Class PathExpression

java.lang.Object
net.sf.saxon.expr.ComputedExpression
net.sf.saxon.expr.PathExpression
All Implemented Interfaces:
Serializable, SourceLocator, Container, ContextMappingFunction, Expression, InstructionInfoProvider

public final class PathExpression extends ComputedExpression 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.
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

    • getStartExpression

      public Expression getStartExpression()
      Get the start expression (the left-hand operand)
    • getStepExpression

      public Expression getStepExpression()
      Get the step expression (the right-hand operand)
    • getItemType

      public final ItemType getItemType(TypeHierarchy th)
      Determine the data type of the items returned by this exprssion
      Specified by:
      getItemType in interface Expression
      Parameters:
      th -
      Returns:
      the type of the step
    • simplify

      public Expression simplify(StaticContext env) throws XPathException
      Simplify an expression
      Specified by:
      simplify in interface Expression
      Overrides:
      simplify in class ComputedExpression
      Parameters:
      env - the static context
      Returns:
      the simplified expression
      Throws:
      XPathException - if an error is discovered during expression rewriting
    • typeCheck

      public Expression typeCheck(StaticContext env, ItemType contextItemType) throws XPathException
      Optimize the expression and perform type analysis
      Specified by:
      typeCheck in interface Expression
      Parameters:
      env - the static context of the expression
      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
    • optimize

      public Expression optimize(Optimizer opt, StaticContext env, ItemType contextItemType) throws XPathException
      Optimize the expression and perform type analysis
      Specified by:
      optimize in interface Expression
      Parameters:
      opt - the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances.
      env - the static context of the expression
      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
    • promote

      public Expression promote(PromotionOffer offer) throws XPathException
      Promote this expression if possible
      Specified by:
      promote in interface Expression
      Overrides:
      promote in class ComputedExpression
      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
    • iterateSubExpressions

      public Iterator iterateSubExpressions()
      Get the immediate subexpressions of this expression
      Specified by:
      iterateSubExpressions in interface Expression
      Overrides:
      iterateSubExpressions in class ComputedExpression
      Returns:
      an iterator containing the sub-expressions of this expression
    • replaceSubExpression

      public boolean replaceSubExpression(Expression original, Expression replacement)
      Replace one subexpression by a replacement subexpression
      Specified by:
      replaceSubExpression in interface Container
      Overrides:
      replaceSubExpression in class ComputedExpression
      Parameters:
      original - the original subexpression
      replacement - the replacement subexpression
      Returns:
      true if the original subexpression is found
    • computeDependencies

      public int computeDependencies()
      Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such as XPathContext.VARIABLES and XPathContext.CURRENT_NODE
      Overrides:
      computeDependencies in class ComputedExpression
      Returns:
      the depencies, as a bit-mask
    • 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 ComputedExpression
    • computeCardinality

      public int computeCardinality()
      Determine the static cardinality of the expression
      Specified by:
      computeCardinality in class ComputedExpression
    • equals

      public boolean equals(Object other)
      Is this expression the same as another expression?
      Overrides:
      equals in class Object
    • hashCode

      public int hashCode()
      get HashCode for comparing two expressions
      Overrides:
      hashCode in class Object
    • 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
    • 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
    • getLastStep

      public Expression getLastStep()
      Get the last step of the path expression
    • getLeadingSteps

      public Expression getLeadingSteps()
      Get a path expression consisting of all steps except the last
    • 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
    • iterate

      public SequenceIterator iterate(XPathContext context) throws XPathException
      Iterate the path-expression in a given context
      Specified by:
      iterate in interface Expression
      Overrides:
      iterate in class ComputedExpression
      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
    • map

      public SequenceIterator map(XPathContext context) throws XPathException
      Mapping function, from a node returned by the start iteration, to a sequence returned by the child.
      Specified by:
      map in interface ContextMappingFunction
      Parameters:
      context - The processing context. The item to be mapped is the context item identified from this context: the values of position() and last() also relate to the set of items being mapped
      Returns:
      a SequenceIterator over the sequence of items that the supplied input item maps to
      Throws:
      XPathException
    • display

      public void display(int level, PrintStream out, Configuration config)
      Diagnostic print of expression structure
      Specified by:
      display in interface Expression
      Parameters:
      level - indentation level for this expression
      out - Output destination
      config -