ConcatenatedIterator


1   /*
2    * ConcatenatedIterator.java
3    */
4   
5   package polyglot.util;
6   
7   import java.util.Iterator  ;
8   
9   /**
10   * ConcatenatedIterator
11   *
12   * Overview:
13   *     This iterator wraps other iterators, and returns all their elements
14   *     in order.
15   *
16   *     Does not support Remove.
17   **/
18  public final class ConcatenatedIterator implements Iterator   {
19    /**
20     * Constructs a new ConcatenatedIterator which yields all of the
21     * elements of <iter1>, followed by all the elements of <iter2>.
22     **/
23    public ConcatenatedIterator(Iterator   iter1, Iterator   iter2) {
24      this(new Iterator  []{iter1, iter2});
25    }
26  
27    /**
28     * Constructs a new ConcatenatedIterator which yields every element, in
29     *  order, of every element of the array iters, in order.
30     **/
31    public ConcatenatedIterator(Iterator  [] iters) {
32      this.backing_iterators = (Iterator  []) iters.clone();
33      findNextItem();
34    }
35  
36    /**
37     * Constructs a new ConcatenatedIterator which yields every element, in
38     * order, of every element of the collection iters, in order.
39     **/
40    public ConcatenatedIterator(java.util.Collection   iters) {
41      this.backing_iterators = (Iterator  [])iters.toArray(new Iterator  [0]);
42      findNextItem();
43    }
44  
45    public Object   next() {
46      Object   res = next_item;
47      if (res == null)
48        throw new java.util.NoSuchElementException  ();
49      findNextItem();
50      return res;
51    }
52  
53    public boolean hasNext() {
54      return next_item != null;
55    }
56    
57    public void remove() {
58      throw new UnsupportedOperationException  ("ConcatenatedIterator.remove");
59    }
60  
61    // Advances the internal iterator.
62    private void findNextItem() {
63      while(index < backing_iterators.length) {
64        Iterator   it = backing_iterators[index];
65        if (it.hasNext()) {
66      next_item = it.next();
67      return;
68        } else {
69      index++;
70        }
71      }
72      next_item = null;
73    }
74    
75    // AF:  if next_item==null, this iterator has no more elts to yield.
76    //      otherwise, this iterator will yield next_item, followed by the 
77    //      remaining elements of backing_iterators[index], followed by the
78    //      elements of backing_iterators[index+1]...
79    Object   next_item;
80    Iterator  [] backing_iterators;
81    int index;
82  }
83  
84  
85
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