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Java > Open Source Codes > org > archive > util > iterator > TransformingIteratorWrapper


1 /* TransformingIteratorWrapper
2 *
3 * $Id: TransformingIteratorWrapper.java,v 1.3.16.1 2007/01/13 01:31:40 stack-sf Exp $
4 *
5 * Created on Mar 25, 2005
6 *
7 * Copyright (C) 2005 Internet Archive.
8 *
9 * This file is part of the Heritrix web crawler (crawler.archive.org).
10 *
11 * Heritrix is free software; you can redistribute it and/or modify
12 * it under the terms of the GNU Lesser Public License as published by
13 * the Free Software Foundation; either version 2.1 of the License, or
14 * any later version.
15 *
16 * Heritrix is distributed in the hope that it will be useful,
17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19 * GNU Lesser Public License for more details.
20 *
21 * You should have received a copy of the GNU Lesser Public License
22 * along with Heritrix; if not, write to the Free Software
23 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
24 */
25 package org.archive.util.iterator;
26
27 import java.util.Iterator JavaDoc;
28
29 /**
30  * Superclass for Iterators which transform and/or filter results
31  * from a wrapped Iterator. Because transform() has the option of
32  * discarding an item from the inner Iterator (by returning null),
33  * this is a kind of LookaheadIterator.
34  *
35  * @author gojomo
36  */
37 public abstract class TransformingIteratorWrapper<Original,Transformed>
38 extends LookaheadIterator<Transformed> {
39     protected Iterator JavaDoc<Original> inner;
40     
41     
42     /* (non-Javadoc)
43      * @see org.archive.util.iterator.LookaheadIterator#lookahead()
44      */
45     protected boolean lookahead() {
46         assert next == null : "looking ahead when next is already loaded";
47         while(inner.hasNext()) {
48             next = transform(inner.next());
49             if(next!=null) {
50                 return true;
51             }
52         }
53         noteExhausted();
54         return false;
55     }
56
57     /**
58      * Any cleanup to occur when hasNext() is about to return false
59      */
60     protected void noteExhausted() {
61         // by default, do nothing
62
63     }
64
65     /**
66      * @param object Object to transform.
67      * @return Transfomed object.
68      */
69     protected abstract Transformed transform(Original object);
70
71 }
72
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