NumberFunction


1   /*
2    * $Header: /home/projects/jaxen/scm/jaxen/src/java/main/org/jaxen/function/NumberFunction.java,v 1.16 2005/06/26 16:07:22 elharo Exp $
3    * $Revision: 1.16 $
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 
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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 
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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
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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
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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: NumberFunction.java,v 1.16 2005/06/26 16:07:22 elharo Exp $
60   */
61  
62  package org.jaxen.function;
63  
64  import java.util.Iterator  ;
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>4.4</b> <code><i>number</i> number(<i>object</i>)</code>
75   * 
76   * 
77   * <blockquote SRC="http://www.w3.org/TR/xpath#function-number">
78   * <p>
79   * The <b>number</b> function converts
80   * its argument to a number as follows:
81   * </p>
82   * 
83   * <ul>
84   * 
85   * <li>
86   * <p>
87   * a string that consists of optional whitespace followed by an optional
88   * minus sign followed by a <a HREF="#NT-Number">Number</a> followed by
89   * whitespace is converted to the IEEE 754 number that is nearest
90   * (according to the IEEE 754 round-to-nearest rule) to the mathematical
91   * value represented by the string; any other string is converted to NaN
92   * </p>
93   * </li>
94   * 
95   * <li>
96   * <p>
97   * boolean true is converted to 1; boolean false is converted to 0
98   * </p>
99   * </li>
100  * 
101  * <li>
102  * 
103  * <p>
104  * a node-set is first converted to a string as if by a call to the <b><a
105  * HREF="http://www.w3.org/TR/xpath#function-string" target="_top">string</a></b> function and then converted
106  * in the same way as a string argument
107  * </p>
108  * 
109  * </li>
110  * 
111  * <li>
112  * <p>
113  * an object of a type other than the four basic types is converted to a
114  * number in a way that is dependent on that type
115  * </p>
116  * </li>
117  * 
118  * </ul>
119  * 
120  * <p>
121  * If the argument is omitted, it defaults to a node-set with the
122  * context node as its only member.
123  * </p>
124  * 
125  * <blockquote> <b>NOTE: </b>The <b>number</b>
126  * function should not be used for conversion of numeric data occurring
127  * in an element in an XML document unless the element is of a type that
128  * represents numeric data in a language-neutral format (which would
129  * typically be transformed into a language-specific format for
130  * presentation to a user). In addition, the <b>number</b> function cannot be used
131  * unless the language-neutral format used by the element is consistent
132  * with the XPath syntax for a <a HREF="http://www.w3.org/TR/xpath#NT-Number">Number</a>.</blockquote>
133  * 
134  * </blockquote>
135  * 
136  * @author bob mcwhirter (bob @ werken.com)
137  * 
138  * @see <a HREF="http://www.w3.org/TR/xpath#function-number"
139  *      target="_top">Section 4.4 of the XPath Specification</a>
140  */
141 public class NumberFunction implements Function
142 {
143 
144     private final static Double   NaN = new Double  ( Double.NaN );
145     
146     
147     /**
148      * Create a new <code>NumberFunction</code> object.
149      */
150     public NumberFunction() {}
151 
152     /** 
153      * Returns the number value of <code>args.get(0)</code>,
154      * or the number value of the context node if <code>args</code>
155      * is empty.
156      *
157      * @param context the context at the point in the
158      *         expression when the function is called
159      * @param args a list containing the single item to be converted to a 
160      *     <code>Double</code>
161      * 
162      * @return a <code>Double</code>
163      * 
164      * @throws FunctionCallException if <code>args</code> has more than one item
165      */
166     public Object   call(Context context, List   args) throws FunctionCallException
167     {
168         if (args.size() == 1)
169         {
170             return evaluate( args.get(0), context.getNavigator() );
171         }
172         else if (args.size() == 0)
173         {
174             return evaluate( context.getNodeSet(), context.getNavigator() );
175         }
176     
177         throw new FunctionCallException( "number() takes at most one argument." );
178     }
179 
180     /** 
181      * Returns the number value of <code>obj</code>.
182      *
183      * @param obj the object to be converted to a number
184      * @param nav the <code>Navigator</code> used to calculate the string-value
185      *     of node-sets
186      * 
187      * @return a <code>Double</code>
188      */
189     public static Double   evaluate(Object   obj, Navigator nav)
190     {
191         if( obj instanceof Double   )
192         {
193             return (Double  ) obj;
194         }
195         else if ( obj instanceof String   )
196         {
197             String   str = (String  ) obj;
198             try
199             {
200                 Double   doubleValue = new Double  ( str );        
201                 return doubleValue;
202             }
203             catch (NumberFormatException   e)
204             {
205                 return NaN;
206             }
207         }
208         else if ( obj instanceof List   || obj instanceof Iterator   )
209         {
210           return evaluate( StringFunction.evaluate( obj, nav ), nav );
211         }
212         else if ( nav.isElement( obj ) || nav.isAttribute( obj ) )
213         {
214             return evaluate( StringFunction.evaluate( obj, nav ), nav );
215         }
216         else if ( obj instanceof Boolean   )
217           {
218           if ( obj == Boolean.TRUE )
219           {
220               return new Double  ( 1 );
221           }
222           else
223           {
224               return new Double  ( 0 );
225           }
226         }    
227         return NaN;
228     }
229   
230   /**
231    * Determines whether the argument is not a number (NaN) as defined
232    * by IEEE 754.
233    * 
234    * @param val the double to test
235    * @return true if the value is NaN, false otherwise
236    */
237     public static boolean isNaN( double val )
238     {
239         return Double.isNaN(val);
240     }
241   
242   /**
243    * Determines whether the argument is not a number (NaN) as defined
244    * by IEEE 754.
245    * 
246    * @param val the <code>Double</code> to test
247    * @return true if the value is NaN, false otherwise
248    */
249     public static boolean isNaN( Double   val )
250     {
251         return val.equals( NaN );
252     }  
253   
254 }
255
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