ReferenceCounter


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 Common Public License v1.0
5    * which accompanies this distribution, and is available at
6    * http://www.eclipse.org/legal/cpl-v10.html
7    * 
8    * Contributors:
9    *     IBM Corporation - initial API and implementation
10   *******************************************************************************/
11  package org.eclipse.team.internal.ui.synchronize;
12  
13  import java.util.*;
14  
15  /**
16   * A ReferenceCounter is used to reference counting objects.
17   * Each object is identified by a unique ID.  Together they form
18   * an ID - value pair. An object is added to the counter by calling
19   * #put(id, object).  From this point on additional refs can be made
20   * by calling #addRef(id) or #removeRef(id).
21   */
22  public class ReferenceCounter
23  {
24      private Map mapIdToRec = new HashMap(11);
25  
26      /**
27       * Capture the information about an object.
28       */
29      public class RefRec {
30          public RefRec(Object   id, Object   value) {
31              this.id = id;
32              this.value = value;
33              addRef();
34          }
35          public Object   getId() { 
36              return id;
37          }
38          public Object   getValue() { 
39              return value;
40          }
41          public int addRef() { 
42              ++ refCount;
43              return refCount;
44          }
45          public int removeRef() { 
46              -- refCount;
47              return refCount;
48          }
49          public int getRef() {
50              return refCount;
51          }
52          public boolean isNotReferenced() { 
53              return (refCount <= 0); 
54          }
55          public Object   id;
56          public Object   value;
57          private int refCount; 
58      }
59  /**
60   * Creates a new counter.
61   */
62  public ReferenceCounter() {
63      super();
64  }
65  /**
66   * Adds one reference to an object in the counter.
67   *
68   * @param id is a unique ID for the object.
69   * @return the new ref count
70   */
71  public int addRef(Object   id) {
72      RefRec rec = (RefRec)mapIdToRec.get(id);
73      if (rec == null)
74          return 0;
75      return rec.addRef();
76  }
77  /**
78   * Returns the object defined by an ID.  If the ID is not
79   * found <code>null</code> is returned.
80   *
81   * @return the object or <code>null</code>
82   */
83  public Object   get(Object   id) {
84      RefRec rec = (RefRec)mapIdToRec.get(id);
85      if (rec == null)
86          return null;
87      return rec.getValue();
88  }
89  /**
90   * Returns a complete list of the keys in the counter.
91   *
92   * @return a Set containing the ID for each.
93   */
94  public Set keySet() {
95      return mapIdToRec.keySet();
96  }
97  /**
98   * Adds an object to the counter for counting and gives
99   * it an initial ref count of 1.
100  *
101  * @param id is a unique ID for the object.
102  * @param value is the object itself.
103  */
104 public void put(Object   id, Object   value) {
105     RefRec rec = new RefRec(id, value);
106     mapIdToRec.put(id, rec);
107 }
108 /**
109  * Removes one reference from an object in the counter.
110  * If the ref count drops to 0 the object is removed from
111  * the counter completely.
112  *
113  * @param id is a unique ID for the object.
114  * @return the new ref count
115  */
116 public int removeRef(Object   id) {
117     RefRec rec = (RefRec)mapIdToRec.get(id);
118     if (rec == null)
119         return 0;
120     int newCount = rec.removeRef();
121     if (newCount <= 0)
122         mapIdToRec.remove(id);
123     return newCount;
124 }
125 /**
126  * Returns a complete list of the values in the counter.
127  *
128  * @return a Collection containing the values.
129  */
130 public List values() {
131     int size = mapIdToRec.size();
132     ArrayList list = new ArrayList(size);
133     Iterator iter = mapIdToRec.values().iterator();
134     while (iter.hasNext()) {
135         RefRec rec = (RefRec)iter.next();
136         list.add(rec.getValue());
137     }
138     return list;
139 }
140 }
141
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