Class GeneralNodePattern

All Implemented Interfaces:
ExportAgent, Locatable, IdentityComparable, Traceable

public final class GeneralNodePattern extends Pattern
A GeneralNodePattern represents a pattern which, because of the presence of positional predicates or otherwise, can only be evaluated "the hard way", by evaluating the equivalent expression with successive ancestors of the tested node as context item.
  • Constructor Details

    • GeneralNodePattern

      public GeneralNodePattern(Expression expr, NodeTest itemType)
      Create a GeneralNodePattern
      Parameters:
      expr - the "equivalent expression"
      itemType - a type that all matched nodes must satisfy
  • Method Details

    • makeTopNodeEquivalent

      public void makeTopNodeEquivalent()
      A pattern whose first step uses the child axis is treated as using the child-or-top axis, which selects a node that is either (a) a child, or (b) a parentless element, comment, text node, or PI. We handle this by creating a variant of the equivalent expression that uses the self axis instead of child, and using this variant if matching a tree that satisfies the other conditions.
    • operands

      public Iterable<Operand> operands()
      Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression. Default implementation works off the results of iterateSubExpressions()

      If the expression is a Callable, then it is required that the order of the operands returned by this function is the same as the order of arguments supplied to the corresponding call() method.

      Overrides:
      operands in class Expression
      Returns:
      an iterator containing the sub-expressions of this expression
    • isMotionless

      public boolean isMotionless()
      Test whether a pattern is motionless, that is, whether it can be evaluated against a node without repositioning the input stream. This is a necessary condition for patterns used as the match pattern of a streamed template rule.
      Overrides:
      isMotionless in class Pattern
      Returns:
      true if the pattern is motionless, that is, if it can be evaluated against a streamed node without changing the position in the streamed input file
    • typeCheck

      public Pattern typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) throws XPathException
      Type-check the pattern, performing any type-dependent optimizations.
      Overrides:
      typeCheck in class Pattern
      Parameters:
      visitor - an expression visitor
      contextItemType - the type of the context item at the point where the pattern appears
      Returns:
      the optimised Pattern
      Throws:
      XPathException - if an error is discovered during this phase (typically a type error)
    • optimize

      public Pattern optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) throws XPathException
      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 Pattern
      Parameters:
      visitor - an expression visitor
      contextInfo - 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)
    • getDependencies

      public int getDependencies()
      Get the dependencies of the pattern. The only interesting dependencies for a pattern are dependencies on local variables or on user-defined functions. These are analyzed in those patterns containing predicates.
      Overrides:
      getDependencies in class Pattern
      Returns:
      the dependencies, as a bit-significant mask
    • bindCurrent

      public void bindCurrent(LocalBinding binding)
      Replace any calls on current() by a variable reference bound to the supplied binding
      Overrides:
      bindCurrent in class Pattern
    • allocateSlots

      public int allocateSlots(SlotManager slotManager, int nextFree)
      Allocate slots to any variables used within the pattern
      Overrides:
      allocateSlots in class Pattern
      Parameters:
      slotManager - details of the stack frame
      nextFree - the next slot that is free to be allocated @return the next slot that is free to be allocated
      Returns:
      the next slot that is free to be allocated
    • matches

      public boolean matches(Item item, XPathContext context) throws XPathException
      Determine whether the pattern matches a given item.
      Specified by:
      matches in class Pattern
      Parameters:
      item - the item to be tested
      context - The dynamic context.
      Returns:
      true if the pattern matches, else false
      Throws:
      XPathException - if an error occurs while matching the pattern
    • matchesBeneathAnchor

      public boolean matchesBeneathAnchor(NodeInfo node, NodeInfo anchor, XPathContext context) throws XPathException
      Determine whether this pattern matches a given Node within the subtree rooted at a given anchor node. This method is used when the pattern is used for streaming.
      Overrides:
      matchesBeneathAnchor in class Pattern
      Parameters:
      node - The NodeInfo representing the Element or other node to be tested against the Pattern
      anchor - The anchor node, which if present must match any AnchorPattern subpattern; may be null
      context - The dynamic context. Only relevant if the pattern uses variables, or contains calls on functions such as document() or key().
      Returns:
      true if the node matches the Pattern, false otherwise
      Throws:
      XPathException - if an error occurs while matching the pattern (the caller will usually treat this the same as a false result)
    • getUType

      public UType getUType()
      Get a UType indicating which kinds of items this Pattern can match.
      Specified by:
      getUType in class Pattern
      Returns:
      a UType indicating all the primitive types of item that the pattern can match.
    • getFingerprint

      public int getFingerprint()
      Determine the fingerprint of nodes to which this pattern applies. Used for optimisation.
      Overrides:
      getFingerprint in class Pattern
      Returns:
      the fingerprint of nodes matched by this pattern.
    • getItemType

      public ItemType getItemType()
      Get a NodeTest that all the nodes matching this pattern must satisfy
      Specified by:
      getItemType in class Pattern
      Returns:
      an ItemType, as specific as possible, which all the matching items satisfy
    • getEquivalentExpr

      public Expression getEquivalentExpr()
    • equals

      public boolean equals(Object other)
      Determine whether this pattern is the same as another pattern
      Overrides:
      equals in class Expression
      Parameters:
      other - the other object
      Returns:
      true if the other operand is an expression and if it can be determined that the two expressions are equivalent, in the sense that they will always return the same result.
    • computeHashCode

      protected int computeHashCode()
      hashcode supporting equals()
      Overrides:
      computeHashCode in class Expression
      Returns:
      a computed hash code
    • copy

      public Pattern copy(RebindingMap rebindings)
      Copy a pattern. This makes a deep copy.
      Specified by:
      copy in class Pattern
      Parameters:
      rebindings - variables that need to be re-bound
      Returns:
      the copy of the original pattern
    • export

      public void export(ExpressionPresenter presenter) throws XPathException
      Description copied from class: Expression
      Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
      Specified by:
      export in interface ExportAgent
      Specified by:
      export in class Pattern
      Parameters:
      presenter - the expression presenter used to display the structure
      Throws:
      XPathException - if the export fails, for example if an expression is found that won't work in the target environment.