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package javax.xml.xpath;

import org.xml.sax.InputSource;
import javax.xml.namespace.QName;
import javax.xml.namespace.NamespaceContext;

/**
 * <p><code>XPath</code> provides access to the XPath evaluation environment and expressions.</p>
 *
 * <a name="XPath-evaluation"/>
 * <table border="1" cellpadding="2">
 * <thead>
 * <tr>
 * <th colspan="2">Evaluation of XPath Expressions.</th>
 * </tr>
 * </thead>
 * <tbody>
 * <tr>
 * <td>context</td>
 * <td>
 * If a request is made to evaluate the expression in the absence
 * of a context item, an empty document node will be used for the context.
 * For the purposes of evaluating XPath expressions, a DocumentFragment
 * is treated like a Document node.
 * </td>
 * </tr>
 * <tr>
 * <td>variables</td>
 * <td>
 * If the expression contains a variable reference, its value will be found through the {@link XPathVariableResolver}
 * set with {@link #setXPathVariableResolver(XPathVariableResolver resolver)}.
 * An {@link XPathExpressionException} is raised if the variable resolver is undefined or
 * the resolver returns <code>null</code> for the variable.
 * The value of a variable must be immutable through the course of any single evaluation.</p>
 * </td>
 * </tr>
 * <tr>
 * <td>functions</td>
 * <td>
 * If the expression contains a function reference, the function will be found through the {@link XPathFunctionResolver}
 * set with {@link #setXPathFunctionResolver(XPathFunctionResolver resolver)}.
 * An {@link XPathExpressionException} is raised if the function resolver is undefined or
 * the function resolver returns <code>null</code> for the function.</p>
 * </td>
 * </tr>
 * <tr>
 * <td>QNames</td>
 * <td>
 * QNames in the expression are resolved against the XPath namespace context
 * set with {@link #setNamespaceContext(NamespaceContext nsContext)}.
 * </td>
 * </tr>
 * <tr>
 * <td>result</td>
 * <td>
 * This result of evaluating an expression is converted to an instance of the desired return type.
 * Valid return types are defined in {@link XPathConstants}.
 * Conversion to the return type follows XPath conversion rules.</p>
 * </td>
 * </tr>
 * </table>
 *
 * <p>An XPath object is not thread-safe and not reentrant.
 * In other words, it is the application's responsibility to make
 * sure that one {@link XPath} object is not used from
 * more than one thread at any given time, and while the <code>evaluate</code>
 * method is invoked, applications may not recursively call
 * the <code>evaluate</code> method.
 * <p>
 *
 * @author <a href="Norman.Walsh@Sun.com">Norman Walsh</a>
 * @author <a href="Jeff.Suttor@Sun.com">Jeff Suttor</a>
 * @see <a href="http://www.w3.org/TR/xpath">XML Path Language (XPath) Version 1.0</a>
 * @since 1.5
 */
public interface XPath {

 /**
 * <p>Reset this <code>XPath</code> to its original configuration.</p>
 *
 * <p><code>XPath</code> is reset to the same state as when it was created with
 * {@link XPathFactory#newXPath()}.
 * <code>reset()</code> is designed to allow the reuse of existing <code>XPath</code>s
 * thus saving resources associated with the creation of new <code>XPath</code>s.</p>
 *
 * <p>The reset <code>XPath</code> is not guaranteed to have the same {@link XPathFunctionResolver}, {@link XPathVariableResolver}
 * or {@link NamespaceContext} <code>Object</code>s, e.g. {@link Object#equals(Object obj)}.
 * It is guaranteed to have a functionally equal <code>XPathFunctionResolver</code>, <code>XPathVariableResolver</code>
 * and <code>NamespaceContext</code>.</p>
 */
 public void reset();

 /**
 * <p>Establish a variable resolver.</p>
 *
 * <p>A <code>NullPointerException</code> is thrown if <code>resolver</code> is <code>null</code>.</p>
 *
 * @param resolver Variable resolver.
 *
 * @throws NullPointerException If <code>resolver</code> is <code>null</code>.
 */
 public void setXPathVariableResolver(XPathVariableResolver resolver);

 /**
 * <p>Return the current variable resolver.</p>
 *
 * <p><code>null</code> is returned in no variable resolver is in effect.</p>
 *
 * @return Current variable resolver.
 */
 public XPathVariableResolver getXPathVariableResolver();

 /**
 * <p>Establish a function resolver.</p>
 *
 * <p>A <code>NullPointerException</code> is thrown if <code>resolver</code> is <code>null</code>.</p>
 *
 * @param resolver XPath function resolver.
 *
 * @throws NullPointerException If <code>resolver</code> is <code>null</code>.
 */
 public void setXPathFunctionResolver(XPathFunctionResolver resolver);

 /**
 * <p>Return the current function resolver.</p>
 *
 * <p><code>null</code> is returned in no function resolver is in effect.</p>
 *
 * @return Current function resolver.
 */
 public XPathFunctionResolver getXPathFunctionResolver();

 /**
 * <p>Establish a namespace context.</p>
 *
 * <p>A <code>NullPointerException</code> is thrown if <code>nsContext</code> is <code>null</code>.</p>
 *
 * @param nsContext Namespace context to use.
 *
 * @throws NullPointerException If <code>nsContext</code> is <code>null</code>.
 */
 public void setNamespaceContext(NamespaceContext nsContext);

 /**
 * <p>Return the current namespace context.</p>
 *
 * <p><code>null</code> is returned in no namespace context is in effect.</p>
 *
 * @return Current Namespace context.
 */
 public NamespaceContext getNamespaceContext();

 /**
 * <p>Compile an XPath expression for later evaluation.</p>
 *
 * <p>If <code>expression</code> contains any {@link XPathFunction}s,
 * they must be available via the {@link XPathFunctionResolver}.
 * An {@link XPathExpressionException} will be thrown if the
 * <code>XPathFunction</code>
 * cannot be resovled with the <code>XPathFunctionResolver</code>.</p>
 *
 * <p>If <code>expression</code> contains any variables, the
 * {@link XPathVariableResolver} in effect
 * <strong>at compile time</strong> will be used to resolve them.</p>
 *
 * <p>If <code>expression</code> is <code>null</code>, a <code>NullPointerException</code> is thrown.</p>
 *
 * @param expression The XPath expression.
 *
 * @return Compiled XPath expression.

 * @throws XPathExpressionException If <code>expression</code> cannot be compiled.
 * @throws NullPointerException If <code>expression</code> is <code>null</code>.
 */
 public XPathExpression compile(String expression)
 throws XPathExpressionException;

 /**
 * <p>Evaluate an <code>XPath</code> expression in the specified context and return the result as the specified type.</p>
 *
 * <p>See <a href="#XPath-evaluation">Evaluation of XPath Expressions</a> for context item evaluation,
 * variable, function and <code>QName</code> resolution and return type conversion.</p>
 *
 * <p>If <code>returnType</code> is not one of the types defined in {@link XPathConstants} (
 * {@link XPathConstants#NUMBER NUMBER},
 * {@link XPathConstants#STRING STRING},
 * {@link XPathConstants#BOOLEAN BOOLEAN},
 * {@link XPathConstants#NODE NODE} or
 * {@link XPathConstants#NODESET NODESET})
 * then an <code>IllegalArgumentException</code> is thrown.</p>
 *
 * <p>If a <code>null</code> value is provided for
 * <code>item</code>, an empty document will be used for the
 * context.
 * If <code>expression</code> or <code>returnType</code> is <code>null</code>, then a
 * <code>NullPointerException</code> is thrown.</p>
 *
 * @param expression The XPath expression.
 * @param item The starting context (a node, for example).
 * @param returnType The desired return type.
 *
 * @return Result of evaluating an XPath expression as an <code>Object</code> of <code>returnType</code>.
 *
 * @throws XPathExpressionException If <code>expression</code> cannot be evaluated.
 * @throws IllegalArgumentException If <code>returnType</code> is not one of the types defined in {@link XPathConstants}.
 * @throws NullPointerException If <code>expression</code> or <code>returnType</code> is <code>null</code>.
 */
 public Object evaluate(String expression, Object item, QName returnType)
 throws XPathExpressionException;

 /**
 * <p>Evaluate an XPath expression in the specified context and return the result as a <code>String</code>.</p>
 *
 * <p>This method calls {@link #evaluate(String expression, Object item, QName returnType)} with a <code>returnType</code> of
 * {@link XPathConstants#STRING}.</p>
 *
 * <p>See <a href="#XPath-evaluation">Evaluation of XPath Expressions</a> for context item evaluation,
 * variable, function and QName resolution and return type conversion.</p>
 *
 * <p>If a <code>null</code> value is provided for
 * <code>item</code>, an empty document will be used for the
 * context.
 * If <code>expression</code> is <code>null</code>, then a <code>NullPointerException</code> is thrown.</p>
 *
 * @param expression The XPath expression.
 * @param item The starting context (a node, for example).
 *
 * @return The <code>String</code> that is the result of evaluating the expression and
 * converting the result to a <code>String</code>.
 *
 * @throws XPathExpressionException If <code>expression</code> cannot be evaluated.
 * @throws NullPointerException If <code>expression</code> is <code>null</code>.
 */
 public String evaluate(String expression, Object item)
 throws XPathExpressionException;

 /**
 * <p>Evaluate an XPath expression in the context of the specified <code>InputSource</code>
 * and return the result as the specified type.</p>
 *
 * <p>This method builds a data model for the {@link InputSource} and calls
 * {@link #evaluate(String expression, Object item, QName returnType)} on the resulting document object.</p>
 *
 * <p>See <a href="#XPath-evaluation">Evaluation of XPath Expressions</a> for context item evaluation,
 * variable, function and QName resolution and return type conversion.</p>
 *
 * <p>If <code>returnType</code> is not one of the types defined in {@link XPathConstants},
 * then an <code>IllegalArgumentException</code> is thrown.</p>
 *
 * <p>If <code>expression</code>, <code>source</code> or <code>returnType</code> is <code>null</code>,
 * then a <code>NullPointerException</code> is thrown.</p>
 *
 * @param expression The XPath expression.
 * @param source The input source of the document to evaluate over.
 * @param returnType The desired return type.
 *
 * @return The <code>Object</code> that encapsulates the result of evaluating the expression.
 *
 * @throws XPathExpressionException If expression cannot be evaluated.
 * @throws IllegalArgumentException If <code>returnType</code> is not one of the types defined in {@link XPathConstants}.
 * @throws NullPointerException If <code>expression</code>, <code>source</code> or <code>returnType</code>
 * is <code>null</code>.
 */
 public Object evaluate(
 String expression,
 InputSource source,
 QName returnType)
 throws XPathExpressionException;

 /**
 * <p>Evaluate an XPath expression in the context of the specified <code>InputSource</code>
 * and return the result as a <code>String</code>.</p>
 *
 * <p>This method calls {@link #evaluate(String expression, InputSource source, QName returnType)} with a
 * <code>returnType</code> of {@link XPathConstants#STRING}.</p>
 *
 * <p>See <a href="#XPath-evaluation">Evaluation of XPath Expressions</a> for context item evaluation,
 * variable, function and QName resolution and return type conversion.</p>
 *
 * <p>If <code>expression</code> or <code>source</code> is <code>null</code>,
 * then a <code>NullPointerException</code> is thrown.</p>
 *
 * @param expression The XPath expression.
 * @param source The <code>InputSource</code> of the document to evaluate over.
 *
 * @return The <code>String</code> that is the result of evaluating the expression and
 * converting the result to a <code>String</code>.
 *
 * @throws XPathExpressionException If expression cannot be evaluated.
 * @throws NullPointerException If <code>expression</code> or <code>source</code> is <code>null</code>.
 */
 public String evaluate(String expression, InputSource source)
 throws XPathExpressionException;
}