content: /*
   * $Header$
   * $Revision$
   * $Date$
   *
   * ====================================================================
   *
   * 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 <bob@werken.com> and 
   * James Strachan <jstrachan@apache.org>.  For more information on the 
   * Jaxen Project, please see <http://www.jaxen.org/>.
   * 
   * $Id$
   */
  
  package org.jaxen.function;
  
  import java.util.List;
  
  import org.jaxen.Context;
  import org.jaxen.Function;
  import org.jaxen.FunctionCallException;
  import org.jaxen.Navigator;
  
  /**
   * <p><b>4.3</b> <code><i>boolean</i> not(<i>boolean</i>)</code> </p>
   * 
   * 
   * <blockquote src="http://www.w3.org/TR/xpath#function-not">
   * The <b>not</b> function returns true if its argument is false, and false otherwise.
   * </blockquote>
   * 
   * @author bob mcwhirter (bob @ werken.com)
   * @see <a href="http://www.w3.org/TR/xpath#function-not" target="_top">Section 4.3 of the XPath Specification</a>
   */
  public class NotFunction implements Function
  {
  
      /**
       * Create a new <code>NotFunction</code> object.
       */
      public NotFunction() {}
      
      /**
       * Returns <code>Boolean.TRUE</code> if the boolean value of 
       * <code>args.get(0)</code> is false, and <code>Boolean.FALSE</code> otherwise.
       * The boolean value is calculated as if by the XPath <code>boolean</code>
       * function. 
       * 
       * @param context the context at the point in the
       *         expression where the function is called
       * @param args a single element list
       * 
       * @return <code>Boolean.TRUE</code> if the boolean value of 
       * <code>obj</code> is false, and <code>Boolean.FALSE</code> otherwise
       * 
       * @throws FunctionCallException if <code>args</code> does not have exactly one argument
       */
      public Object call(Context context,
                         List args) throws FunctionCallException
      {
          if (args.size() == 1)
          {
              return evaluate( args.get(0), context.getNavigator() );
          }
  
          throw new FunctionCallException( "not() requires one argument." );
      }
  
      /**
       * Returns <code>Boolean.TRUE</code> if the boolean value of 
       * <code>obj</code> is false, and <code>Boolean.FALSE</code> otherwise.
       * The boolean value is calculated as if by the XPath <code>boolean</code>
       * function. 
       * 
       * @param obj the object whose boolean value is inverted
       * @param nav the <code>Navigator</code> used to calculate the boolean value of <code>obj</code>
       * 
       * @return <code>Boolean.TRUE</code> if the boolean value of 
       * <code>obj</code> is false, and <code>Boolean.FALSE</code> otherwise
       */
      public static Boolean evaluate(Object obj, Navigator nav)
      {
          return ( ( BooleanFunction.evaluate( obj, nav ).booleanValue() )
                   ? Boolean.FALSE
                   : Boolean.TRUE
                   );
      }
      
  }