1 |
771 |
jeremybenn |
/* Observable.java -- an object to be observed
|
2 |
|
|
Copyright (C) 1999, 2000, 2001, 2002, 2005 Free Software Foundation, Inc.
|
3 |
|
|
|
4 |
|
|
This file is part of GNU Classpath.
|
5 |
|
|
|
6 |
|
|
GNU Classpath is free software; you can redistribute it and/or modify
|
7 |
|
|
it under the terms of the GNU General Public License as published by
|
8 |
|
|
the Free Software Foundation; either version 2, or (at your option)
|
9 |
|
|
any later version.
|
10 |
|
|
|
11 |
|
|
GNU Classpath is distributed in the hope that it will be useful, but
|
12 |
|
|
WITHOUT ANY WARRANTY; without even the implied warranty of
|
13 |
|
|
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
|
14 |
|
|
General Public License for more details.
|
15 |
|
|
|
16 |
|
|
You should have received a copy of the GNU General Public License
|
17 |
|
|
along with GNU Classpath; see the file COPYING. If not, write to the
|
18 |
|
|
Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
|
19 |
|
|
02110-1301 USA.
|
20 |
|
|
|
21 |
|
|
Linking this library statically or dynamically with other modules is
|
22 |
|
|
making a combined work based on this library. Thus, the terms and
|
23 |
|
|
conditions of the GNU General Public License cover the whole
|
24 |
|
|
combination.
|
25 |
|
|
|
26 |
|
|
As a special exception, the copyright holders of this library give you
|
27 |
|
|
permission to link this library with independent modules to produce an
|
28 |
|
|
executable, regardless of the license terms of these independent
|
29 |
|
|
modules, and to copy and distribute the resulting executable under
|
30 |
|
|
terms of your choice, provided that you also meet, for each linked
|
31 |
|
|
independent module, the terms and conditions of the license of that
|
32 |
|
|
module. An independent module is a module which is not derived from
|
33 |
|
|
or based on this library. If you modify this library, you may extend
|
34 |
|
|
this exception to your version of the library, but you are not
|
35 |
|
|
obligated to do so. If you do not wish to do so, delete this
|
36 |
|
|
exception statement from your version. */
|
37 |
|
|
|
38 |
|
|
|
39 |
|
|
package java.util;
|
40 |
|
|
|
41 |
|
|
/**
|
42 |
|
|
* This class represents an object which is observable. Other objects may
|
43 |
|
|
* register their intent to be notified when this object changes; and when
|
44 |
|
|
* this object does change, it will trigger the <code>update</code> method
|
45 |
|
|
* of each observer.
|
46 |
|
|
*
|
47 |
|
|
* Note that the <code>notifyObservers()</code> method of this class is
|
48 |
|
|
* unrelated to the <code>notify()</code> of Object.
|
49 |
|
|
*
|
50 |
|
|
* @author Warren Levy (warrenl@cygnus.com)
|
51 |
|
|
* @author Eric Blake (ebb9@email.byu.edu)
|
52 |
|
|
* @see Observer
|
53 |
|
|
* @status updated to 1.4
|
54 |
|
|
*/
|
55 |
|
|
public class Observable
|
56 |
|
|
{
|
57 |
|
|
/** Tracks whether this object has changed. */
|
58 |
|
|
private boolean changed;
|
59 |
|
|
|
60 |
|
|
/* List of the Observers registered as interested in this Observable. */
|
61 |
|
|
private LinkedHashSet observers;
|
62 |
|
|
|
63 |
|
|
/**
|
64 |
|
|
* Constructs an Observable with zero Observers.
|
65 |
|
|
*/
|
66 |
|
|
public Observable()
|
67 |
|
|
{
|
68 |
|
|
observers = new LinkedHashSet();
|
69 |
|
|
}
|
70 |
|
|
|
71 |
|
|
/**
|
72 |
|
|
* Adds an Observer. If the observer was already added this method does
|
73 |
|
|
* nothing.
|
74 |
|
|
*
|
75 |
|
|
* @param observer Observer to add
|
76 |
|
|
* @throws NullPointerException if observer is null
|
77 |
|
|
*/
|
78 |
|
|
public synchronized void addObserver(Observer observer)
|
79 |
|
|
{
|
80 |
|
|
if (observer == null)
|
81 |
|
|
throw new NullPointerException("can't add null observer");
|
82 |
|
|
observers.add(observer);
|
83 |
|
|
}
|
84 |
|
|
|
85 |
|
|
/**
|
86 |
|
|
* Reset this Observable's state to unchanged. This is called automatically
|
87 |
|
|
* by <code>notifyObservers</code> once all observers have been notified.
|
88 |
|
|
*
|
89 |
|
|
* @see #notifyObservers()
|
90 |
|
|
*/
|
91 |
|
|
protected synchronized void clearChanged()
|
92 |
|
|
{
|
93 |
|
|
changed = false;
|
94 |
|
|
}
|
95 |
|
|
|
96 |
|
|
/**
|
97 |
|
|
* Returns the number of observers for this object.
|
98 |
|
|
*
|
99 |
|
|
* @return number of Observers for this
|
100 |
|
|
*/
|
101 |
|
|
public synchronized int countObservers()
|
102 |
|
|
{
|
103 |
|
|
return observers.size();
|
104 |
|
|
}
|
105 |
|
|
|
106 |
|
|
/**
|
107 |
|
|
* Deletes an Observer of this Observable.
|
108 |
|
|
*
|
109 |
|
|
* @param victim Observer to delete
|
110 |
|
|
*/
|
111 |
|
|
public synchronized void deleteObserver(Observer victim)
|
112 |
|
|
{
|
113 |
|
|
observers.remove(victim);
|
114 |
|
|
}
|
115 |
|
|
|
116 |
|
|
/**
|
117 |
|
|
* Deletes all Observers of this Observable.
|
118 |
|
|
*/
|
119 |
|
|
public synchronized void deleteObservers()
|
120 |
|
|
{
|
121 |
|
|
observers.clear();
|
122 |
|
|
}
|
123 |
|
|
|
124 |
|
|
/**
|
125 |
|
|
* True if <code>setChanged</code> has been called more recently than
|
126 |
|
|
* <code>clearChanged</code>.
|
127 |
|
|
*
|
128 |
|
|
* @return whether or not this Observable has changed
|
129 |
|
|
*/
|
130 |
|
|
public synchronized boolean hasChanged()
|
131 |
|
|
{
|
132 |
|
|
return changed;
|
133 |
|
|
}
|
134 |
|
|
|
135 |
|
|
/**
|
136 |
|
|
* If the Observable has actually changed then tell all Observers about it,
|
137 |
|
|
* then reset state to unchanged.
|
138 |
|
|
*
|
139 |
|
|
* @see #notifyObservers(Object)
|
140 |
|
|
* @see Observer#update(Observable, Object)
|
141 |
|
|
*/
|
142 |
|
|
public void notifyObservers()
|
143 |
|
|
{
|
144 |
|
|
notifyObservers(null);
|
145 |
|
|
}
|
146 |
|
|
|
147 |
|
|
/**
|
148 |
|
|
* If the Observable has actually changed then tell all Observers about it,
|
149 |
|
|
* then reset state to unchanged. Note that though the order of
|
150 |
|
|
* notification is unspecified in subclasses, in Observable it is in the
|
151 |
|
|
* order of registration.
|
152 |
|
|
*
|
153 |
|
|
* @param obj argument to Observer's update method
|
154 |
|
|
* @see Observer#update(Observable, Object)
|
155 |
|
|
*/
|
156 |
|
|
public void notifyObservers(Object obj)
|
157 |
|
|
{
|
158 |
|
|
if (! hasChanged())
|
159 |
|
|
return;
|
160 |
|
|
// Create clone inside monitor, as that is relatively fast and still
|
161 |
|
|
// important to keep threadsafe, but update observers outside of the
|
162 |
|
|
// lock since update() can call arbitrary code.
|
163 |
|
|
Set s;
|
164 |
|
|
synchronized (this)
|
165 |
|
|
{
|
166 |
|
|
s = (Set) observers.clone();
|
167 |
|
|
}
|
168 |
|
|
int i = s.size();
|
169 |
|
|
Iterator iter = s.iterator();
|
170 |
|
|
while (--i >= 0)
|
171 |
|
|
((Observer) iter.next()).update(this, obj);
|
172 |
|
|
clearChanged();
|
173 |
|
|
}
|
174 |
|
|
|
175 |
|
|
/**
|
176 |
|
|
* Marks this Observable as having changed.
|
177 |
|
|
*/
|
178 |
|
|
protected synchronized void setChanged()
|
179 |
|
|
{
|
180 |
|
|
changed = true;
|
181 |
|
|
}
|
182 |
|
|
}
|