Class ItemChecker

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

public final class ItemChecker extends UnaryExpression
A ItemChecker implements the item type checking of "treat as": that is, it returns the supplied sequence, checking that all its items are of the correct type
See Also:
  • Constructor Details

    • ItemChecker

      public ItemChecker(Expression sequence, ItemType itemType, RoleLocator role)
      Constructor
      Parameters:
      sequence - the expression whose value we are checking
      itemType - the required type of the items in the sequence
      role - information used in constructing an error message
  • Method Details

    • getRequiredType

      public ItemType getRequiredType()
      Get the required type
      Returns:
      the required type of the items in the sequence
    • getRoleLocator

      public RoleLocator getRoleLocator()
      Get the RoleLocator (used to construct error messages)
      Returns:
      the RoleLocator
    • simplify

      public Expression simplify(ExpressionVisitor visitor) throws XPathException
      Simplify an expression
      Overrides:
      simplify in class UnaryExpression
      Parameters:
      visitor - an 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
      Type-check the expression
      Overrides:
      typeCheck in class UnaryExpression
      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)
    • getImplementationMethod

      public int getImplementationMethod()
      An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided. This implementation provides both iterate() and process() methods natively.
      Overrides:
      getImplementationMethod in class Expression
      Returns:
      the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD
    • iterate

      public SequenceIterator iterate(XPathContext context) throws XPathException
      Iterate over the sequence of values
      Specified by:
      iterate in interface SequenceIterable
      Overrides:
      iterate in class Expression
      Parameters:
      context - supplies the context for evaluation
      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
    • evaluateItem

      public Item evaluateItem(XPathContext context) throws XPathException
      Evaluate as an Item.
      Specified by:
      evaluateItem in interface EvaluableItem
      Overrides:
      evaluateItem in class Expression
      Parameters:
      context - The context in which the expression is to be evaluated
      Returns:
      the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence
      Throws:
      XPathException - if any dynamic error occurs evaluating the expression
    • process

      public void process(XPathContext context) throws XPathException
      Process the instruction, without returning any tail calls
      Overrides:
      process in class Expression
      Parameters:
      context - The dynamic context, giving access to the current node, the current variables, etc.
      Throws:
      XPathException
    • copy

      public Expression copy()
      Copy an expression. This makes a deep copy.
      Specified by:
      copy in class Expression
      Returns:
      the copy of the original expression
    • getItemType

      public ItemType getItemType(TypeHierarchy th)
      Determine the data type of the items returned by the expression
      Overrides:
      getItemType in class UnaryExpression
      Parameters:
      th - the type hierarchy cache
      Returns:
      the item type of the items in the result sequence, insofar as this is known statically.
    • equals

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

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