Class SimpleStepExpression

  • All Implemented Interfaces:
    java.io.Serializable, javax.xml.transform.SourceLocator, LocationProvider, SaxonLocator, ContextMappingFunction<Item>, ContextSwitchingExpression, InstructionInfo, org.xml.sax.Locator

    public final class SimpleStepExpression
    extends SlashExpression
    An SimpleStepExpression is a special case of a SlashExpression in which the start expression selects a single item (or nothing), and the step expression is a simple AxisExpression. This is designed to avoid the costs of creating a new dynamic context for expressions (common in XQuery) such as for $b in EXPR return $b/title
    See Also:
    Serialized Form
    • Constructor Detail

    • Method Detail

      • typeCheck

        public Expression typeCheck​(ExpressionVisitor visitor,
                                    ExpressionVisitor.ContextItemType contextItemType)
                             throws XPathException
        Description copied from class: SlashExpression
        Type-check the expression
        Overrides:
        typeCheck in class SlashExpression
        Parameters:
        visitor - an expression visitor
        contextItemType - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to Type.ITEM_TYPE
        Returns:
        the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations
        Throws:
        XPathException - if an error is discovered during this phase (typically a type error)
      • optimize

        public Expression optimize​(ExpressionVisitor visitor,
                                   ExpressionVisitor.ContextItemType contextItemType)
                            throws XPathException
        Description copied from class: Expression
        Perform optimisation of an expression and its subexpressions. This is the third and final phase of static optimization.

        This method is called after all references to functions and variables have been resolved to the declaration of the function or variable, and after all type checking has been done.

        Overrides:
        optimize in class SlashExpression
        Parameters:
        visitor - an expression visitor
        contextItemType - the static type of "." at the point where this expression is invoked. The parameter is set to null if it is known statically that the context item will be undefined. If the type of the context item is not known statically, the argument is set to Type.ITEM_TYPE
        Returns:
        the original expression, rewritten if appropriate to optimize execution
        Throws:
        XPathException - if an error is discovered during this phase (typically a type error)
      • copy

        public Expression copy()
        Copy an expression. This makes a deep copy.
        Overrides:
        copy in class SlashExpression
        Returns:
        the copy of the original expression
      • iterate

        public SequenceIterator iterate​(XPathContext context)
                                 throws XPathException
        Evaluate the expression, returning an iterator over the result
        Overrides:
        iterate in class SlashExpression
        Parameters:
        context - the evaluation context
        Returns:
        a SequenceIterator that can be used to iterate over the result of the expression
        Throws:
        XPathException - if any dynamic error occurs evaluating the expression