1 /*
2 * Copyright (c) 1997, Oracle and/or its affiliates. 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. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * 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 }