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Java > Open Source Codes > org > jaxen > function > BooleanFunction


1 /*
2  * $Header: /home/projects/jaxen/scm/jaxen/src/java/main/org/jaxen/function/BooleanFunction.java,v 1.15 2005/06/26 16:07:22 elharo Exp $
3  * $Revision: 1.15 $
4  * $Date: 2005/06/26 16:07:22 $
5  *
6  * ====================================================================
7  *
8  * Copyright (C) 2000-2002 bob mcwhirter & James Strachan.
9  * All rights reserved.
10  *
11  * Redistribution and use in source and binary forms, with or without
12  * modification, are permitted provided that the following conditions
13  * are met:
14  *
15  * 1. Redistributions of source code must retain the above copyright
16  * notice, this list of conditions, and the following disclaimer.
17  *
18  * 2. Redistributions in binary form must reproduce the above copyright
19  * notice, this list of conditions, and the disclaimer that follows
20  * these conditions in the documentation and/or other materials
21  * provided with the distribution.
22  *
23  * 3. The name "Jaxen" must not be used to endorse or promote products
24  * derived from this software without prior written permission. For
25  * written permission, please contact license@jaxen.org.
26  *
27  * 4. Products derived from this software may not be called "Jaxen", nor
28  * may "Jaxen" appear in their name, without prior written permission
29  * from the Jaxen Project Management (pm@jaxen.org).
30  *
31  * In addition, we request (but do not require) that you include in the
32  * end-user documentation provided with the redistribution and/or in the
33  * software itself an acknowledgement equivalent to the following:
34  * "This product includes software developed by the
35  * Jaxen Project (http://www.jaxen.org/)."
36  * Alternatively, the acknowledgment may be graphical using the logos
37  * available at http://www.jaxen.org/
38  *
39  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
40  * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
41  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
42  * DISCLAIMED. IN NO EVENT SHALL THE Jaxen AUTHORS OR THE PROJECT
43  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
44  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
45  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
46  * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
47  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
48  * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
49  * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
50  * SUCH DAMAGE.
51  *
52  * ====================================================================
53  * This software consists of voluntary contributions made by many
54  * individuals on behalf of the Jaxen Project and was originally
55  * created by bob mcwhirter <bob@werken.com> and
56  * James Strachan <jstrachan@apache.org>. For more information on the
57  * Jaxen Project, please see <http://www.jaxen.org/>.
58  *
59  * $Id: BooleanFunction.java,v 1.15 2005/06/26 16:07:22 elharo Exp $
60  */
61
62
63 package org.jaxen.function;
64
65 import java.util.List JavaDoc;
66
67 import org.jaxen.Context;
68 import org.jaxen.Function;
69 import org.jaxen.FunctionCallException;
70 import org.jaxen.Navigator;
71
72 /**
73  * <p>
74  * <b>4.3</b> <code><i>boolean</i> boolean(<i>object</i>)</code>
75  * </p>
76  *
77  * <blockquote
78  * SRC="http://www.w3.org/TR/xpath#section-Boolean-Functions">
79  * <p>
80  * The <b><a HREF="http://www.w3.org/TR/xpath#function-boolean" target="_top">boolean</a></b>
81  * function converts its argument to a boolean as follows:
82  * </p>
83  *
84  * <ul>
85  *
86  * <li>
87  * <p>
88  * a number is true if and only if it is neither positive or negative
89  * zero nor NaN
90  * </p>
91  * </li>
92  *
93  * <li>
94  * <p>
95  * a node-set is true if and only if it is non-empty
96  * </p>
97  * </li>
98  *
99  * <li>
100  * <p>
101  * a string is true if and only if its length is non-zero
102  * </p>
103  * </li>
104  *
105  * <li>
106  *
107  * <p>
108  * an object of a type other than the four basic types is converted to a
109  * boolean in a way that is dependent on that type
110  * </p></li></ul>
111  * </blockquote>
112  *
113  * @author bob mcwhirter (bob @ werken.com)
114  * @see <a HREF="http://www.w3.org/TR/xpath#function-boolean">Section 4.3 of the XPath Specification</a>
115  */
116 public class BooleanFunction implements Function
117 {
118
119
120     /**
121      * Create a new <code>BooleanFunction</code> object.
122      */
123     public BooleanFunction() {}
124     
125     /** Convert the argument to a <code>Boolean</code>
126      *
127      * @param context the context at the point in the
128      * expression when the function is called
129      * @param args a list with exactly one item which will be converted to a
130      * <code>Boolean</code>
131      *
132      * @return the result of evaluating the function;
133      * <code>Boolean.TRUE</code> or <code>Boolean.FALSE</code>
134      *
135      * @throws FunctionCallException if <code>args</code> has more or less than one item
136      */
137     public Object JavaDoc call(Context context,
138                        List JavaDoc args) throws FunctionCallException
139     {
140         if ( args.size() == 1 )
141         {
142             return evaluate( args.get(0), context.getNavigator() );
143         }
144
145         throw new FunctionCallException("boolean() requires one argument");
146     }
147
148     /**
149      * <p>Convert the argument <code>obj</code> to a <code>Boolean</code>
150      * according to the following rules:</p>
151      *
152      * <ul>
153      * <li>Lists are false if they're empty; true if they're not.</li>
154      * <li>Booleans are false if they're false; true if they're true.</li>
155      * <li>Strings are false if they're empty; true if they're not.</li>
156      * <li>Numbers are false if they're 0 or NaN; true if they're not.</li>
157      * <li>All other objects are true.</li>
158      * </ul>
159      *
160      * @param obj the object to convert to a boolean
161      * @param nav ignored
162      *
163      * @return <code>Boolean.TRUE</code> or <code>Boolean.FALSE</code>
164      */
165     public static Boolean JavaDoc evaluate(Object JavaDoc obj, Navigator nav)
166     {
167         if ( obj instanceof List JavaDoc )
168         {
169             List JavaDoc list = (List JavaDoc) obj;
170             
171             // if it's an empty list, then we have a null node-set -> false
172 if (list.size() == 0)
173             {
174                 return Boolean.FALSE;
175             }
176      
177             // otherwise, unwrap the list and check the primitive
178 obj = list.get(0);
179         }
180         
181         // now check for primitive types
182 // otherwise a non-empty node-set is true
183
184         // if it's a Boolean, let it decide
185 if ( obj instanceof Boolean JavaDoc )
186         {
187             return (Boolean JavaDoc) obj;
188         }
189         // if it's a Number, != 0 -> true
190 else if ( obj instanceof Number JavaDoc )
191         {
192             double d = ((Number JavaDoc) obj).doubleValue();
193             if ( d == 0 || Double.isNaN(d) )
194             {
195                 return Boolean.FALSE;
196             }
197             return Boolean.TRUE;
198         }
199         // if it's a String, "" -> false
200 else if ( obj instanceof String JavaDoc )
201         {
202             return ( ((String JavaDoc)obj).length() > 0
203                      ? Boolean.TRUE
204                      : Boolean.FALSE );
205         }
206         else
207         {
208             // assume it's a node so that this node-set is non-empty
209 // and so it's true
210 return ( obj != null ) ? Boolean.TRUE : Boolean.FALSE;
211         }
212
213     }
214 }
215
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