TransformingIterator


1   /*
2    * TransformingIterator.java
3    */
4   
5   package polyglot.util;
6   
7   import java.util.Iterator  ;
8   import java.util.Collection  ;
9   
10  /**
11   * TransformingIterator
12   *
13   * Overview:
14   *     This is a swiss-army-knife of iterators.  It concatenates, maps, and
15   *     filters.  
16   *
17   *     Does not support Remove.
18   **/
19  public final class TransformingIterator implements Iterator   {
20    public TransformingIterator(Iterator   iter, Transformation trans) {
21      this(new Iterator  []{iter}, trans);
22    }
23  
24    public TransformingIterator(Collection   iters, Transformation trans) {
25      index = 0;
26      backing_iterators = (Iterator  []) iters.toArray(new Iterator  [0]);
27      transformation = trans;
28      if (backing_iterators.length > 0)
29        current_iter = backing_iterators[0];
30      findNextItem();
31    }
32  
33    public TransformingIterator(Iterator  [] iters, Transformation trans) {
34      index = 0;
35      backing_iterators = (Iterator  []) iters.clone();
36      transformation = trans;
37      if (iters.length > 0) 
38        current_iter = iters[0];
39      findNextItem();
40    }
41  
42    public Object   next() {
43      Object   res = next_item;
44      if (res == null)
45        throw new java.util.NoSuchElementException  ();
46      findNextItem();
47      return res;
48    }
49  
50    public boolean hasNext() {
51      return next_item != null;
52    }
53    
54    public void remove() {
55      throw new UnsupportedOperationException  ("TransformingIterator.remove");
56    }
57  
58    // Advances the internal iterator.
59    private void findNextItem() {
60      while (current_iter != null) {
61      inner_loop:
62        while (current_iter.hasNext()) {      
63      Object   o = current_iter.next(); 
64      Object   res = transformation.transform(o);
65      if (res == Transformation.NOTHING)
66        continue inner_loop;
67      next_item = res;
68      return;
69        }
70        index++;
71        if (index < backing_iterators.length) {
72      current_iter = backing_iterators[index];
73        } else {
74      current_iter = null;
75        }
76      }
77      next_item = null;
78    }
79    
80    // AF:  if next_item==null, this iterator has no more elts to yield.
81    //      otherwise, this iterator will yield next_item, followed by
82    //      those elements e of backing_iterator[index] transformed by TRANS.
83    // RI: current_iter = backing_iterators[index], or null if no 
84    //     backing_iterator hasNext.
85    Object   next_item;
86    Iterator   current_iter;
87    int index;
88    Iterator  [] backing_iterators;
89    Transformation transformation;
90  }
91  
92  
93
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