/*
 * The contents of this file are subject to the terms
 * of the Common Development and Distribution License
 * (the "License").  You may not use this file except
 * in compliance with the License.
 *
 * You can obtain a copy of the license at
 * https://jaxp.dev.java.net/CDDLv1.0.html.
 * See the License for the specific language governing
 * permissions and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL
 * HEADER in each file and include the License file at
 * https://jaxp.dev.java.net/CDDLv1.0.html
 * If applicable add the following below this CDDL HEADER
 * with the fields enclosed by brackets "[]" replaced with
 * your own identifying information: Portions Copyright
 * [year] [name of copyright owner]
 */

/*
 * $Id: XMLEntityReader.java,v 1.3 2005/11/03 17:02:21 jeffsuttor Exp $
 * @(#)XPathFunctionResolver.java	1.14 05/11/17
 *
 * Copyright 2006 Sun Microsystems, Inc. All Rights Reserved.
 */

package javax.xml.xpath;

import javax.xml.namespace.QName;

/**
 * <p><code>XPathFunctionResolver</code> provides access to the set of user defined <code>XPathFunction</code>s.</p>
 *
 * <p>XPath functions are resolved by name and arity.
 * The resolver is not needed for XPath built-in functions and the resolver
 * <strong><em>cannot</em></strong> be used to override those functions.</p>
 *
 * <p>In particular, the resolver is only called for functions in an another
 * namespace (functions with an explicit prefix). This means that you cannot
 * use the <code>XPathFunctionResolver</code> to implement specifications
 * like <a href="http://www.w3.org/TR/xmldsig-core/">XML-Signature Syntax
 * and Processing</a> which extend the function library of XPath 1.0 in the
 * same namespace. This is a consequence of the design of the resolver.</p>
 *
 * <p>If you wish to implement additional built-in functions, you will have to
 * extend the underlying implementation directly.</p>
 *
 * @author  <a href="mailto:Norman.Walsh@Sun.com">Norman Walsh</a>
 * @author  <a href="mailto:Jeff.Suttor@Sun.com">Jeff Suttor</a>
 * @version $Revision: 1.2 $, $Date: 2005/06/10 03:50:45 $
 * @see <a href="http://www.w3.org/TR/xpath#corelib">XML Path Language (XPath) Version 1.0, Core Function Library</a>
 * @since 1.5
 */
public interface XPathFunctionResolver {
  /** 
   * <p>Find a function in the set of available functions.</p>
   * 
   * <p>If <code>functionName</code> or <code>arity</code> is <code>null</code>, then a <code>NullPointerException</code> is thrown.</p>
   *
   * @param functionName The function name.
   * @param arity The number of arguments that the returned function must accept.
   * 
   * @return The function or <code>null</code> if no function named <code>functionName</code> with <code>arity</code> arguments exists.
   * 
   * @throws NullPointerException If <code>functionName</code> or <code>arity</code> is <code>null</code>.
   */
  public XPathFunction resolveFunction(QName functionName, int arity);
}