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Java > Open Source Codes > net > sf > jga > fn > algorithm > ElementOf


1 // ============================================================================
2 // $Id: ElementOf.java,v 1.11 2006/01/08 00:52:25 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.fn.algorithm;
33
34 import java.util.Collection JavaDoc;
35 import net.sf.jga.fn.BinaryFunctor;
36 import net.sf.jga.fn.UnaryFunctor;
37 import net.sf.jga.fn.BinaryPredicate;
38 import net.sf.jga.util.FindIterator;
39
40 /**
41  * BinaryPredicate that returns true if a given value is an element of a
42  * given collection.
43  * <p>
44  * Copyright &copy; 2003-2005 David A. Hall
45  *
46  * @author <a HREF="mailto:davidahall@users.sf.net">David A. Hall</a>
47  */
48
49 public class ElementOf<T> extends BinaryPredicate<T, Collection JavaDoc<? extends T>> {
50     
51     static final long serialVersionUID = 4639100512962835854L;
52     
53     // The functor used to compare the element to the items in the collection
54 private BinaryFunctor<T,T,Boolean JavaDoc> _eq;
55
56     /**
57      * Builds an ElementOf predicate that will use the collection's built in
58      * contains() method. This form is potentially more efficient than the
59      * other constructed form, if the collection passed at evaluation
60      * implements contains() using an algorithm more efficient than a linear
61      * search.
62      */
63     public ElementOf() {}
64     
65     /**
66      * Builds an ElementOf predicate that will use the given functor to
67      * determine collection membership. The collection will be searched
68      * sequentially for the first element for which the functor returns true.
69      */
70     public ElementOf(BinaryFunctor<T,T,Boolean JavaDoc> eq) {
71         _eq = eq;
72     }
73
74     /**
75      * Returns the (possibly null) functor used to compare a value to the
76      * contents of a collection.
77      */
78     public BinaryFunctor<T,T,Boolean JavaDoc> getComparisonFn() {
79         return _eq;
80     }
81
82     /**
83      * Return true if the given value is an element of the collection
84      */
85     public Boolean JavaDoc fn(T value, Collection JavaDoc<? extends T> collection) {
86         if (_eq == null)
87             return collection.contains(value);
88         else {
89             FindIterator<T> finder =
90                 new FindIterator<T>(collection.iterator());
91             UnaryFunctor<T,Boolean JavaDoc> uf = _eq.bind2nd(value);
92             return finder.findNext(uf);
93         }
94     }
95     
96     /**
97      * Calls the Visitor's <code>visit(ElementOf)</code> method, if it
98      * implements the nested Visitor interface.
99      */
100     public void accept(net.sf.jga.fn.Visitor v) {
101         if (v instanceof ElementOf.Visitor)
102             ((ElementOf.Visitor)v).visit(this);
103         else
104             v.visit(this);
105     }
106
107     // Object overrides
108
109     public String JavaDoc toString() {
110         return "ElementOf";
111     }
112     
113     // AcyclicVisitor
114
115     /**
116      * Interface for classes that may interpret an <b>ElementOf</b> functor.
117      */
118     public interface Visitor extends net.sf.jga.fn.Visitor {
119         public void visit(ElementOf host);
120     }
121 }
122
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