvent.MOUSE_PRESSED:
          case MouseEvent.MOUSE_RELEASED:
          case MouseEvent.MOUSE_MOVED:
          case MouseEvent.MOUSE_DRAGGED:
          case MouseEvent.MOUSE_ENTERED:
          case MouseEvent.MOUSE_EXITED:
              MouseEvent me = (MouseEvent)this;
              // no mask for button1 existed in old Event - strip it out
              Event olde = new Event(src, me.getWhen(), newid,
                               me.getX(), me.getY(), 0,
                               (me.getModifiers() & ~InputEvent.BUTTON1_MASK));
              olde.clickCount = me.getClickCount();
              return olde;

          case FocusEvent.FOCUS_GAINED:
              return new Event(src, Event.GOT_FOCUS, null);

          case FocusEvent.FOCUS_LOST:
              return new Event(src, Event.LOST_FOCUS, null);

          case WindowEvent.WINDOW_CLOSING:
          case WindowEvent.WINDOW_ICONIFIED:
          case WindowEvent.WINDOW_DEICONIFIED:
              return new Event(src, newid, null);

          case ComponentEvent.COMPONENT_MOVED:
              if (src instanceof Frame || src instanceof Dialog) {
                  Point p = ((Component)src).getLocation();
                  return new Event(src, 0, Event.WINDOW_MOVED, p.x, p.y, 0, 0);
              }
              break;

          case ActionEvent.ACTION_PERFORMED:
              ActionEvent ae = (ActionEvent)this;
              String cmd;
              if (src instanceof Button) {
                  cmd = ((Button)src).getLabel();
              } else if (src instanceof MenuItem) {
                  cmd = ((MenuItem)src).getLabel();
              } else {
                  cmd = ae.getActionCommand();
              }
              return new Event(src, 0, newid, 0, 0, 0, ae.getModifiers(), cmd);

          case ItemEvent.ITEM_STATE_CHANGED:
              ItemEvent ie = (ItemEvent)this;
              Object arg;
              if (src instanceof List) {
                  newid = (ie.getStateChange() == ItemEvent.SELECTED?
                           Event.LIST_SELECT : Event.LIST_DESELECT);
                  arg = ie.getItem();
              } else {
                  newid = Event.ACTION_EVENT;
                  if (src instanceof Choice) {
                      arg = ie.getItem();

                  } else { // Checkbox
                      arg = Boolean.valueOf(ie.getStateChange() == ItemEvent.SELECTED);
                  }
              }
              return new Event(src, newid, arg);

          case AdjustmentEvent.ADJUSTMENT_VALUE_CHANGED:
              AdjustmentEvent aje = (AdjustmentEvent)this;
              switch(aje.getAdjustmentType()) {
                case AdjustmentEvent.UNIT_INCREMENT:
                  newid = Event.SCROLL_LINE_DOWN;
                  break;
                case AdjustmentEvent.UNIT_DECREMENT:
                  newid = Event.SCROLL_LINE_UP;
                  break;
                case AdjustmentEvent.BLOCK_INCREMENT:
                  newid = Event.SCROLL_PAGE_DOWN;
                  break;
                case AdjustmentEvent.BLOCK_DECREMENT:
                  newid = Event.SCROLL_PAGE_UP;
                  break;
                case AdjustmentEvent.TRACK:
                  if (aje.getValueIsAdjusting()) {
                      newid = Event.SCROLL_ABSOLUTE;
                  }
                  else {
                      newid = Event.SCROLL_END;
                  }
                  break;
                default:
                  return null;
              }
              return new Event(src, newid, Integer.valueOf(aje.getValue()));

          default:
        }
        return null;
    }

    /**
     * Copies all private data from this event into that.
     * Space is allocated for the copied data that will be
     * freed when the that is finalized. Upon completion,
     * this event is not changed.
     */
    void copyPrivateDataInto(AWTEvent that) {
        that.bdata = this.bdata;
        // Copy canAccessSystemClipboard value from this into that.
        if (this instanceof InputEvent && that instanceof InputEvent) {
            Field field = get_InputEvent_CanAccessSystemClipboard();
            if (field != null) {
                try {
                    boolean b = field.getBoolean(this);
                    field.setBoolean(that, b);
                } catch(IllegalAccessException e) {
                    if (log.isLoggable(PlatformLogger.FINE)) {
                        log.fine("AWTEvent.copyPrivateDataInto() got IllegalAccessException ", e);
                    }
                }
            }
        }
        that.isSystemGenerated = this.isSystemGenerated;
    }

    void dispatched() {
        if (this instanceof InputEvent) {
            Field field = get_InputEvent_CanAccessSystemClipboard();
            if (field != null) {
                try {
                    field.setBoolean(this, false);
                } catch(IllegalAccessException e) {
                    if (log.isLoggable(PlatformLogger.FINE)) {
                        log.fine("AWTEvent.dispatched() got IllegalAccessException ", e);
                    }
                }
            }
        }
    }
} // class AWTEvent

-------------------------------------------

看看监听器吧。

package java.awt.event;

import java.util.EventListener;

/**
 * The listener interface for receiving action events.
 * The class that is interested in processing an action event
 * implements this interface, and the object created with that
 * class is registered with a component, using the component's
 * <code>addActionListener</code> method. When the action event
 * occurs, that object's <code>actionPerformed</code> method is
 * invoked.
 *
 * @see ActionEvent
 * @see <a href="http://java.sun.com/docs/books/tutorial/post1.0/ui/eventmodel.html">Tutorial: Java 1.1 Event Model</a>
 *
 * @author Carl Quinn
 * @since 1.1
 */
public interface ActionListener extends EventListener {//注意EventListener这是一个标记接口，同有java.io.Serializable接口也是标记接口

    /**
     * Invoked when an action occurs.
     */
    public void actionPerformed(ActionEvent e);//这个方法是子接口定义的。

}

---------------------------------------

最后我们来看看事件源类吧。图形化编程中很很多,AWT,SWING中。找个最常见的，简单的。Button.java

public class Button extends Component implements Accessible {

.....

 /**
     * The action to be performed once a button has been
     * pressed.  This value may be null.
     * @serial
     * @see #getActionCommand()
     * @see #setActionCommand(String)
     */
    String actionCommand;

    transient ActionListener actionListener;

......

 public synchronized void addActionListener(ActionListener l) {
        if (l == null) {
            return;
        }
        actionListener = AWTEventMulticaster.add(actionListener, l);
        newEventsOnly = true;
    }

..............

 public synchronized void removeActionListener(ActionListener l) {
        if (l == null) {
            return;
        }
        actionListener = AWTEventMulticaster.remove(actionListener, l);
    }

....

中间好多代码省略了，因为那不是我们关心的。

---------------------------

看到这文章有用，就请回复一下，谢谢。