1 /*

     2  * Copyright 1997 Sun Microsystems, Inc.  All Rights Reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.  Sun designates this

     8  * particular file as subject to the "Classpath" exception as provided

     9  * by Sun in the LICENSE file that accompanied this code.

    10  *

    11  * This code is distributed in the hope that it will be useful, but WITHOUT

    12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    14  * version 2 for more details (a copy is included in the LICENSE file that

    15  * accompanied this code).

    16  *

    17  * You should have received a copy of the GNU General Public License version

    18  * 2 along with this work; if not, write to the Free Software Foundation,

    19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    20  *

    21  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

    22  * CA 95054 USA or visit www.sun.com if you need additional information or

    23  * have any questions.

    24  */

    25 

    26 package sun.applet;

    27 

    28 import java.util.EventListener;

    29 import java.io.Serializable;

    30 import java.io.ObjectOutputStream;

    31 import java.io.IOException;

    32 

    33 /**

    34  * AppletEventMulticaster class.  This class manages an immutable

    35  * structure consisting of a chain of AppletListeners and is

    36  * responsible for dispatching events to them.

    37  *

    38  * @author  Sunita Mani

    39  */

    40 public class AppletEventMulticaster implements AppletListener {

    41 

    42     private final AppletListener a, b;

    43 

    44     public AppletEventMulticaster(AppletListener a, AppletListener b) {

    45         this.a = a; this.b = b;

    46     }

    47 

    48     public void appletStateChanged(AppletEvent e) {

    49         a.appletStateChanged(e);

    50         b.appletStateChanged(e);

    51     }

    52 

    53     /**

    54      * Adds Applet-listener-a with Applet-listener-b and

    55      * returns the resulting multicast listener.

    56      * @param a Applet-listener-a

    57      * @param b Applet-listener-b

    58      */

    59     public static AppletListener add(AppletListener a, AppletListener b) {

    60         return addInternal(a, b);

    61     }

    62 

    63     /**

    64      * Removes the old Applet-listener from Applet-listener-l and

    65      * returns the resulting multicast listener.

    66      * @param l Applet-listener-l

    67      * @param oldl the Applet-listener being removed

    68      */

    69     public static AppletListener remove(AppletListener l, AppletListener oldl) {

    70         return removeInternal(l, oldl);

    71     }

    72 

    73     /**

    74      * Returns the resulting multicast listener from adding listener-a

    75      * and listener-b together.

    76      * If listener-a is null, it returns listener-b;

    77      * If listener-b is null, it returns listener-a

    78      * If neither are null, then it creates and returns

    79      * a new AppletEventMulticaster instance which chains a with b.

    80      * @param a event listener-a

    81      * @param b event listener-b

    82      */

    83     private static AppletListener addInternal(AppletListener a, AppletListener b) {

    84         if (a == null)  return b;

    85         if (b == null)  return a;

    86         return new AppletEventMulticaster(a, b);

    87     }

    88 

    89 

    90     /**

    91      * Removes a listener from this multicaster and returns the

    92      * resulting multicast listener.

    93      * @param oldl the listener to be removed

    94      */

    95     protected AppletListener remove(AppletListener oldl) {

    96         if (oldl == a)  return b;

    97         if (oldl == b)  return a;

    98         AppletListener a2 = removeInternal(a, oldl);

    99         AppletListener b2 = removeInternal(b, oldl);

   100         if (a2 == a && b2 == b) {

   101             return this;        // it's not here

   102         }

   103         return addInternal(a2, b2);

   104     }

   105 

   106 

   107     /**

   108      * Returns the resulting multicast listener after removing the

   109      * old listener from listener-l.

   110      * If listener-l equals the old listener OR listener-l is null,

   111      * returns null.

   112      * Else if listener-l is an instance of AppletEventMulticaster

   113      * then it removes the old listener from it.

   114      * Else, returns listener l.

   115      * @param l the listener being removed from

   116      * @param oldl the listener being removed

   117      */

   118     private static AppletListener removeInternal(AppletListener l, AppletListener oldl) {

   119         if (l == oldl || l == null) {

   120             return null;

   121         } else if (l instanceof AppletEventMulticaster) {

   122             return ((AppletEventMulticaster)l).remove(oldl);

   123         } else {

   124             return l;           // it's not here

   125         }

   126     }

   127 }