/*
* $Header: /home/projects/jaxen/scm/jaxen/src/java/main/org/jaxen/function/BooleanFunction.java,v 1.17 2006/02/05 21:47:41 elharo Exp $
* $Revision: 1.17 $
* $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 <bob@werken.com> and
* James Strachan <jstrachan@apache.org>. For more information on the
* Jaxen Project, please see <http://www.jaxen.org/>.
*
* $Id: BooleanFunction.java,v 1.17 2006/02/05 21:47:41 elharo Exp $
*/
package org.orbeon.jaxen.function;
import org.orbeon.jaxen.Context;
import org.orbeon.jaxen.Function;
import org.orbeon.jaxen.FunctionCallException;
import org.orbeon.jaxen.Navigator;
import java.util.List;
/**
* <p>
* <b>4.3</b> <code><i>boolean</i> boolean(<i>object</i>)</code>
* </p>
*
* <blockquote
* src="http://www.w3.org/TR/xpath#section-Boolean-Functions">
* <p>
* The <b><a href="http://www.w3.org/TR/xpath#function-boolean" target="_top">boolean</a></b>
* function converts its argument to a boolean as follows:
* </p>
*
* <ul>
*
* <li>
* <p>
* a number is true if and only if it is neither positive or negative
* zero nor NaN
* </p>
* </li>
*
* <li>
* <p>
* a node-set is true if and only if it is non-empty
* </p>
* </li>
*
* <li>
* <p>
* a string is true if and only if its length is non-zero
* </p>
* </li>
*
* <li>
*
* <p>
* an object of a type other than the four basic types is converted to a
* boolean in a way that is dependent on that type
* </p></li></ul>
* </blockquote>
*
* @author bob mcwhirter (bob @ werken.com)
* @see <a href="http://www.w3.org/TR/xpath#function-boolean">Section 4.3 of the XPath Specification</a>
*/
public class BooleanFunction implements Function
{
/**
* Create a new <code>BooleanFunction</code> object.
*/
public BooleanFunction() {}
/** Convert the argument to a <code>Boolean</code>
*
* @param context the context at the point in the
* expression when the function is called
* @param args a list with exactly one item which will be converted to a
* <code>Boolean</code>
*
* @return the result of evaluating the function;
* <code>Boolean.TRUE</code> or <code>Boolean.FALSE</code>
*
* @throws FunctionCallException if <code>args</code> has more or less than one item
*/
public Object call(Context context,
List args) throws FunctionCallException
{
if ( args.size() == 1 )
{
return evaluate( args.get(0), context.getNavigator() );
}
throw new FunctionCallException("boolean() requires one argument");
}
/**
* <p>Convert the argument <code>obj</code> to a <code>Boolean</code>
* according to the following rules:</p>
*
* <ul>
* <li>Lists are false if they're empty; true if they're not.</li>
* <li>Booleans are false if they're false; true if they're true.</li>
* <li>Strings are false if they're empty; true if they're not.</li>
* <li>Numbers are false if they're 0 or NaN; true if they're not.</li>
* <li>All other objects are true.</li>
* </ul>
*
* @param obj the object to convert to a boolean
* @param nav ignored
*
* @return <code>Boolean.TRUE</code> or <code>Boolean.FALSE</code>
*/
public static Boolean evaluate(Object obj, Navigator nav)
{
if ( obj instanceof List )
{
List list = (List) obj;
// if it's an empty list, then we have a null node-set -> false
if (list.size() == 0)
{
return Boolean.FALSE;
}
// otherwise, unwrap the list and check the primitive
obj = list.get(0);
}
// now check for primitive types
// otherwise a non-empty node-set is true
// if it's a Boolean, let it decide
if ( obj instanceof Boolean )
{
return (Boolean) obj;
}
// if it's a Number, != 0 -> true
else if ( obj instanceof Number )
{
double d = ((Number) obj).doubleValue();
if ( d == 0 || Double.isNaN(d) )
{
return Boolean.FALSE;
}
return Boolean.TRUE;
}
// if it's a String, "" -> false
else if ( obj instanceof String )
{
return ( ((String)obj).length() > 0
? Boolean.TRUE
: Boolean.FALSE );
}
else
{
// assume it's a node so that this node-set is non-empty
// and so it's true
return ( obj != null ) ? Boolean.TRUE : Boolean.FALSE;
}
}
}