JoinedIterator


1   //$Id: JoinedIterator.java,v 1.2 2004/06/28 23:58:08 epbernard Exp $
2   package org.hibernate.util;
3   
4   import java.util.Iterator  ;
5   import java.util.List  ;
6   
7   /**
8    * An JoinedIterator is an Iterator that wraps a number of Iterators.
9    *
10   * This class makes multiple iterators look like one to the caller.
11   * When any method from the Iterator interface is called, the JoinedIterator
12   * will delegate to a single underlying Iterator. The JoinedIterator will
13   * invoke the Iterators in sequence until all Iterators are exhausted.
14   *
15   */
16  public class JoinedIterator implements Iterator   {
17  
18      private static final Iterator  [] ITERATORS = {};
19  
20      // wrapped iterators
21      private Iterator  [] iterators;
22  
23      // index of current iterator in the wrapped iterators array
24      private int currentIteratorIndex;
25  
26      // the current iterator
27      private Iterator   currentIterator;
28  
29      // the last used iterator
30      private Iterator   lastUsedIterator;
31  
32      public JoinedIterator(List   iterators) {
33          this( (Iterator  []) iterators.toArray(ITERATORS) );
34      }
35  
36      public JoinedIterator(Iterator  [] iterators) {
37          if( iterators==null )
38              throw new NullPointerException  ("Unexpected NULL iterators argument");
39          this.iterators = iterators;
40      }
41  
42      public JoinedIterator(Iterator   first, Iterator   second) {
43          this( new Iterator  [] { first, second } );
44      }
45  
46      public boolean hasNext() {
47          updateCurrentIterator();
48          return currentIterator.hasNext();
49      }
50  
51      public Object   next() {
52          updateCurrentIterator();
53          return currentIterator.next();
54      }
55  
56      public void remove() {
57          updateCurrentIterator();
58          lastUsedIterator.remove();
59      }
60  
61  
62      // call this before any Iterator method to make sure that the current Iterator
63      // is not exhausted
64      protected void updateCurrentIterator() {
65  
66          if (currentIterator == null) {
67              if( iterators.length==0  ) {
68                  currentIterator = EmptyIterator.INSTANCE;
69              }
70              else {
71                  currentIterator = iterators[0];
72              }
73              // set last used iterator here, in case the user calls remove
74              // before calling hasNext() or next() (although they shouldn't)
75              lastUsedIterator = currentIterator;
76          }
77  
78          while (! currentIterator.hasNext() && currentIteratorIndex < iterators.length - 1) {
79              currentIteratorIndex++;
80              currentIterator = iterators[currentIteratorIndex];
81          }
82      }
83  
84  }
85
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