# Interface XPathExpression

public interface XPathExpression
`XPathExpression` provides access to compiled XPath expressions. The XPath evaluation is affected by the factors described in the following table.

Evaluation of XPath Expressions
Factor | Behavior
--- | ---
context | The type of the context is implementation-dependent. If the value is null, the operation must have no dependency on the context, otherwise an XPathExpressionException will be thrown. For the purposes of evaluating XPath expressions, a DocumentFragment is treated like a Document node.
variables | If the expression contains a variable reference, its value will be found through the `XPathVariableResolver`. An `XPathExpressionException` is raised if the variable resolver is undefined or the resolver returns `null` for the variable. The value of a variable must be immutable through the course of any single evaluation.
functions | If the expression contains a function reference, the function will be found through the `XPathFunctionResolver`. An `XPathExpressionException` is raised if the function resolver is undefined or the function resolver returns `null` for the function.
QNames | QNames in the expression are resolved against the XPath namespace context.
result | This result of evaluating an expression is converted to an instance of the desired return type. Valid return types are defined in `XPathConstants`. Conversion to the return type follows XPath conversion rules.

An XPath expression is not thread-safe and not reentrant. In other words, it is the application's responsibility to make sure that one `XPathExpression` object is not used from more than one thread at any given time, and while the `evaluate` method is invoked, applications may not recursively call the `evaluate` method.

Since:
  1.5
See Also:
  - XML Path Language (XPath) Version 1.0, Expressions

- ## Method Summary

  Modifier and Type
  Method
  Description
  `String`
  `evaluate(Object item)`
  Evaluate the compiled XPath expression in the specified context and return the result as a `String`.
  `Object`
  `evaluate(Object item, QName returnType)`
  Evaluate the compiled XPath expression in the specified context and return the result as the specified type.
  `String`
  `evaluate(InputSource source)`
  Evaluate the compiled XPath expression in the context of the specified `InputSource` and return the result as a `String`.
  `Object`
  `evaluate(InputSource source, QName returnType)`
  Evaluate the compiled XPath expression in the context of the specified `InputSource` and return the result as the specified type.
  `default XPathEvaluationResult<?>`
  `evaluateExpression(Object item)`
  Evaluate the compiled XPath expression in the specified context.
  `default <T> T`
  `evaluateExpression(Object item, Class<T> type)`
  Evaluate the compiled XPath expression in the specified context, and return the result with the type specified through the `class type`.
  `default XPathEvaluationResult<?>`
  `evaluateExpression(InputSource source)`
  Evaluate the compiled XPath expression in the specified context.
  `default <T> T`
  `evaluateExpression(InputSource source, Class<T> type)`
  Evaluate the compiled XPath expression in the specified context, and return the result with the type specified through the `class type`

- ## Method Details

  - ### evaluate

    Object evaluate(Object item, QName returnType) throws XPathExpressionException
    Evaluate the compiled XPath expression in the specified context and return the result as the specified type.

    See Evaluation of XPath Expressions for context item evaluation, variable, function and QName resolution and return type conversion.

    The parameter `item` represents the context the XPath expression will be operated on. The type of the context is implementation-dependent. If the value is `null`, the operation must have no dependency on the context, otherwise an XPathExpressionException will be thrown.

    Implementation Note:
      The type of the context is usually `Node`.
    Parameters:
      `item` - The context the XPath expression will be evaluated in.
      `returnType` - The result type expected to be returned by the XPath expression.
    Returns:
      The `Object` that is the result of evaluating the expression and converting the result to `returnType`.
    Throws:
      `XPathExpressionException` - If the expression cannot be evaluated.
      `IllegalArgumentException` - If `returnType` is not one of the types defined in `XPathConstants`.
      `NullPointerException` - If `returnType` is `null`.

  - ### evaluate

    String evaluate(Object item) throws XPathExpressionException
    Evaluate the compiled XPath expression in the specified context and return the result as a `String`.

    This method calls `evaluate(Object item, QName returnType)` with a `returnType` of `XPathConstants.STRING`.

    See Evaluation of XPath Expressions for context item evaluation, variable, function and QName resolution and return type conversion.

    The parameter `item` represents the context the XPath expression will be operated on. The type of the context is implementation-dependent. If the value is `null`, the operation must have no dependency on the context, otherwise an XPathExpressionException will be thrown.

    Implementation Note:
      The type of the context is usually `Node`.
    Parameters:
      `item` - The context the XPath expression will be evaluated in.
    Returns:
      The result of evaluating an XPath expression as a `String`.
    Throws:
      `XPathExpressionException` - If the expression cannot be evaluated.

  - ### evaluate

    Object evaluate(InputSource source, QName returnType) throws XPathExpressionException
    Evaluate the compiled XPath expression in the context of the specified `InputSource` and return the result as the specified type.

    This method builds a data model for the `InputSource` and calls `evaluate(Object item, QName returnType)` on the resulting document object.

    See Evaluation of XPath Expressions for context item evaluation, variable, function and QName resolution and return type conversion.

    If `returnType` is not one of the types defined in `XPathConstants`, then an `IllegalArgumentException` is thrown.

    If `source` or `returnType` is `null`, then a `NullPointerException` is thrown.

    Parameters:
      `source` - The `InputSource` of the document to evaluate over.
      `returnType` - The desired return type.
    Returns:
      The `Object` that is the result of evaluating the expression and converting the result to `returnType`.
    Throws:
      `XPathExpressionException` - If the expression cannot be evaluated.
      `IllegalArgumentException` - If `returnType` is not one of the types defined in `XPathConstants`.
      `NullPointerException` - If `source or returnType` is `null`.

  - ### evaluate

    String evaluate(InputSource source) throws XPathExpressionException
    Evaluate the compiled XPath expression in the context of the specified `InputSource` and return the result as a `String`.

    This method calls `evaluate(InputSource source, QName returnType)` with a `returnType` of `XPathConstants.STRING`.

    See Evaluation of XPath Expressions for context item evaluation, variable, function and QName resolution and return type conversion.

    If `source` is `null`, then a `NullPointerException` is thrown.

    Parameters:
      `source` - The `InputSource` of the document to evaluate over.
    Returns:
      The `String` that is the result of evaluating the expression and converting the result to a `String`.
    Throws:
      `XPathExpressionException` - If the expression cannot be evaluated.
      `NullPointerException` - If `source` is `null`.

  - ### evaluateExpression

    default <T> T evaluateExpression(Object item, Class<T> type) throws XPathExpressionException
    Evaluate the compiled XPath expression in the specified context, and return the result with the type specified through the `class type`.

    The parameter `item` represents the context the XPath expression will be operated on. The type of the context is implementation-dependent. If the value is `null`, the operation must have no dependency on the context, otherwise an XPathExpressionException will be thrown.

    Implementation Requirements:
      The default implementation in the XPath API is equivalent to:

              (T)evaluate(item, XPathEvaluationResult.XPathResultType.getQNameType(type));

      Since the `evaluate` method does not support the `ANY` type, specifying XPathEvaluationResult as the type will result in IllegalArgumentException. Any implementation supporting the `ANY` type must override this method.
    Implementation Note:
      The type of the context is usually `Node`.
    Type Parameters:
      `T` - The class type that will be returned by the XPath expression.
    Parameters:
      `item` - The context the XPath expression will be evaluated in.
      `type` - The class type expected to be returned by the XPath expression, must be one of the types described in section 3.2 Class types in the package summary.
    Returns:
      The result of evaluating the expression.
    Throws:
      `XPathExpressionException` - If the expression cannot be evaluated.
      `IllegalArgumentException` - If `type` is not of the types corresponding to the types defined in the `XPathResultType`, or XPathEvaluationResult is specified as the type but an implementation supporting the `ANY` type is not available.
      `NullPointerException` - If `type` is `null`.
    Since:
      9

  - ### evaluateExpression

    default XPathEvaluationResult<?> evaluateExpression(Object item) throws XPathExpressionException
    Evaluate the compiled XPath expression in the specified context. This is equivalent to calling `evaluateExpression(Object item, Class type)` with type `XPathEvaluationResult`:

            evaluateExpression(item, XPathEvaluationResult.class);

    The parameter `item` represents the context the XPath expression will be operated on. The type of the context is implementation-dependent. If the value is `null`, the operation must have no dependency on the context, otherwise an XPathExpressionException will be thrown.

    Implementation Requirements:
      The default implementation in the XPath API is equivalent to:

              evaluateExpression(item, XPathEvaluationResult.class);

      Since the `evaluate` method does not support the `ANY` type, the default implementation of this method will always throw an IllegalArgumentException. Any implementation supporting the `ANY` type must therefore override this method.
    Implementation Note:
      The type of the context is usually `Node`.
    Parameters:
      `item` - The context the XPath expression will be evaluated in.
    Returns:
      The result of evaluating the expression.
    Throws:
      `XPathExpressionException` - If the expression cannot be evaluated.
      `IllegalArgumentException` - If the implementation of this method does not support the `ANY` type.
    Since:
      9

  - ### evaluateExpression

    default <T> T evaluateExpression(InputSource source, Class<T> type) throws XPathExpressionException
    Evaluate the compiled XPath expression in the specified context, and return the result with the type specified through the `class type`

    This method builds a data model for the `InputSource` and calls `evaluateExpression(Object item, Class type)` on the resulting document object.

    By default, the JDK's data model is `Document`.

    Implementation Requirements:
      The default implementation in the XPath API is equivalent to:

                    (T)evaluate(source, XPathEvaluationResult.XPathResultType.getQNameType(type));

      Since the `evaluate` method does not support the `ANY` type, specifying XPathEvaluationResult as the type will result in IllegalArgumentException. Any implementation supporting the `ANY` type must override this method.
    Type Parameters:
      `T` - The class type that will be returned by the XPath expression.
    Parameters:
      `source` - The `InputSource` of the document to evaluate over.
      `type` - The class type expected to be returned by the XPath expression, must be one of the types described in section 3.2 Class types in the package summary.
    Returns:
      The result of evaluating the expression.
    Throws:
      `XPathExpressionException` - If the expression cannot be evaluated.
      `IllegalArgumentException` - If `type` is not of the types corresponding to the types defined in the `XPathResultType`, or XPathEvaluationResult is specified as the type but an implementation supporting the `ANY` type is not available.
      `NullPointerException` - If `source or type` is `null`.
    Since:
      9

  - ### evaluateExpression

    default XPathEvaluationResult<?> evaluateExpression(InputSource source) throws XPathExpressionException
    Evaluate the compiled XPath expression in the specified context. This is equivalent to calling `evaluateExpression(InputSource source, Class type)` with type `XPathEvaluationResult`:

            evaluateExpression(source, XPathEvaluationResult.class);

    Implementation Requirements:
      The default implementation in the XPath API is equivalent to:

              (XPathEvaluationResult)evaluateExpression(source, XPathEvaluationResult.class);

      Since the `evaluate` method does not support the `ANY` type, the default implementation of this method will always throw an IllegalArgumentException. Any implementation supporting the `ANY` type must therefore override this method.
    Parameters:
      `source` - The `InputSource` of the document to evaluate over.
    Returns:
      The result of evaluating the expression.
    Throws:
      `XPathExpressionException` - If the expression cannot be evaluated.
      `IllegalArgumentException` - If the implementation of this method does not support the `ANY` type.
      `NullPointerException` - If `source` is `null`.
    Since:
      9