Classes in this File | Line Coverage | Branch Coverage | Complexity | ||||||||
EOObserverCenter |
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| 2.8;2.8 |
1 | /* |
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2 | Wotonomy: OpenStep design patterns for pure Java applications. |
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3 | Copyright (C) 2000 Intersect Software Corporation |
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4 | ||
5 | This library is free software; you can redistribute it and/or |
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6 | modify it under the terms of the GNU Lesser General Public |
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7 | License as published by the Free Software Foundation; either |
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8 | version 2.1 of the License, or (at your option) any later version. |
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9 | ||
10 | This library is distributed in the hope that it will be useful, |
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11 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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12 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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13 | Lesser General Public License for more details. |
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14 | ||
15 | You should have received a copy of the GNU Lesser General Public |
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16 | License along with this library; if not, see http://www.gnu.org |
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17 | */ |
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18 | ||
19 | package net.wotonomy.control; |
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20 | ||
21 | import java.lang.ref.Reference; |
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22 | import java.lang.ref.ReferenceQueue; |
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23 | import java.lang.ref.WeakReference; |
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24 | import java.util.ArrayList; |
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25 | import java.util.Hashtable; |
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26 | import java.util.Iterator; |
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27 | import java.util.LinkedList; |
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28 | import java.util.List; |
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29 | import java.util.Map; |
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30 | import java.util.Observable; |
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31 | import java.util.Observer; |
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32 | ||
33 | import net.wotonomy.foundation.NSArray; |
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34 | import net.wotonomy.foundation.NSMutableArray; |
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35 | ||
36 | /** |
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37 | * EOObserverCenter is a static singleton-like class |
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38 | * that manages EOObservings that want to be notified |
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39 | * of changes to those objects that call |
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40 | * notifyObserversObjectWillChange() before their |
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41 | * properties change. <br><br> |
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42 | * |
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43 | * Implementation note: Because Java implements the |
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44 | * Observer pattern in java.util.Observable, this |
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45 | * class knows how to register itself as an Observer |
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46 | * with Observables as well. However, users should |
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47 | * note that Observables only notify their Observers |
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48 | * of changes after their property has changed. |
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49 | * EODelayedObservers would see no difference because |
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50 | * they always receive their notification after all |
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51 | * changes have taken place. <br><br> |
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52 | * |
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53 | * This implementation uses weak references for observers |
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54 | * and observables. The advantage to this approach is |
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55 | * that you do not need to explicitly unregister observers |
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56 | * or observables; they will be unregistered when they are |
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57 | * garbage-collected. Note that you will need to retain |
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58 | * a reference to any objects you register or they may |
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59 | * become unregistered if no other object references them. |
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60 | * |
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61 | * @author michael@mpowers.net |
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62 | * @author $Author: cgruber $ |
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63 | * @version $Revision: 894 $ |
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64 | */ |
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65 | 0 | public class EOObserverCenter implements Observer |
66 | { |
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67 | /** |
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68 | * Would much rather use a WeakHashMap, but that class |
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69 | * compares by value, and we need to compare by reference. |
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70 | * This means we need to recreate a weak hashmap with |
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71 | * the ReferenceKey class below. Using hashtable for |
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72 | * thread safety. |
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73 | */ |
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74 | 0 | private static Map observableToObservers = new Hashtable(); |
75 | ||
76 | 0 | private static List omniscients = new LinkedList(); |
77 | ||
78 | // suppression count |
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79 | 0 | private static int suppressions = 0; |
80 | ||
81 | // singleton instance - needed for Observer |
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82 | 0 | private static EOObserverCenter instance = null; |
83 | ||
84 | // optimization: remember last request and result |
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85 | private static Object lastRequest; |
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86 | private static NSArray lastResult; |
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87 | ||
88 | /** |
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89 | * Registers the specified EOObserving for |
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90 | * notifications from the specified object. |
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91 | * An EOObserving can only be registered |
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92 | * once for a given object. |
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93 | */ |
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94 | public static void addObserver( |
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95 | EOObserving anObserver, Object anObject ) |
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96 | { |
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97 | // atomic operation |
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98 | 0 | synchronized ( instance() ) |
99 | { |
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100 | // find observer list |
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101 | 0 | List observers = (List) |
102 | 0 | observableToObservers.get( new ReferenceKey( anObject ) ); |
103 | ||
104 | // if observer list not found, create and add item |
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105 | 0 | if ( observers == null ) |
106 | { |
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107 | 0 | observers = new ArrayList(); |
108 | 0 | observers.add( new WeakReference( anObserver ) ); |
109 | 0 | processQueue(); |
110 | 0 | observableToObservers.put( new ReferenceKey( anObject, queue ), observers ); |
111 | ||
112 | // support for java.util.Observable |
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113 | 0 | if ( anObject instanceof Observable ) |
114 | { |
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115 | 0 | ((Observable)anObject).addObserver( instance() ); |
116 | 0 | } |
117 | } |
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118 | else // observer list found - scan for observer |
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119 | 0 | if ( indexOf( observers, anObserver ) < 0 ) |
120 | { |
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121 | // observer not found, register it |
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122 | 0 | observers.add( new WeakReference( anObserver ) ); |
123 | } |
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124 | ||
125 | 0 | lastRequest = null; |
126 | 0 | lastResult = null; |
127 | 0 | } |
128 | 0 | } |
129 | ||
130 | /** |
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131 | * Registers the specified EOObserving for notifications |
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132 | * on all object changes. An EOObserving can be |
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133 | * registered as an omniscient observer at most once. |
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134 | * Use omniscient observers with caution. |
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135 | */ |
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136 | public static void addOmniscientObserver( |
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137 | EOObserving anObserver ) |
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138 | { |
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139 | 0 | if ( indexOf( omniscients, anObserver ) < 0 ) |
140 | { |
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141 | 0 | omniscients.add( anObserver ); |
142 | } |
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143 | 0 | } |
144 | ||
145 | /** |
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146 | * Notifies all EOObservings registered for |
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147 | * notifications for the specified object. |
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148 | * This method is typically called by objects |
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149 | * that wish to broadcast a notification before |
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150 | * a property change takes place, passing itself |
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151 | * as the argument. |
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152 | */ |
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153 | public static void notifyObserversObjectWillChange( |
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154 | Object anObject ) |
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155 | { |
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156 | 0 | if ( observerNotificationSuppressCount() == 0 ) |
157 | { |
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158 | 0 | List observers = observersForObject( anObject ); |
159 | EOObserving o; |
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160 | 0 | Iterator it = observers.iterator(); |
161 | 0 | while ( it.hasNext() ) |
162 | { |
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163 | 0 | o = (EOObserving) it.next(); |
164 | 0 | o.objectWillChange( anObject ); |
165 | 0 | } |
166 | } |
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167 | 0 | } |
168 | ||
169 | /** |
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170 | * Returns an observer that is an instance of |
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171 | * the specified class and |
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172 | * that is registered for notifications about |
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173 | * the specified object. If more than one |
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174 | * such observer exists, which observer is |
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175 | * returned is undetermined - use |
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176 | * observersForObject instead. If no observer |
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177 | * exists, returns null. |
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178 | */ |
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179 | public static EOObserving observerForObject( |
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180 | Object anObject, Class aClass ) |
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181 | { |
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182 | 0 | List result = observersForObject( anObject ); |
183 | 0 | if ( result.size() == 0 ) return null; |
184 | ||
185 | Object o; |
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186 | 0 | Iterator it = result.iterator(); |
187 | 0 | while ( it.hasNext() ) |
188 | { |
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189 | 0 | o = it.next(); |
190 | 0 | if ( aClass.isAssignableFrom( o.getClass() ) ) |
191 | { |
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192 | 0 | return (EOObserving) o; |
193 | } |
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194 | } |
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195 | 0 | return null; |
196 | } |
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197 | ||
198 | /** |
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199 | * Returns the number of times that notifications |
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200 | * have been suppressed. This is also the number |
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201 | * of times that enableObserverNotification must |
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202 | * be called to allow notifications to take place. |
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203 | */ |
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204 | public static int observerNotificationSuppressCount() |
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205 | { |
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206 | 0 | return suppressions; |
207 | } |
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208 | ||
209 | /** |
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210 | * Returns a List of observers for the |
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211 | * specified object. Returns an empty List |
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212 | * if no observer has registered for that |
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213 | * object. |
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214 | */ |
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215 | public static NSArray observersForObject( |
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216 | Object anObject ) |
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217 | { |
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218 | 0 | synchronized ( instance() ) |
219 | { |
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220 | // optimization: this is called very frequently |
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221 | // from the same object calling willChange() a |
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222 | // number of times in a row as it is updating. |
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223 | 0 | if ( lastRequest == anObject ) |
224 | { |
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225 | 0 | return lastResult; |
226 | } |
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227 | ||
228 | NSArray result; |
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229 | ||
230 | 0 | List references = observerListForObject( anObject ); |
231 | 0 | if ( references == null ) |
232 | { |
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233 | 0 | result = NSArray.EmptyArray; |
234 | 0 | } |
235 | else |
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236 | { |
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237 | 0 | result = new NSMutableArray(); |
238 | Object observer; |
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239 | 0 | Iterator it = references.iterator(); |
240 | 0 | while ( it.hasNext() ) |
241 | { |
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242 | 0 | observer = ((Reference)it.next()).get(); |
243 | 0 | if ( observer != null ) |
244 | { |
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245 | 0 | result.add( observer ); |
246 | 0 | } |
247 | else // reference has expired |
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248 | { |
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249 | 0 | processQueue(); |
250 | 0 | it.remove(); // remove from list |
251 | // if last observer, unregister observable |
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252 | 0 | if ( references.size() == 0 ) |
253 | { |
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254 | 0 | observableToObservers.remove( new ReferenceKey( anObject ) ); |
255 | 0 | } |
256 | } |
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257 | } |
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258 | } |
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259 | ||
260 | 0 | lastRequest = anObject; |
261 | 0 | lastResult = result; |
262 | ||
263 | 0 | return result; |
264 | 0 | } |
265 | ||
266 | } |
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267 | ||
268 | /** |
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269 | * Returns a reference to the actual list of |
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270 | * observers for the given object, or null if it |
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271 | * doesn't exist. |
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272 | */ |
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273 | private static List observerListForObject( Object anObject ) |
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274 | { |
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275 | 0 | return (List) observableToObservers.get( new ReferenceKey( anObject ) ); |
276 | } |
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277 | ||
278 | /** |
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279 | * Unregisters the specified observer for |
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280 | * notifications from the specified object. |
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281 | */ |
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282 | public static void removeObserver( |
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283 | EOObserving anObserver, Object anObject ) |
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284 | { |
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285 | // atomic operation |
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286 | 0 | synchronized ( instance() ) |
287 | { |
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288 | 0 | lastRequest = null; |
289 | 0 | lastResult = null; |
290 | ||
291 | 0 | List result = observerListForObject( anObject ); |
292 | 0 | if ( result == null ) return; |
293 | 0 | int index = indexOf( result, anObserver ); |
294 | 0 | if ( index == -1 ) return; |
295 | ||
296 | // remove observer from list |
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297 | 0 | result.remove( index ); |
298 | ||
299 | // if last observer, unregister observable |
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300 | 0 | if ( result.size() == 0 ) |
301 | { |
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302 | 0 | processQueue(); |
303 | 0 | observableToObservers.remove( new ReferenceKey( anObject ) ); |
304 | } |
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305 | 0 | } |
306 | 0 | } |
307 | ||
308 | /** |
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309 | * Unregisters the specified omniscient observer. |
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310 | */ |
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311 | public static void removeOmniscientObserver( |
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312 | EOObserving anObserver ) |
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313 | { |
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314 | 0 | int index = indexOf( omniscients, anObserver ); |
315 | 0 | if ( index != -1 ) |
316 | { |
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317 | 0 | omniscients.remove( index ); |
318 | } |
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319 | 0 | } |
320 | ||
321 | /** |
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322 | * Enables notifications after they have been |
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323 | * suppressed by suppressObserverNotification. |
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324 | * If notifications have been suppressed |
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325 | * multiple times, this method must be called |
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326 | * an equal number of times to resume notifications. |
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327 | * If notifications are not currently suppressed, |
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328 | * this method does nothing. |
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329 | */ |
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330 | public static void enableObserverNotification() |
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331 | { |
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332 | 0 | if ( suppressions > 0 ) suppressions--; |
333 | 0 | } |
334 | ||
335 | /** |
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336 | * Causes notifications to be suppressed until |
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337 | * the next matching call to enableObserverNotification. |
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338 | * If this method is called more than once, |
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339 | * enableObserverNotification must be called an |
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340 | * equal number of times for notifications to resume. |
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341 | * This method always causes notifications to cease |
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342 | * immediately. |
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343 | */ |
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344 | public static void suppressObserverNotification() |
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345 | { |
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346 | 0 | suppressions++; |
347 | 0 | } |
348 | ||
349 | /** |
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350 | * Because we're comparing by reference, we need to |
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351 | * test for the existence of the object directly. |
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352 | * @return the index or -1 if not found. |
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353 | */ |
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354 | private static int indexOf( List aList, Object anObject ) |
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355 | { |
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356 | 0 | if ( anObject == null ) return -1; |
357 | ||
358 | 0 | synchronized ( aList ) |
359 | { |
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360 | 0 | int len = aList.size(); |
361 | 0 | for ( int i = 0; i < len; i++ ) |
362 | { |
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363 | // compare by reference |
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364 | 0 | if ( anObject == ((Reference)aList.get(i)).get() ) |
365 | { |
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366 | 0 | return i; |
367 | } |
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368 | } |
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369 | 0 | } |
370 | 0 | return -1; |
371 | } |
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372 | ||
373 | /** |
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374 | * Private singleton instance, so we can be an observer. |
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375 | */ |
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376 | private static EOObserverCenter instance() |
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377 | { |
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378 | 0 | if ( instance == null ) |
379 | { |
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380 | 0 | instance = new EOObserverCenter(); |
381 | } |
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382 | 0 | return instance; |
383 | } |
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384 | ||
385 | /** |
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386 | * Interface Observer |
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387 | */ |
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388 | public void update( Observable o, Object arg ) |
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389 | { |
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390 | 0 | notifyObserversObjectWillChange( o ); |
391 | 0 | } |
392 | ||
393 | /* Reference queue for cleared WeakKeys */ |
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394 | 0 | private static ReferenceQueue queue = new ReferenceQueue(); |
395 | ||
396 | /* Remove all invalidated entries from the map, that is, remove all entries |
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397 | whose keys have been discarded. This method should be invoked once by |
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398 | each public mutator in this class. We don't invoke this method in |
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399 | public accessors because that can lead to surprising |
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400 | ConcurrentModificationExceptions. */ |
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401 | private static void processQueue() |
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402 | { |
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403 | 0 | synchronized ( instance() ) |
404 | { |
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405 | ReferenceKey rk; |
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406 | 0 | while ((rk = (ReferenceKey)queue.poll()) != null) |
407 | { |
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408 | //System.out.println( "EOObserverCenter.processQueue: removing object" ); |
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409 | 0 | observableToObservers.remove(rk); |
410 | 0 | } |
411 | 0 | } |
412 | 0 | } |
413 | ||
414 | /** |
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415 | * Private class used to force a hashmap to |
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416 | * perform key comparisons by reference. |
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417 | * Retains a weak reference just like WeakHashMap. |
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418 | */ |
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419 | 0 | static private class ReferenceKey extends WeakReference |
420 | { |
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421 | private int hashCode; |
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422 | ||
423 | /** |
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424 | * Called to create a disposable reference key, |
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425 | * used for retrieving values from the hashtable. |
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426 | */ |
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427 | public ReferenceKey( Object anObject ) |
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428 | { |
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429 | 0 | super( anObject ); |
430 | 0 | hashCode = anObject.hashCode(); |
431 | 0 | } |
432 | ||
433 | /** |
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434 | * Called to create a reference key that will be |
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435 | * used as a key in the hashtable, so we need the |
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436 | * reference queue to later remove the key from the |
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437 | * table when referred object is no longer in use. |
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438 | */ |
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439 | public ReferenceKey( Object anObject, ReferenceQueue aQueue ) |
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440 | { |
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441 | 0 | super( anObject, aQueue ); |
442 | 0 | hashCode = anObject.hashCode(); |
443 | 0 | } |
444 | ||
445 | /** |
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446 | * Passes through to actual key's hash code. |
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447 | */ |
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448 | public int hashCode() |
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449 | { |
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450 | 0 | return hashCode; |
451 | } |
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452 | ||
453 | /** |
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454 | * Compares by reference. |
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455 | */ |
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456 | public boolean equals( Object anObject ) |
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457 | { |
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458 | 0 | if ( ! ( anObject instanceof ReferenceKey ) ) return false; |
459 | 0 | Object key = get(); |
460 | 0 | if ( key == null ) return false; |
461 | 0 | return ( key == ((ReferenceKey)anObject).get() ); |
462 | } |
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463 | } |
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464 | ||
465 | private static String debugString() |
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466 | { |
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467 | 0 | String result = ""; |
468 | 0 | int count = 0; |
469 | 0 | synchronized ( instance() ) |
470 | { |
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471 | Object anObject; |
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472 | 0 | Iterator it = observableToObservers.keySet().iterator(); |
473 | 0 | while ( it.hasNext() ) |
474 | { |
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475 | 0 | result += ((Reference)it.next()).get() + " : "; |
476 | 0 | count++; |
477 | /* |
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478 | Iterator values = ((List)it.next()).iterator(); |
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479 | while ( values.hasNext() ) |
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480 | { |
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481 | anObject = ((Reference)values.next()).get(); |
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482 | if ( anObject != null ) |
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483 | { |
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484 | // if ( anObject instanceof net.wotonomy.ui.MasterDetailAssociation ) |
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485 | result += anObject.getClass().toString() + " : "; |
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486 | count++; |
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487 | } |
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488 | } |
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489 | */ |
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490 | 0 | } |
491 | 0 | result += "["+count+"]"; |
492 | 0 | } |
493 | 0 | return result; |
494 | } |
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495 | ||
496 | } |
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497 | ||
498 | /* |
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499 | * $Log$ |
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500 | * Revision 1.2 2006/02/16 16:47:14 cgruber |
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501 | * Move some classes in to "internal" packages and re-work imports, etc. |
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502 | * |
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503 | * Also use UnsupportedOperationExceptions where appropriate, instead of WotonomyExceptions. |
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504 | * |
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505 | * Revision 1.1 2006/02/16 13:19:57 cgruber |
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506 | * Check in all sources in eclipse-friendly maven-enabled packages. |
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507 | * |
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508 | * Revision 1.9 2002/10/24 18:18:12 mpowers |
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509 | * NSArray's are now considered read-only, so we can return our internal |
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510 | * representation to reduce unnecessary object allocation. |
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511 | * |
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512 | * Revision 1.8 2001/02/21 21:17:32 mpowers |
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513 | * Now retaining a reference to the recent changes observer. |
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514 | * Better documented need to retain reference. |
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515 | * Started implementing notifications. |
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516 | * |
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517 | * Revision 1.7 2001/02/17 16:52:05 mpowers |
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518 | * Changes in imports to support building with jdk1.1 collections. |
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519 | * |
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520 | * Revision 1.6 2001/02/05 18:45:45 mpowers |
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521 | * Reduced access back to private for utility methods. |
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522 | * |
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523 | * Revision 1.5 2001/02/05 18:42:32 mpowers |
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524 | * Updated documentation throughout project. |
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525 | * |
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526 | * Revision 1.4 2001/01/18 16:57:47 mpowers |
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527 | * Added debug facility. |
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528 | * |
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529 | * Revision 1.3 2001/01/10 16:28:53 mpowers |
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530 | * Implemented a compare-by-reference weak hashtable |
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531 | * because WeakHashMap compared by value and we can't |
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532 | * assume that display groups won't contain objects |
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533 | * whose values are equivalent. |
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534 | * |
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535 | * Revision 1.2 2001/01/09 20:10:19 mpowers |
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536 | * Now using weak references to track observables and their observers. |
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537 | * |
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538 | * Revision 1.1.1.1 2000/12/21 15:46:44 mpowers |
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539 | * Contributing wotonomy. |
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540 | * |
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541 | * Revision 1.8 2000/12/20 16:25:35 michael |
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542 | * Added log to all files. |
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543 | * |
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544 | * |
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545 | */ |
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546 | ||
547 |