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Java > Open Source Codes > net > sf > jga > fn > comparison > LessEqual


1 // ============================================================================
2 // $Id: LessEqual.java,v 1.16 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.comparison;
34
35 import java.util.Comparator JavaDoc;
36 import net.sf.jga.fn.BinaryPredicate;
37 import net.sf.jga.util.ComparableComparator;
38
39 /**
40  * Binary Predicate that returns TRUE for arguments <b>x</b> and <b>y</b> when
41  * x &lt;= y. The comparison is performed using a comparator supplied at
42  * construction time, although a default comparator will be used if the nested
43  * Comparable class' default constructor is used.
44  * The behaviour of this class in the presence of null arguments is left to the
45  * implementation of the specific Comparator, however it is generally safe to
46  * assume that using null arguments will cause a NullPointerException to be
47  * thrown.
48  * <p>
49  * To serialize a LessEqual predicate , the comparator passed at construction
50  * must be Serializable.
51  * <p>
52  * Copyright &copy; 2002-2005 David A. Hall
53  *
54  * @author <a HREF="mailto:davidahall@users.sourceforge.net">David A. Hall</a>
55  **/
56
57 public class LessEqual<T> extends BinaryPredicate<T,T> {
58
59     static final long serialVersionUID = -4317901638908328747L;
60
61     // The Comparator used to compare elements.
62 private Comparator JavaDoc/*@*/<? super T>/*@*/ _comp;
63     
64     /**
65      * Builds a LessEqual predicate using the given Comparator.
66      * @throws IllegalArgumentException if the argument is null
67      */
68     public LessEqual(Comparator JavaDoc/*@*/<? super T>/*@*/ comp) {
69         if (comp == null) {
70             throw new IllegalArgumentException JavaDoc("Comparator may not be null");
71         }
72         
73         _comp = comp;
74     }
75
76     /**
77      * Returns the comparator in use by this functor
78      * @return the comparator in use by this functor
79      */
80     public Comparator JavaDoc<? super T> getComparator() { return _comp; }
81     
82     // BinaryPredicate interface
83
84     /**
85      * Given Comparable arguments <b>x</b> and <b>y</b>, returns x &lt;= y.
86      *
87      * @throws NullPointerException if either argument is null
88      * @return x &lt;= y
89      */
90     
91     public Boolean JavaDoc fn(T x, T y) {
92         return Boolean.valueOf(_comp.compare(x, y) <= 0);
93     }
94
95     /**
96      * Calls the Visitor's <code>visit(LessEqual)</code> method, if it
97      * implements the nested Visitor interface.
98      */
99     public void accept(net.sf.jga.fn.Visitor v) {
100         if (v instanceof LessEqual.Visitor)
101             ((LessEqual.Visitor)v).visit(this);
102         else
103             v.visit(this);
104     }
105
106     // Object overrides
107
108     public String JavaDoc toString() {
109         return "LessEqual";
110     }
111     
112     // Acyclic Visitor
113
114     /**
115      * Interface for classes that may interpret a <b>LessEqual</b> predicate.
116      */
117     public interface Visitor extends net.sf.jga.fn.Visitor {
118         public void visit(LessEqual host);
119     }
120
121     /**
122      * LessEqual predicate for use with Comparable arguments. This class exists
123      * as an implementation detail that works around a limit in the javac
124      * inferencer -- in all substantive ways, this is simply a LessEqual functor.
125      */
126
127     static public class Comparable<T extends java.lang.Comparable JavaDoc/*@*/<? super T>/*@*/>
128             extends LessEqual<T>
129     {
130         static final long serialVersionUID = 2318301997226073587L;
131         public Comparable() { super(new ComparableComparator<T>()); }
132     }
133 }
134
135
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