ListenerList


1   /*******************************************************************************
2    * Copyright (c) 2000, 2005 IBM Corporation and others.
3    * All rights reserved. This program and the accompanying materials
4    * are made available under the terms of the Eclipse Public License v1.0
5    * which accompanies this distribution, and is available at
6    * http://www.eclipse.org/legal/epl-v10.html
7    * 
8    * Contributors:
9    *     IBM Corporation - initial API and implementation
10   *******************************************************************************/
11  package org.eclipse.jdt.internal.launching;
12  
13  
14  /**
15   * Local version of org.eclipse.jface.util.ListenerList (modified)s
16   */
17  public class ListenerList {
18      /**
19       * The current number of listeners.
20       * Maintains invariant: 0 <= fSize <= listeners.length.
21       */
22      private int fSize;
23  
24      /**
25       * The list of listeners.  Initially <code>null</code> but initialized
26       * to an array of size capacity the first time a listener is added.
27       * Maintains invariant: listeners != null if and only if fSize != 0
28       */
29      private Object  [] fListeners= null;
30  
31      /**
32       * The empty array singleton instance, returned by getListeners()
33       * when size == 0.
34       */
35      private static final Object  [] EmptyArray= new Object  [0];
36  
37      /**
38       * Creates a listener list with the given initial capacity.
39       *
40       * @param capacity the number of listeners which this list can initially accept 
41       *    without growing its internal representation; must be at least 1
42       */
43      public ListenerList(int capacity) {
44          if (capacity < 1) {
45              throw new IllegalArgumentException  ();
46          }
47          fListeners= new Object  [capacity];
48          fSize= 0;
49      }
50  
51      /**
52       * Adds a listener to the list.
53       * Has no effect if an identical listener is already registered.
54       *
55       * @param listener a listener
56       */
57      public synchronized void add(Object   listener) {
58          if (listener == null) {
59              throw new IllegalArgumentException  ();
60          }
61          // check for duplicates using identity
62          for (int i= 0; i < fSize; ++i) {
63              if (fListeners[i] == listener) {
64                  return;
65              }
66          }
67          // grow array if necessary
68          if (fSize == fListeners.length) {
69              Object  [] temp= new Object  [(fSize * 2) + 1];
70              System.arraycopy(fListeners, 0, temp, 0, fSize);
71              fListeners= temp;
72          }
73          fListeners[fSize++]= listener;
74      }
75  
76      /**
77       * Returns an array containing all the registered listeners.
78       * The resulting array is unaffected by subsequent adds or removes.
79       * If there are no listeners registered, the result is an empty array
80       * singleton instance (no garbage is created).
81       * Use this method when notifying listeners, so that any modifications
82       * to the listener list during the notification will have no effect on the
83       * notification itself.
84       */
85      public synchronized Object  [] getListeners() {
86          if (fSize == 0) {
87              return EmptyArray;
88          }
89          Object  [] result= new Object  [fSize];
90          System.arraycopy(fListeners, 0, result, 0, fSize);
91          return result;
92      }
93  
94      /**
95       * Removes a listener from the list.
96       * Has no effect if an identical listener was not already registered.
97       *
98       * @param listener a listener
99       */
100     public synchronized void remove(Object   listener) {
101         if (listener == null) {
102             throw new IllegalArgumentException  ();
103         }
104 
105         for (int i= 0; i < fSize; ++i) {
106             if (fListeners[i] == listener) {
107                 if (--fSize == 0) {
108                     fListeners= new Object  [1];
109                 } else {
110                     if (i < fSize) {
111                         fListeners[i]= fListeners[fSize];
112                     }
113                     fListeners[fSize]= null;
114                 }
115                 return;
116             }
117         }
118     }
119 
120     /**
121      * Removes all the listeners from the list.
122      */
123     public void removeAll() {
124         fListeners= new Object  [0];
125         fSize= 0;
126     }
127 
128     /**
129      * Returns the number of registered listeners
130      *
131      * @return the number of registered listeners
132      */
133     public int size() {
134         return fSize;
135     }
136 }
137 
138
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