Class PathExpression

All Implemented Interfaces:
Serializable, SourceLocator, LocationProvider, SaxonLocator, ContextMappingFunction, EvaluableItem, SequenceIterable, InstructionInfo, Locator

public final class PathExpression extends SlashExpression implements ContextMappingFunction
An expression that establishes a set of nodes by following relationships between nodes in the document. Specifically, it consists of a start expression which defines a set of nodes, and a step which defines a relationship to be followed from those nodes to create a new set of nodes.

This class inherits from SlashExpression; it is used in the common case where the SlashExpression is known to return nodes rather than atomic values.

This class is not responsible for sorting the results into document order or removing duplicates. That is done by a DocumentSorter expression which is wrapped around the path expression. However, this class does contain the logic for deciding statically whether the DocumentSorter is needed or not.

See Also:
  • Constructor Details

    • PathExpression

      public PathExpression(Expression start, Expression step)
      Constructor
      Parameters:
      start - A node-set expression denoting the absolute or relative set of nodes from which the navigation path should start.
      step - The step to be followed from each node in the start expression to yield a new node-set
  • Method Details

    • isHybrid

      public boolean isHybrid()
      Description copied from class: SlashExpression
      Determine whether this expression is capable (as far as static analysis is concerned) of returning a mixture of nodes and atomic values. If so, this needs to be prevented at run time
      Overrides:
      isHybrid in class SlashExpression
      Returns:
      true if the static type allows both nodes and atomic values
    • simplify

      public Expression simplify(ExpressionVisitor visitor) throws XPathException
      Simplify an expression
      Overrides:
      simplify in class SlashExpression
      Parameters:
      visitor - the expression visitor
      Returns:
      the simplified expression
      Throws:
      XPathException - if an error is discovered during expression rewriting
    • typeCheck

      public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException
      Perform type analysis
      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, ItemType contextItemType) throws XPathException
      Optimize the expression and perform type analysis
      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)
    • promote

      public Expression promote(PromotionOffer offer) throws XPathException
      Promote this expression if possible
      Overrides:
      promote in class SlashExpression
      Parameters:
      offer - details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression
      Returns:
      if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression
      Throws:
      XPathException - if any error is detected
    • copy

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

      public int computeSpecialProperties()
      Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.
      Overrides:
      computeSpecialProperties in class SlashExpression
      Returns:
      the special properties, as a bit-significant integer
    • getFirstStep

      public Expression getFirstStep()
      Get the first step in this expression. A path expression A/B/C is represented as (A/B)/C, but the first step is A
      Returns:
      the first step in the expression, after expanding any nested path expressions
    • getRemainingSteps

      public Expression getRemainingSteps()
      Get all steps after the first. This is complicated by the fact that A/B/C is represented as ((A/B)/C; we are required to return B/C
      Returns:
      a path expression containing all steps in this path expression other than the first, after expanding any nested path expressions
    • getLastStep

      public Expression getLastStep()
      Get the last step of the path expression
      Returns:
      the last step in the expression, after expanding any nested path expressions
    • getLeadingSteps

      public Expression getLeadingSteps()
      Get a path expression consisting of all steps except the last
      Returns:
      a path expression containing all steps in this path expression other than the last, after expanding any nested path expressions
    • isAbsolute

      public boolean isAbsolute(TypeHierarchy th)
      Test whether a path expression is an absolute path - that is, a path whose first step selects a document node
      Parameters:
      th - the type hierarchy cache
      Returns:
      true if the first step in this path expression selects a document node
    • tryToMakeAbsolute

      public PathExpression tryToMakeAbsolute(TypeHierarchy th)
      Test whether a path expression is an absolute path - that is, a path whose first step selects a document node; if not, see if it can be converted to an absolute path. This is possible in cases where the path expression has the form a/b/c and it is known that the context item is a document node; in this case it is safe to change the path expression to /a/b/c
      Parameters:
      th - the type hierarchy cache
      Returns:
      the path expression if it is absolute; the converted path expression if it can be made absolute; or null if neither condition applies.
    • addToPathMap

      public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
      Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.
      Overrides:
      addToPathMap in class Expression
      Parameters:
      pathMap - the PathMap to which the expression should be added
      pathMapNodeSet -
      Returns:
      the pathMapNode representing the focus established by this expression, in the case where this expression is the first operand of a path expression or filter expression
    • iterate

      public SequenceIterator iterate(XPathContext context) throws XPathException
      Iterate the path-expression in a given context
      Specified by:
      iterate in interface SequenceIterable
      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
    • toString

      public String toString()
      The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax
      Overrides:
      toString in class Expression
    • explain

      public void explain(ExpressionPresenter destination)
      Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
      Overrides:
      explain in class SlashExpression
      Parameters:
      destination - the expression presenter used to display the structure