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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;
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 call(Context context,
138                        List 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 evaluate(Object obj, Navigator nav)
166     {
167         if ( obj instanceof List )
168         {
169             List list = (List) 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 )
186         {
187             return (Boolean) obj;
188         }
189         // if it's a Number, != 0 -> true
190         else if ( obj instanceof Number )
191         {
192             double d = ((Number) 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 )
201         {
202             return ( ((String)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 }