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1   /*
2    * $Header: /home/projects/jaxen/scm/jaxen/src/java/main/org/jaxen/function/SumFunction.java,v 1.11 2006/02/05 21:47:41 elharo Exp $
3    * $Revision: 1.11 $
4    * $Date: 2006/02/05 21:47:41 $
5    *
6    * ====================================================================
7    *
8    * Copyright 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 are
13   * met:
14   * 
15   *   * Redistributions of source code must retain the above copyright
16   *     notice, this list of conditions and the following disclaimer.
17   * 
18   *   * Redistributions in binary form must reproduce the above copyright
19   *     notice, this list of conditions and the following disclaimer in the
20   *     documentation and/or other materials provided with the distribution.
21   * 
22   *   * Neither the name of the Jaxen Project nor the names of its
23   *     contributors may be used to endorse or promote products derived 
24   *     from this software without specific prior written permission.
25   * 
26   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
27   * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
28   * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
29   * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
30   * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
31   * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
32   * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
33   * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
34   * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
35   * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
36   * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
37   *
38   * ====================================================================
39   * This software consists of voluntary contributions made by many 
40   * individuals on behalf of the Jaxen Project and was originally 
41   * created by bob mcwhirter <bob@werken.com> and 
42   * James Strachan <jstrachan@apache.org>.  For more information on the 
43   * Jaxen Project, please see <http://www.jaxen.org/>.
44   * 
45   * $Id: SumFunction.java,v 1.11 2006/02/05 21:47:41 elharo Exp $
46   */
47  
48  
49  package org.jaxen.function;
50  
51  import java.util.Iterator;
52  import java.util.List;
53  
54  import org.jaxen.Context;
55  import org.jaxen.Function;
56  import org.jaxen.FunctionCallException;
57  import org.jaxen.Navigator;
58  
59  /***
60   * <p><b>4.4</b> <code><i>number</i> sum(<i>node-set</i>)</code> </p>
61   * 
62   * <blockquote src="http://www.w3.org/TR/xpath#function-sum">
63   * The sum function returns the sum, for each node in the argument node-set, 
64   * of the result of converting the string-values of the node to a number.
65   * </blockquote>
66   * 
67   * @author bob mcwhirter (bob @ werken.com)
68   * @see <a href="http://www.w3.org/TR/xpath#function-sum" target="_top">Section 4.4 of the XPath Specification</a>
69   */
70  public class SumFunction implements Function
71  {
72  
73      /***
74       * Create a new <code>SumFunction</code> object.
75       */
76      public SumFunction() {}
77      
78      /*** Returns the sum of its arguments.
79       *
80       * @param context the context at the point in the
81       *         expression when the function is called
82       * @param args a list that contains exactly one item, also a <code>List</code>
83       * 
84       * @return a <code>Double</code> containing the sum of the items in <code>args.get(0)</code>
85       * 
86       * @throws FunctionCallException if <code>args</code> has more or less than one item;
87       *     or if the first argument is not a <code>List</code>
88       */
89      public Object call(Context context,
90                         List args) throws FunctionCallException
91      {
92  
93          if (args.size() == 1)
94          {
95              return evaluate( args.get(0),
96                               context.getNavigator() );
97          }
98  
99          throw new FunctionCallException( "sum() requires one argument." );
100     }
101 
102     /*** 
103      * Returns the sum of the items in a list.
104      * If necessary, each item in the list is first converted to a <code>Double</code>
105      * as if by the XPath <code>number()</code> function.
106      * 
107      * @param obj a <code>List</code> of numbers to be summed
108      * @param nav ignored
109      * 
110      * @return the sum of the list
111      * 
112      * @throws FunctionCallException if <code>obj</code> is not a <code>List</code>
113      */
114     public static Double evaluate(Object obj,
115                                   Navigator nav) throws FunctionCallException
116     {
117         double sum  = 0;
118 
119         if (obj instanceof List)
120         {
121             Iterator nodeIter = ((List)obj).iterator();
122             while ( nodeIter.hasNext() )
123             {
124                 double term = NumberFunction.evaluate( nodeIter.next(),
125                                                 nav ).doubleValue();
126                 sum += term;
127             }
128         }
129         else
130         {
131             throw new FunctionCallException("The argument to the sum function must be a node-set");
132         }
133 
134         return new Double(sum);
135     }
136     
137 }