01: // ============================================================================
02: // $Id: LookAheadFunctor.java,v 1.5 2006/08/10 03:33:51 davidahall Exp $
03: // Copyright (c) 2004-2005 David A. Hall
04: // ============================================================================
05: // The contents of this file are subject to the Common Development and
06: // Distribution License (CDDL), Version 1.0 (the License); you may not use this
07: // file except in compliance with the License. You should have received a copy
08: // of the the License along with this file: if not, a copy of the License is
09: // 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;
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 © 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> extends
52: UnaryFunctor<Iterator<? extends T>, LookAheadIterator<T>> {
53: /**
54: * Conditionally wraps the input iterator in a LookAheadIterator for return.
55: * Uses a Wrapper to determine if the input iterator is one that this
56: * object has already built and returned: if so, then there is no need
57: * to wrap it again.
58: */
59: protected LookAheadIterator<T> wrap(Iterator<? extends T> iterator,
60: int count) {
61: if (iterator instanceof Wrapper
62: && ((Wrapper) iterator).owner == this )
63: // @SuppressWarnings
64: // The preceding condition can only be true if the iterator argument was
65: // created by the constructor call three lines hence, and will always be
66: // true in that case.
67: return (LookAheadIterator<T>) iterator;
68:
69: return new Wrapper<T>(this , iterator, count);
70: }
71:
72: /**
73: * Wrapper class used to prevent excessive creation of wrapper interators.
74: * This class stores a reference to its caller (which is an instance of the
75: * enclosing class).
76: */
77: static private class Wrapper<T> extends LookAheadIterator<T> {
78: private LookAheadFunctor<T> owner;
79:
80: public Wrapper(LookAheadFunctor<T> owner,
81: Iterator<? extends T> iter, int count) {
82: super(iter, count);
83: this.owner = owner;
84: }
85: }
86: }
|