KickJava   Java API By Example, From Geeks To Geeks.

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


1 // ============================================================================
2
// $Id: EqualTo.java,v 1.17 2006/08/07 03:59:48 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
37 /**
38  * Binary Predicate that returns TRUE for object arguments <b>x</b> and
39  * <b>y</b> when x == y using the built-in equals() method or an optional
40  * Comparator given at construction. By default, this functor will not throw
41  * NullPointerException: it will return true if both runtime arguments are null
42  * but false if only one is null. If an optional comparator is used, then its
43  * implementation will determine if a NullPointerException is thrown when passed
44  * a null argument.
45  * <p>
46  * To serialize an Equal functor, the comparator passed at construction(if any)
47  * must be Serializable.
48  * <p>
49  * Copyright &copy; 2002-2005 David A. Hall
50  *
51  * @author <a HREF="mailto:davidahall@users.sourceforge.net">David A. Hall</a>
52  **/

53
54 public class EqualTo<T> extends Equality<T> {
55
56     static final long serialVersionUID = -8880072682296106379L;
57
58     // An optional comparator used to compare values
59
Comparator JavaDoc<? super T> _comp;
60
61     /**
62      * Builds an EqualTo that uses the built-in equals method.
63      */

64     public EqualTo() {}
65     
66     /**
67      * Builds an EqualTo that uses the given comparator.
68      */

69     public EqualTo(Comparator JavaDoc<? super T> comp) {
70         _comp = comp;
71     }
72     
73     /**
74      * Returns the comparator in use by this functor, if any.
75      * @return the comparator in use by this functor, if any.
76      */

77     public Comparator JavaDoc<? super T> getComparator() { return _comp; }
78     
79     // BinaryFunctor interface
80

81     /**
82      * Given arguments <b>x</b> and <b>y</b>, returns x.equals(y). Will not
83      * throw NullPointerException if either x or y are null: will return true
84      * if both x and y are null and false if either x or y are null.
85      *
86      * @return x.equals(y)
87      */

88     public Boolean JavaDoc fn(T x, T y) {
89         if (_comp == null)
90             return (x == null) ? y == null : x.equals(y);
91         else
92             return _comp.compare(x, y) == 0;
93     }
94
95     /**
96      * Calls the Visitor's <code>visit(EqualTo)</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 EqualTo.Visitor)
101             ((EqualTo.Visitor)v).visit(this);
102         else
103             v.visit(this);
104     }
105
106     // Object overrides
107

108     public String JavaDoc toString() {
109         return "EqualTo";
110     }
111     
112     // Acyclic Visitor
113

114     /**
115      * Interface for classes that may interpret an <b>EqualTo</b> predicate.
116      */

117     public interface Visitor extends net.sf.jga.fn.Visitor {
118         public void visit(EqualTo host);
119     }
120 }
121
Popular Tags