BoundedIterator


1   package uk.co.jezuk.mango.iterators;
2   
3   /**
4    * A <code>BoundedIterator</code> enumerates of a subset of a collection, in the
5    * range [<code>start</code>, <code>end</code>).  A normal <code>java.util.Iterator</code> 
6    * traverses [0, collection.size()), so BoundedIterator allows you
7    * to pick out a sub-set without using <code>list.subList()</code> 
8    * or equivalent.
9    * 
10   * @author Jez Higgins, jez@jezuk.co.uk
11   * @version $Id: BoundedIterator.java 49 2002-06-11 14:43:09Z jez $
12   */
13  public class BoundedIterator implements java.util.Iterator  
14  {
15    /**
16     * This form of <code>BoundedIterator</code> limits the range traversed by the 
17     * underlying <code>iterator</code>. <p>
18     * If <code>iterator.hasNext()</code> fails before <code>end</code> is
19     * reached, the traversal will stop prematurely.<p>
20     * @throws java.lang.IndexOutOfBoundsException if start<0, end<0 or start>end
21     */
22    public BoundedIterator(java.util.Iterator   iterator, int start, int end)
23    {
24      iter_ = new iteratorWrapper(iterator, start, end);
25    } // BoundIterator
26    
27    /**
28     * The form of <code>BoundedIterator</code> uses indexed access directly into
29     * the list.<p>
30     * If <code>end</code> > list.end() the travesal will stop with
31     * list.end() is reached.<p>
32     * For <code>ArrayLists</code> and <code>Vectors</code> it 
33     * should be slightly quicker.  For <code>LinkedLists</code> it
34     * will be slower.
35     * @throws java.lang.IndexOutOfBoundsException if start<0, end<0 or start>end
36     */
37    public BoundedIterator(java.util.List   list, int start, int end)
38    {
39      iter_ = new listIterator(list, start, end);
40    } // BoundedIterator
41  
42    public boolean hasNext()
43    {
44      return iter_.hasNext();
45    } // hasNext
46  
47    public Object   next()
48    {
49      return iter_.next();
50    } // next
51  
52    public void remove()
53    {
54      iter_.remove();
55    } // remove
56  
57    private java.util.Iterator   iter_;
58  
59    ///////////////////////////////////////////////////
60    static private void checkConstraints(int start, int end)
61    {
62      if(start < 0)
63        throw new IndexOutOfBoundsException  ("start < 0");
64      if(end < 0)
65        throw new IndexOutOfBoundsException  ("end < 0");
66      if(start > end)
67        throw new IndexOutOfBoundsException  ("start > end");
68    } // checkConstraints
69  
70    static private class iteratorWrapper implements java.util.Iterator  
71    {
72      iteratorWrapper(java.util.Iterator   iterator, int start, int end)
73      {
74        BoundedIterator.checkConstraints(start, end);
75  
76        iter_ = iterator;
77        for(index_ = 0; iter_.hasNext() && index_ < start; ++index_, iter_.next())
78      ;
79  
80        end_ = iter_.hasNext() ? end : index_;
81      } // iteratorWrapper
82  
83      public boolean hasNext()
84      {
85        end_ = iter_.hasNext() ? end_ : index_;
86        return (index_ < end_);
87      } // hasNext()
88  
89      public Object   next()
90      {
91        ++index_;
92        return iter_.next();
93      } // next
94  
95      public void remove()
96      {
97        iter_.remove();
98      } // remove
99  
100     private java.util.Iterator   iter_;
101     private int index_;
102     private int end_;
103   } // iteratorWrapper
104 
105   static private class listIterator implements java.util.Iterator  
106   {
107     listIterator(java.util.List   list, int start, int end)
108     {
109       BoundedIterator.checkConstraints(start, end);
110 
111       list_ = list;
112       index_ = start;
113       end_ = end;
114 
115       if(end_ > list_.size())
116     end_ = list.size();
117     } // listIterator
118 
119     public boolean hasNext()
120     {
121       return (index_ < end_);
122     } // hasNext
123 
124     public Object   next()
125     {
126       return list_.get(index_++);
127     } // next
128 
129     public void remove()
130     {
131       list_.remove(index_ - 1);
132     } // remove
133 
134     private java.util.List   list_;
135     private int index_;
136     private int end_;
137   } // listIterator
138 } // BoundedIterator
139
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