SmartIterator


1   package org.bsf.smartValueObject.container;
2   
3   import org.bsf.smartValueObject.VersionableFilter;
4   import org.bsf.smartValueObject.Versionable;
5   
6   import java.util.*;
7   
8   /**
9    * A replacement for <tt>java.util.Iterator</tt>.
10   * <p>This iterator respects the state of versionable objects,
11   * as they can be marked 'deleted' and should not be given out
12   * by an interator. It is configured via an <tt>VersionableFilter</tt>.
13   *
14   * @see org.bsf.smartValueObject.container.SmartCollection
15   * @see org.bsf.smartValueObject.container.SmartMap
16   * @see org.bsf.smartValueObject.VersionableFilter
17   */
18  public class SmartIterator implements Iterator {
19      /** Marker object as placeholder. */
20      private static final Object   NOOBJECT = new Object  ();
21      /** The underlying iterator. */
22      private Iterator it;
23      private Object   next = NOOBJECT;
24      /** This filter decides which objects are visible to the user. */
25      private VersionableFilter filter;
26  
27      /**
28       * Initializes this iterator with another iterator and
29       * a <tt>VersionableFilter</tt>.
30       *
31       * @param it the underlying iterator.
32       * @param f the filter to use while iterating.
33       */
34      public SmartIterator(Iterator it, VersionableFilter f) {
35          this.it = it;
36          this.filter = f;
37      }
38  
39      public boolean hasNext() {
40         while (it.hasNext()) {
41             next = it.next();
42             if (next instanceof Versionable) {
43                 if (!filter.accept((Versionable)next)) {
44                     // skip filtered objects
45                     continue;
46                 } else {
47                     return true;
48                 }
49             } else {
50                 // no versionable Object found
51                 continue;
52             }
53         }
54         return false;
55      }
56  
57      public Object   next() {
58          if (next == NOOBJECT) {
59              if (!hasNext()) {
60                  throw new NoSuchElementException();
61              }
62  
63              Object   temp = next;
64              next = NOOBJECT;
65              return temp;
66  
67          } else {
68              return next;
69          }
70      }
71  
72      /**
73       * We dont't support this.
74       */
75      public void remove() {
76          throw new UnsupportedOperationException  ();
77      }
78  }
79
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