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Java > Open Source Codes > net > sf > jga > util > GenericComparator


1 // ============================================================================
2 // $Id: GenericComparator.java,v 1.5 2005/08/02 23:45:22 davidahall Exp $
3 // Copyright (c) 2003-2005 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 package net.sf.jga.util;
33
34 import net.sf.jga.fn.UnaryFunctor;
35 import java.io.Serializable JavaDoc;
36 import java.util.Comparator JavaDoc;
37
38 /**
39  * Comparator that applies a functor to each argument, then compares the
40  * results. The functor must return Comparable values.
41  * <p>
42  * Copyright &copy; 2003-2005 David A. Hall
43  *
44  * @author <a HREF="mailto:davidahall@users.sf.net">David A. Hall</a>
45  */
46
47 public class GenericComparator<T,R extends Comparable JavaDoc<? super R>>
48     implements Comparator JavaDoc<T>, Serializable JavaDoc
49 {
50
51     static final long serialVersionUID = -2163248795946764874L;
52     
53     // The functor applied to both arguments in order to yield the value to be compared
54 private UnaryFunctor<T,R> _fn;
55
56     /**
57      * Builds a comparator that uses the given functor to derive the values that are to
58      * be compared.
59      */
60     public GenericComparator(UnaryFunctor<T,R> fn) {
61         if (fn == null)
62             throw new IllegalArgumentException JavaDoc("Functor is required");
63
64         _fn = fn;
65     }
66
67     /**
68      * Applies the functor to each of the two arguments, and compares the results.
69      */
70     public int compare(T x, T y) {
71         return _fn.fn(x).compareTo(_fn.fn(y));
72     }
73 }
74
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