ListenerList


1   /*******************************************************************************
2    * Copyright (c) 2000, 2004 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.ltk.internal.core.refactoring;
12  
13  /**
14   * Local copy of org.eclipse.jface.ListenerList
15   */
16  public class ListenerList {
17  
18      static {
19          //XXX: 1GCQD0A: ITPVCM:WIN2000 - ListenerList should be part of a core project
20      }
21      
22      /**
23       * The initial capacity of the list. Always >= 1.
24       */
25      private int capacity;
26  
27      /**
28       * The current number of listeners.
29       * Maintains invariant: 0 <= size <= listeners.length.
30       */
31      private int size;
32  
33      /**
34       * The list of listeners.  Initially <code>null</code> but initialized
35       * to an array of size capacity the first time a listener is added.
36       * Maintains invariant: listeners != null IFF size != 0
37       */
38      private Object  [] listeners= null;
39  
40      /**
41       * The empty array singleton instance, returned by getListeners()
42       * when size == 0.
43       */
44      private static final Object  [] EmptyArray= new Object  [0];
45      
46      /**
47       * Creates a listener list with an initial capacity of 3.
48       */
49      public ListenerList() {
50          this(3);
51      }
52      
53      /**
54       * Creates a listener list with the given initial capacity.
55       *
56       * @param cap the number of listeners which this list can initially accept 
57       *    without growing its internal representation; must be at least 1
58       */
59      public ListenerList(int cap) {
60          Assert.isTrue(cap >= 1);
61          this.capacity= cap;
62      }
63      
64      /**
65       * Adds the given listener to this list. Has no effect if an identical listener
66       * is already registered.
67       *
68       * @param listener the listener
69       */
70      public void add(Object   listener) {
71          Assert.isNotNull(listener);
72          if (size == 0) {
73              listeners= new Object  [capacity];
74          } else {
75              // check for duplicates using identity
76              for (int i= 0; i < size; ++i) {
77                  if (listeners[i] == listener) {
78                      return;
79                  }
80              }
81              // grow array if necessary
82              if (size == listeners.length) {
83                  System.arraycopy(listeners, 0, listeners= new Object  [size * 2 + 1], 0, size);
84              }
85          }
86          listeners[size++]= listener;
87      }
88      
89      /**
90       * Returns an array containing all the registered listeners.
91       * The resulting array is unaffected by subsequent adds or removes.
92       * If there are no listeners registered, the result is an empty array
93       * singleton instance (no garbage is created).
94       * Use this method when notifying listeners, so that any modifications
95       * to the listener list during the notification will have no effect on the
96       * notification itself.
97       *
98       * @return the list of registered listeners
99       */
100     public Object  [] getListeners() {
101         if (size == 0)
102             return EmptyArray;
103         Object  [] result= new Object  [size];
104         System.arraycopy(listeners, 0, result, 0, size);
105         return result;
106     }
107     
108     /**
109      * Returns whether this listener list is empty.
110      *
111      * @return <code>true</code> if there are no registered listeners, and
112      *   <code>false</code> otherwise
113      */
114     public boolean isEmpty() {
115         return size == 0;
116     }
117     
118     /**
119      * Removes the given listener from this list. Has no effect if an identical
120      * listener was not already registered.
121      *
122      * @param listener the listener
123      */
124     public void remove(Object   listener) {
125         Assert.isNotNull(listener);
126         for (int i= 0; i < size; ++i) {
127             if (listeners[i] == listener) {
128                 if (--size == 0) {
129                     listeners= new Object  [1];
130                 } else {
131                     if (i < size) {
132                         listeners[i]= listeners[size];
133                     }
134                     listeners[size]= null;
135                 }
136                 return;
137             }
138         }
139     }
140     
141     /**
142      * Returns the number of registered listeners.
143      *
144      * @return the number of registered listeners
145      */
146     public int size() {
147         return size;
148     }
149 }
150
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