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A lib to access XML via XPath
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/*
 * $Header: /cvs/jaxen/jaxen/src/java/main/org/jaxen/function/SumFunction.java,v 1.11 2006/02/05 21:47:41 elharo Exp $
 * $Revision: 1.11 $
 * $Date: 2006/02/05 21:47:41 $
 *
 * ====================================================================
 *
 * Copyright 2000-2002 bob mcwhirter & James Strachan.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 * 
 *   * Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 * 
 *   * Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 * 
 *   * Neither the name of the Jaxen Project nor the names of its
 *     contributors may be used to endorse or promote products derived 
 *     from this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
 * PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
 * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * ====================================================================
 * This software consists of voluntary contributions made by many 
 * individuals on behalf of the Jaxen Project and was originally 
 * created by bob mcwhirter  and 
 * James Strachan .  For more information on the 
 * Jaxen Project, please see .
 * 
 * $Id: SumFunction.java,v 1.11 2006/02/05 21:47:41 elharo Exp $
 */


package org.navimatrix.jaxen.function;

import java.util.Iterator;
import java.util.List;

import org.navimatrix.jaxen.Context;
import org.navimatrix.jaxen.Function;
import org.navimatrix.jaxen.FunctionCallException;
import org.navimatrix.jaxen.Navigator;

/**
 * 4.4 number sum(node-set) 
 * 
 * 
 * The sum function returns the sum, for each node in the argument node-set, 
 * of the result of converting the string-values of the node to a number.
 * 
 * 
 * @author bob mcwhirter (bob @ werken.com)
 * @see Section 4.4 of the XPath Specification
 */
public class SumFunction implements Function
{

    /**
     * Create a new SumFunction object.
     */
    public SumFunction() {}
    
    /** Returns the sum of its arguments.
     *
     * @param context the context at the point in the
     *         expression when the function is called
     * @param args a list that contains exactly one item, also a List
     * 
     * @return a Double containing the sum of the items in args.get(0)
     * 
     * @throws FunctionCallException if args has more or less than one item;
     *     or if the first argument is not a List
     */
    public Object call(Context context,
                       List args) throws FunctionCallException
    {

        if (args.size() == 1)
        {
            return evaluate( args.get(0),
                             context.getNavigator() );
        }

        throw new FunctionCallException( "sum() requires one argument." );
    }

    /** 
     * Returns the sum of the items in a list.
     * If necessary, each item in the list is first converted to a Double
     * as if by the XPath number() function.
     * 
     * @param obj a List of numbers to be summed
     * @param nav ignored
     * 
     * @return the sum of the list
     * 
     * @throws FunctionCallException if obj is not a List
     */
    public static Double evaluate(Object obj,
                                  Navigator nav) throws FunctionCallException
    {
        double sum  = 0;

        if (obj instanceof List)
        {
            Iterator nodeIter = ((List)obj).iterator();
            while ( nodeIter.hasNext() )
            {
                double term = NumberFunction.evaluate( nodeIter.next(),
                                                nav ).doubleValue();
                sum += term;
            }
        }
        else
        {
            throw new FunctionCallException("The argument to the sum function must be a node-set");
        }

        return new Double(sum);
    }
    
}