Iterators


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22  package org.jboss.util.collection;
23  
24  import java.util.Iterator  ;
25  import java.util.Enumeration  ;
26  import java.util.NoSuchElementException  ;
27  import java.util.Map  ;
28  import java.util.HashMap  ;
29  
30  import org.jboss.util.Null;
31  
32  /**
33   * A collection of <code>Iterator</code> and <code>Enumeration</code>
34   * utilities.
35   *
36   * @version <tt>$Revision: 1958 $</tt>
37   * @author  <a HREF="mailto:jason@planet57.com">Jason Dillon</a>
38   */
39  public final class Iterators
40  {
41     /////////////////////////////////////////////////////////////////////////
42     //                    Enumeration/Iterator Conversion                  //
43     /////////////////////////////////////////////////////////////////////////
44  
45     /**
46      * An Enumeration to Iterator wrapper.
47      */
48     private static final class Enum2Iterator
49        implements Iterator  
50     {
51        private final Enumeration   enumeration;
52      
53        public Enum2Iterator(final Enumeration   enumeration) {
54           this.enumeration = enumeration;
55        }
56     
57        public boolean hasNext() {
58           return enumeration.hasMoreElements();
59        }
60      
61        public Object   next() {
62           return enumeration.nextElement();
63        }
64        
65        public void remove() {
66           throw new UnsupportedOperationException  ("Enumerations are immutable");
67        }
68     }
69  
70     /**
71      * Return an Iterator wrapper for the given Enumeration
72      *
73      * @param enum    Enumeration to wrap
74      * @return        Enumeration wrapped as an Iterator
75      */
76     public static Iterator   forEnumeration(final Enumeration   enumeration) {
77        return new Enum2Iterator(enumeration);
78     }
79  
80     /**
81      * An Iterator to Enumeration wrapper class.
82      */
83     private static final class Iter2Enumeration
84        implements Enumeration  
85     {
86        private final Iterator   iter;
87  
88        public Iter2Enumeration(final Iterator   iter) {
89           this.iter = iter;
90        }
91  
92        public boolean hasMoreElements() {
93           return iter.hasNext();
94        }
95  
96        public Object   nextElement() {
97           return iter.next();
98        }
99     }
100 
101    /**
102     * Return an Enumeration for the given Iterator.
103     *
104     * @param iter    Iterator to wrap.
105     * @return        Enumeration wrapper.
106     */
107    public static Enumeration   toEnumeration(final Iterator   iter) {
108       return new Iter2Enumeration(iter);
109    }
110 
111 
112    /////////////////////////////////////////////////////////////////////////
113    //                           Iterator Wrappers                         //
114    /////////////////////////////////////////////////////////////////////////
115 
116    /**
117     * Wraps an Iterator making it immutable, by disabling calls to
118     * <code>remove()</code>
119     */
120    private static final class ImmutableIterator
121       implements Iterator  
122    {
123       private final Iterator   iter;
124 
125       public ImmutableIterator(final Iterator   iter) {
126          this.iter = iter;
127       }
128 
129       public boolean hasNext() {
130          return iter.hasNext();
131       }
132 
133       public Object   next() {
134          return iter.next();
135       }
136 
137       public void remove() {
138          throw new UnsupportedOperationException  ("iterator is immutable");
139       }
140    }
141 
142    /**
143     * Make an Iterator immutable
144     *
145     * @param iter    Iterator to make immutable
146     * @return        Imutable iterator
147     */
148    public static Iterator   makeImmutable(final Iterator   iter) {
149       return new ImmutableIterator(iter);
150    }
151 
152    /**
153     * Wraps an Iterator making it synchronized.
154     */
155    private static final class SyncIterator
156       implements Iterator  
157    {
158       private final Iterator   iter;
159 
160       public SyncIterator(final Iterator   iter) {
161          this.iter = iter;
162       }
163 
164       public synchronized boolean hasNext() {
165          return iter.hasNext();
166       }
167 
168       public synchronized Object   next() {
169          return iter.next();
170       }
171 
172       public synchronized void remove() {
173          iter.remove();
174       }
175    }
176 
177    /**
178     * Returns a synchronized version of the given Iterator.
179     *
180     * @param iter    Iterator to synchronize.
181     * @return        Synchronized Iterator.
182     */
183    public static Iterator   makeSynchronized(final Iterator   iter) {
184       return new SyncIterator(iter);
185    }
186 
187    /**
188     * Wraps an Enumeration making it synchronized.
189     */
190    private static final class SyncEnumeration
191       implements Enumeration  
192    {
193       private final Enumeration   enumeration;
194 
195       public SyncEnumeration(final Enumeration   enumeration) {
196          this.enumeration = enumeration;
197       }
198 
199       public synchronized boolean hasMoreElements() {
200          return enumeration.hasMoreElements();
201       }
202 
203       public synchronized Object   nextElement() {
204          return enumeration.nextElement();
205       }
206    }
207 
208    /**
209     * Returns a synchronized version of the given Enumeration.
210     *
211     * @param enum    Enumeration to synchronize.
212     * @return        Synchronized Enumeration.
213     */
214    public static Enumeration   makeSynchronized(final Enumeration   enumeration) {
215       return new SyncEnumeration(enumeration);
216    }
217 
218 
219    /////////////////////////////////////////////////////////////////////////
220    //                            Empty Iterator                           //
221    /////////////////////////////////////////////////////////////////////////
222 
223    /** An empty Iterator */
224    public static final Iterator   EMPTY_ITERATOR = new EmptyIterator();
225 
226    /**
227     * An empty Iterator
228     */
229    private static final class EmptyIterator
230       implements Iterator  
231    {
232       public boolean hasNext() {
233          return false;
234       }
235    
236       public Object   next() { 
237          throw new NoSuchElementException  ("no more elements");
238       }
239    
240       public void remove() {
241          throw new IllegalStateException  ("no more elements");
242       }
243    }
244 
245 
246    /////////////////////////////////////////////////////////////////////////
247    //                              Misc Methods                           //
248    /////////////////////////////////////////////////////////////////////////
249 
250    /**
251     * Returns an Iterator containing the <i>union</i> of all of the elements
252     * in the given iterator array.
253     *
254     * @param iters   Array of iterators.
255     * @return        Iterator containing the <i>union</i>.
256     */
257    public static Iterator   union(final Iterator   iters[]) {
258       Map   map = new HashMap  ();
259 
260       for (int i=0; i < iters.length; i++) {
261          if (iters[i] != null) {
262             while (iters[i].hasNext()) {
263                Object   obj = iters[i].next();
264                if (!map.containsKey(obj)) {
265                   map.put(obj, Null.VALUE);
266                }
267             }
268          }
269       }
270 
271       return map.keySet().iterator();
272    }
273 
274    /**
275     * Return a delimited string representation of all of the elements
276     * in the given Iterator.
277     *
278     * @param iter    Iterator to convert to string.
279     * @param delim   Elemement delimiter.
280     * @return        Delimited string value.
281     */
282    public static String   toString(final Iterator   iter, final String   delim) {
283       StringBuffer   buff = new StringBuffer  ();
284       while (iter.hasNext()) {
285          buff.append(iter.next());
286 
287          if (iter.hasNext()) {
288             buff.append(delim);
289          }
290       }
291 
292       return buff.toString();
293    }
294 
295    /**
296     * Return a comma delimited string representation of all of the elements
297     * in the given Iterator.
298     *
299     * @param iter    Iterator to convert to string.
300     * @return        Delimited string value.
301     */
302    public static String   toString(final Iterator   iter) {
303       return toString(iter, ",");
304    }
305 }
306
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