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Java > Open Source Codes > net > sf > jga > fn > Visitor


1 // ============================================================================
2 // $Id: Visitor.java,v 1.4 2006/01/08 00:52:25 davidahall Exp $
3 // Copyright (c) 2002-2005 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;
34
35 /**
36  * Defines an interface for classes that may interpret functors or predicates.
37  * <p>
38  * jga uses the <a HREF="http://www.objectmentor.com/resources/articles/acv.pdf">AcyclicVisitor</a>
39  * pattern to provide a structure for implementing Visitor. Within jga, each
40  * class that implements Visitable does so with the following boilerplate:<br>
41  * <pre>
42  * public class Foo implements Visitable
43  * public void accept(net.sf.jga.fn.Visitor v) {
44  * if (v instanceof Foo.Visitor)
45  * ((Foo.Visitor)v).visit(this);
46         else
47             v.visit(this);
48  * }
49  *
50  * public interface Visitor extends net.sf.jga.fn.Visitor {
51  * public void visit(Foo host);
52  * }
53  * </pre>
54  * Implementations of Visitor will declare suport for a given class by
55  * implementing that class' Visitor interface.<br>
56  * <pre>
57  * public class FooBarCounter implements Foo.Visitor, Bar.Visitor {
58  * private int count = 0;
59  * public int getCount() { return count; }
60  * public void visit(Visitable host) {}
61  * public void visit(Foo host) { ++count; }
62  * public void visit(Bar host) { ++count; }
63  * }
64  * </pre>
65  * <p>
66  * Copyright &copy; 2002-2005 David A. Hall
67  *
68  * @author <a HREF="mailto:davidahall@users.sourceforge.net">David A. Hall</a>
69  **/
70
71 public interface Visitor {
72     /**
73      * Call-back method, called by the Visitable object in response to a
74      * call to its <code>accept(Visitor)</code> method.
75      */
76     public void visit(Visitable visitable);
77 }
78
79     
80
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