/*

 * 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

 * have any questions.

 */

package javax.xml.xpath;

import javax.xml.namespace.QName;

/**

 * <p><code>XPathVariableResolver</code> provides access to the set of user defined XPath variables.</p>

 *

 * <p>The <code>XPathVariableResolver</code> and the XPath evaluator must adhere to a contract that

 * cannot be directly enforced by the API.  Although variables may be mutable,

 * that is, an application may wish to evaluate the same XPath expression more

 * than once with different variable values, in the course of evaluating any

 * single XPath expression, a variable's value <strong><em>must</em></strong>

 * not change.</p>

 *

 * @author  <a href="mailto:Norman.Walsh@Sun.com">Norman Walsh</a>

 * @author  <a href="mailto:Jeff.Suttor@Sun.com">Jeff Suttor</a>

 * @since 1.5

 */

public interface XPathVariableResolver {

  /**

   * <p>Find a variable in the set of available variables.</p>

   *

   * <p>If <code>variableName</code> is <code>null</code>, then a <code>NullPointerException</code> is thrown.</p>

   *

   * @param variableName The <code>QName</code> of the variable name.

   *

   * @return The variables value, or <code>null</code> if no variable named <code>variableName</code>

   *   exists.  The value returned must be of a type appropriate for the underlying object model.

   *

   * @throws NullPointerException If <code>variableName</code> is <code>null</code>.

   */

  public Object resolveVariable(QName variableName);

}