KickJava   Java API By Example, From Geeks To Geeks.

Java > Open Source Codes > net > sf > jga > fn > algorithm > LookAheadFunctor


1 // ============================================================================
2 // $Id: LookAheadFunctor.java,v 1.5 2006/08/10 03:33:51 davidahall Exp $
3 // Copyright (c) 2004-2005 David A. Hall
4 // ============================================================================
5 // The contents of this file are subject to the Common Development and
6 // Distribution License (CDDL), Version 1.0 (the License); you may not use this
7 // file except in compliance with the License. You should have received a copy
8 // of the the License along with this file: if not, a copy of the License is
9 // available from Sun Microsystems, Inc.
10 //
11 // http://www.sun.com/cddl/cddl.html
12 //
13 // From time to time, the license steward (initially Sun Microsystems, Inc.) may
14 // publish revised and/or new versions of the License. You may not use,
15 // distribute, or otherwise make this file available under subsequent versions
16 // of the License.
17 //
18 // Alternatively, the contents of this file may be used under the terms of the
19 // GNU Lesser General Public License Version 2.1 or later (the "LGPL"), in which
20 // case the provisions of the LGPL are applicable instead of those above. If you
21 // wish to allow use of your version of this file only under the terms of the
22 // LGPL, and not to allow others to use your version of this file under the
23 // terms of the CDDL, indicate your decision by deleting the provisions above
24 // and replace them with the notice and other provisions required by the LGPL.
25 // If you do not delete the provisions above, a recipient may use your version
26 // of this file under the terms of either the CDDL or the LGPL.
27 //
28 // This library is distributed in the hope that it will be useful,
29 // but WITHOUT ANY WARRANTY; without even the implied warranty of
30 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
31 // ============================================================================
32
33 package net.sf.jga.fn.algorithm;
34
35 import java.util.Iterator JavaDoc;
36 import net.sf.jga.fn.UnaryFunctor;
37 import net.sf.jga.util.LookAheadIterator;
38
39 /**
40  * Abstract base class for functors that take an input iterator and return a
41  * LookAheadIterator. This class provides the ability to prevent excessive
42  * iterator wrapping by tracking the identity of the functor that has produced
43  * the wrapped iterator, and not re-wrapping an iterator if it was produced by
44  * the same object that is currently requesting a wrapped iterator.
45  * <p>
46  * Copyright &copy; 2004-2005 David A. Hall
47  *
48  * @author <a HREF="mailto:davidahall@users.sf.net">David A. Hall</a>
49  */
50
51 abstract class LookAheadFunctor<T>
52     extends UnaryFunctor<Iterator JavaDoc<? extends T>,LookAheadIterator<T>>
53 {
54     /**
55      * Conditionally wraps the input iterator in a LookAheadIterator for return.
56      * Uses a Wrapper to determine if the input iterator is one that this
57      * object has already built and returned: if so, then there is no need
58      * to wrap it again.
59      */
60     protected LookAheadIterator<T> wrap(Iterator JavaDoc<? extends T> iterator, int count) {
61         if (iterator instanceof Wrapper && ((Wrapper)iterator).owner == this)
62             // @SuppressWarnings
63 // The preceding condition can only be true if the iterator argument was
64 // created by the constructor call three lines hence, and will always be
65 // true in that case.
66 return (LookAheadIterator<T>) iterator;
67   
68         return new Wrapper<T>(this, iterator, count);
69     }
70
71     /**
72      * Wrapper class used to prevent excessive creation of wrapper interators.
73      * This class stores a reference to its caller (which is an instance of the
74      * enclosing class).
75      */
76     static private class Wrapper<T> extends LookAheadIterator<T> {
77         private LookAheadFunctor<T> owner;
78         public Wrapper(LookAheadFunctor<T> owner, Iterator JavaDoc<? extends T> iter, int count) {
79             super(iter, count); this.owner = owner;
80         }
81     }
82 }
83
Popular Tags