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## net.sf.saxon.xpath
Class XPathExpressionImpl

    java.lang.Object
      net.sf.saxon.xpath.XPathExpressionImpl

All Implemented Interfaces:
  XPathExpression, SortKeyEvaluator

    public class XPathExpressionImpl

extends Object
implements XPathExpression, SortKeyEvaluator

The JAXP XPathExpression interface represents a compiled XPath expression that can be repeatedly evaluated. This class is Saxon's implementation of that interface.

The class also includes some methods retained from Saxon's original XPath API. When these methods are used, the object contains the context node and other state, so it is not thread-safe.

Author:
  Michael H. Kay

Method Summary
`List` | `evaluate()` Execute a prepared XPath expression, returning the results as a List.
`String` | `evaluate(InputSource inputSource)` Evaluate the XPath expression against an input source to obtain a string result
`Object` | `evaluate(InputSource inputSource, QName qName)` Evaluate the XPath expression against an input source to obtain a result of a specified type
`String` | `evaluate(Object node)` Evaluate the expression to return a string value
`Object` | `evaluate(Object node, QName qName)` JAXP 1.3 evaluate() method
`Object` | `evaluateSingle()` Execute a prepared XPath expression, returning the first item in the result.
`Item` | `evaluateSortKey(int n, XPathContext c)` Callback for evaluating the sort keys.
`Configuration` | `getConfiguration()` Get the Configuration under which this XPath expression was compiled
`Expression` | `getInternalExpression()` Low-level method to get the internal Saxon expression object.
`SlotManager` | `getStackFrameMap()` Get the stack frame map.
`SequenceIterator` | `rawIterator()` Get a raw iterator over the results of the expression.
`void` | `setContextNode(NodeInfo node)` Set the context node for evaluating the expression.
`void` | `setSortKey(XPathExpressionImpl sortKey)` Define the sort order for the results of the expression.

Methods inherited from class java.lang.Object
`equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Method Detail

### getStackFrameMap

    public SlotManager getStackFrameMap()

  Get the stack frame map. This holds information about the allocation of slots to variables. This is needed by applications using low-level interfaces for evaluating the expression

### getConfiguration

    public Configuration getConfiguration()

  Get the Configuration under which this XPath expression was compiled

### setSortKey

    public void setSortKey(XPathExpressionImpl sortKey)

  Define the sort order for the results of the expression. If this method is called, then the list returned by a subsequent call on the evaluate() method will first be sorted.

  Parameters:
    `sortKey` - an XPathExpression, which will be applied to each item in the sequence; the result of this expression determines the ordering of the list returned by the evaluate() method. The sortKey can be null, to clear a previous sort key.

### setContextNode

    public void setContextNode(NodeInfo node)

  Set the context node for evaluating the expression. If this method is not called, the context node will be the root of the document to which the prepared expression is bound.

### evaluate

    public List evaluate()
                  throws XPathException

  Execute a prepared XPath expression, returning the results as a List. The context node must have been set previously using `setContextNode(net.sf.saxon.om.NodeInfo)`.

  Returns:
    The results of the expression, as a List. The List represents the sequence of items returned by the expression. Each item in the list will either be an instance of net.sf.saxon.om.NodeInfo, representing a node, or a Java object representing an atomic value. For the types of Java object that may be returned, see `evaluate(Object, javax.xml.namespace.QName)` with the second argument set to NODESET.
  Throws:
    `XPathException`

### evaluateSingle

    public Object evaluateSingle()
                          throws XPathException

  Execute a prepared XPath expression, returning the first item in the result. This is useful where it is known that the expression will only return a singleton value (for example, a single node, or a boolean). The context node must be set previously using `setContextNode(net.sf.saxon.om.NodeInfo)`.

  Returns:
    The first item in the sequence returned by the expression. If the expression returns an empty sequence, this method returns null. Otherwise, it returns the first item in the result sequence, represented as a Java object using the same mapping as for the evaluate() method
  Throws:
    `XPathException`

### rawIterator

    public SequenceIterator rawIterator()
                                 throws XPathException

  Get a raw iterator over the results of the expression. This returns results without any conversion of the returned items to "native" Java classes. This method is intended for use by applications that need to process the results of the expression using internal Saxon interfaces.

  Throws:
    `XPathException`

### evaluate

    public Object evaluate(Object node,
                           QName qName)
                    throws XPathExpressionException

  JAXP 1.3 evaluate() method

  Specified by:
    `evaluate` in interface `XPathExpression`
  Parameters:
    `node` - The context node. This must use a representation of nodes that this implementation understands. This may be a Saxon NodeInfo, or a node in one of the external object models supported, for example DOM, DOM4J, JDOM, or XOM, provided the support module for that object model is loaded.

    Contrary to the interface specification, Saxon does not supply an empty document when the value is null. This is because Saxon supports multiple object models, and it's unclear what kind of document node would be appropriate. Instead, Saxon uses the node supplied to the `setContextNode(net.sf.saxon.om.NodeInfo)` method if available, and if none is available, executes the XPath expression with the context item undefined.

    Saxon does not allow a NodeList to be supplied for this parameter. It's not clear what this would be intended to mean.

    `qName` - Indicates the type of result required. This must be one of the constants defined in the JAXP `XPathConstants` class. Saxon will attempt to convert the actual result of the expression to the required type using the XPath 1.0 conversion rules.
  Returns:
    the result of the evaluation, as a Java object of the appropriate type. Saxon interprets the rules as follows:

    QName | Return Value
    BOOLEAN | The effective boolean value of the actual result, as a Java Boolean object
    STRING | The result of applying the string() function to the actual result, as a Java String object
    NUMBER | The result of applying the number() function to the actual result, as a Java Double object
    NODE | A single node, in the native data model supplied as input. If the expression returns more than one node, the first is returned. If the expression returns an empty sequence, null is returned. If the expression returns an atomic value, or if the first item in the result sequence is an atomic value, an exception is thrown.
    NODESET | This is interpreted as allowing any sequence, of nodes or atomic values. If the first argument is a wrapper around a DOM Node, then the result is returned as a DOM NodeList, and an exception is then thrown if the result sequence contains a value that is not a DOM Node. In all other cases the result is returned as a Java List object, unless it is empty, in which case null is returned. The contents of the list may be node objects (in the native data model supplied as input), or Java objects representing the XPath atomic values in the actual result: String for an xs:string, Double for a xs:double, Long for an xs:integer, and so on. (For safety, cast the values to a type such as xs:string within the XPath expression).

  Throws:
    `XPathExpressionException` - if evaluation of the expression fails or if the result cannot be converted to the requested type.

### evaluate

    public String evaluate(Object node)
                    throws XPathExpressionException

  Evaluate the expression to return a string value

  Specified by:
    `evaluate` in interface `XPathExpression`
  Parameters:
    `node` - the initial context node. This must be either an instance of NodeInfo or a node recognized by a known external object model.

    Contrary to the interface specification, Saxon does not supply an empty document when the value is null. This is because Saxon supports multiple object models, and it's unclear what kind of document node would be appropriate. Instead, Saxon uses the node supplied to the `setContextNode(net.sf.saxon.om.NodeInfo)` method if available, and if none is available, executes the XPath expression with the context item undefined.

  Returns:
    the results of the expression, converted to a String
  Throws:
    `XPathExpressionException` - if evaluation fails

### evaluate

    public Object evaluate(InputSource inputSource,
                           QName qName)
                    throws XPathExpressionException

  Evaluate the XPath expression against an input source to obtain a result of a specified type

  Specified by:
    `evaluate` in interface `XPathExpression`
  Parameters:
    `inputSource` - The input source document against which the expression is evaluated. (Note that there is no caching. This will be parsed, and the parsed result will be discarded.) If the supplied value is null then (contrary to the JAXP specifications), the XPath expression is evaluated with the context item undefined.
    `qName` - The type required, identified by a constant in `XPathConstants`
  Returns:
    the result of the evaluation, as a Java object of the appropriate type: see `evaluate(Object, javax.xml.namespace.QName)`
  Throws:
    `XPathExpressionException`

### evaluate

    public String evaluate(InputSource inputSource)
                    throws XPathExpressionException

  Evaluate the XPath expression against an input source to obtain a string result

  Specified by:
    `evaluate` in interface `XPathExpression`
  Parameters:
    `inputSource` - The input source document against which the expression is evaluated. (Note that there is no caching. This will be parsed, and the parsed result will be discarded.)
  Returns:
    the result of the evaluation, converted to a String
  Throws:
    `XPathExpressionException` - in the event of an XPath dynamic error
    `NullPointerException` - If `inputSource` is `null`.

### evaluateSortKey

    public Item evaluateSortKey(int n,
                                XPathContext c)
                         throws XPathException

  Callback for evaluating the sort keys. For internal use only.

  Specified by:
    `evaluateSortKey` in interface `SortKeyEvaluator`
  Throws:
    `XPathException`

### getInternalExpression

    public Expression getInternalExpression()

  Low-level method to get the internal Saxon expression object. This exposes a wide range of internal methods that may be needed by specialized applications, and allows greater control over the dynamic context for evaluating the expression.

  Returns:
    the underlying Saxon expression object.

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Copyright (C) Michael H. Kay. All rights reserved.