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* Copyright (c) 2003, 2005, Oracle and/or its affiliates. All rights reserved.
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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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);
}