/*

 * Copyright 2003-2005 Sun Microsystems, Inc.  All Rights Reserved.

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

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 */

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>

 * @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);

}