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Java > Open Source Codes > net > sf > jga > fn > property > Cast


1 // ============================================================================
2 // $Id: Cast.java,v 1.6 2006/04/26 03:28:42 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.property;
34
35 import java.text.MessageFormat JavaDoc;
36 import net.sf.jga.fn.UnaryFunctor;
37
38 /**
39  * UnaryFunctor that returns its argument, cast to the given type. Executing
40  * the functor will throw ClassCastExceptions if the argument cannot be cast
41  * to the given type.
42  * <p>
43  * Copyright &copy; 2004-2005 David A. Hall
44  *
45  * @author <a HREF="mailto:davidahall@users.sourceforge.net">David A. Hall</a>
46  **/
47
48 public class Cast<T,R> extends UnaryFunctor<T,R> {
49
50     static final long serialVersionUID = 2712605844695159349L;
51
52     private Class JavaDoc<R> _class;
53
54     /**
55      * Builds a Cast fuctor that returns values cast to the given type.
56      * @throws IllegalArgumentException if the method name is null or empty, or
57      * if the argument type array is null.
58      */
59     public Cast(Class JavaDoc<R> cl) {
60         if (cl == null)
61             throw new IllegalArgumentException JavaDoc("A class must be given");
62         
63         _class = cl;
64     }
65
66
67     public Class JavaDoc<R> getCastClass() { return _class; }
68     
69     // UnaryPredicate interface
70
71     public R fn(T arg) {
72         // In Java 1.5, we could write this as
73 //
74 // return _class.cast(arg);
75 //
76 // but that isn't backwards compatable with 1.4, so
77 // we'll do it another way.
78
79         if (_class.isInstance(arg))
80             return (R) arg;
81
82         String JavaDoc msg = "Cannot cast [{0}] to class {1}";
83         Object JavaDoc[] args = new Object JavaDoc[]{arg, _class.getName()};
84         ClassCastException JavaDoc x = new ClassCastException JavaDoc(MessageFormat.format(msg, args));
85         throw x;
86     }
87
88     /**
89      * Calls the Visitor's <code>visit(InstanceOf)</code> method, if it
90      * implements the nested Visitor interface.
91      */
92     public void accept(net.sf.jga.fn.Visitor v) {
93         if (v instanceof Cast.Visitor)
94             ((Cast.Visitor)v).visit(this);
95         else
96             v.visit(this);
97     }
98     
99     // Object overrides
100
101     public String JavaDoc toString() {
102         return "Cast["+_class.getName()+"]";
103     }
104     
105    // AcyclicVisitor
106
107     /**
108      * Interface for classes that may interpret a <b>Cast</b>
109      * function.
110      */
111     public interface Visitor extends net.sf.jga.fn.Visitor {
112         public void visit(Cast host);
113     }
114 }
115
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