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Java > Open Source Codes > org > apache > commons > el > EnumeratedMap


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55
56 package org.apache.commons.el;
57
58 import java.util.Collection JavaDoc;
59 import java.util.Enumeration JavaDoc;
60 import java.util.HashMap JavaDoc;
61 import java.util.Map JavaDoc;
62 import java.util.Set JavaDoc;
63
64 /**
65  *
66  * <p>This is a Map implementation driven by a data source that only
67  * provides an enumeration of keys and a getValue(key) method. This
68  * class must be subclassed to implement those methods.
69  *
70  * <p>Some of the methods may incur a performance penalty that
71  * involves enumerating the entire data source. In these cases, the
72  * Map will try to save the results of that enumeration, but only if
73  * the underlying data source is immutable.
74  *
75  * @author Nathan Abramson - Art Technology Group
76  * @version $Change: 181177 $$DateTime: 2001/06/26 08:45:09 $$Author: luehe $
77  **/
78
79 public abstract class EnumeratedMap
80   implements Map JavaDoc
81 {
82   //-------------------------------------
83 // Member variables
84 //-------------------------------------
85
86   Map JavaDoc mMap;
87
88   //-------------------------------------
89 public void clear ()
90   {
91     throw new UnsupportedOperationException JavaDoc ();
92   }
93
94   //-------------------------------------
95 public boolean containsKey (Object JavaDoc pKey)
96   {
97     return getValue (pKey) != null;
98   }
99
100   //-------------------------------------
101 public boolean containsValue (Object JavaDoc pValue)
102   {
103     return getAsMap ().containsValue (pValue);
104   }
105
106   //-------------------------------------
107 public Set JavaDoc entrySet ()
108   {
109     return getAsMap ().entrySet ();
110   }
111
112   //-------------------------------------
113 public Object JavaDoc get (Object JavaDoc pKey)
114   {
115     return getValue (pKey);
116   }
117
118   //-------------------------------------
119 public boolean isEmpty ()
120   {
121     return !enumerateKeys ().hasMoreElements ();
122   }
123
124   //-------------------------------------
125 public Set JavaDoc keySet ()
126   {
127     return getAsMap ().keySet ();
128   }
129
130   //-------------------------------------
131 public Object JavaDoc put (Object JavaDoc pKey, Object JavaDoc pValue)
132   {
133     throw new UnsupportedOperationException JavaDoc ();
134   }
135
136   //-------------------------------------
137 public void putAll (Map JavaDoc pMap)
138   {
139     throw new UnsupportedOperationException JavaDoc ();
140   }
141
142   //-------------------------------------
143 public Object JavaDoc remove (Object JavaDoc pKey)
144   {
145     throw new UnsupportedOperationException JavaDoc ();
146   }
147
148   //-------------------------------------
149 public int size ()
150   {
151     return getAsMap ().size ();
152   }
153
154   //-------------------------------------
155 public Collection JavaDoc values ()
156   {
157     return getAsMap ().values ();
158   }
159
160   //-------------------------------------
161 // Abstract methods
162 //-------------------------------------
163 /**
164    *
165    * Returns an enumeration of the keys
166    **/
167   public abstract Enumeration JavaDoc enumerateKeys ();
168
169   //-------------------------------------
170 /**
171    *
172    * Returns true if it is possible for this data source to change
173    **/
174   public abstract boolean isMutable ();
175
176   //-------------------------------------
177 /**
178    *
179    * Returns the value associated with the given key, or null if not
180    * found.
181    **/
182   public abstract Object JavaDoc getValue (Object JavaDoc pKey);
183
184   //-------------------------------------
185 /**
186    *
187    * Converts the MapSource to a Map. If the map is not mutable, this
188    * is cached
189    **/
190   public Map JavaDoc getAsMap ()
191   {
192     if (mMap != null) {
193       return mMap;
194     }
195     else {
196       Map JavaDoc m = convertToMap ();
197       if (!isMutable ()) {
198     mMap = m;
199       }
200       return m;
201     }
202   }
203
204   //-------------------------------------
205 /**
206    *
207    * Converts to a Map
208    **/
209   Map JavaDoc convertToMap ()
210   {
211     Map JavaDoc ret = new HashMap JavaDoc ();
212     for (Enumeration JavaDoc e = enumerateKeys (); e.hasMoreElements (); ) {
213       Object JavaDoc key = e.nextElement ();
214       Object JavaDoc value = getValue (key);
215       ret.put (key, value);
216     }
217     return ret;
218   }
219
220   //-------------------------------------
221 }
222
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