Class Empty

java.lang.Object
net.sf.saxon.expr.Expression
net.sf.saxon.expr.FunctionCall
net.sf.saxon.functions.SystemFunction
net.sf.saxon.functions.Aggregate
net.sf.saxon.functions.Empty
All Implemented Interfaces:
Serializable, SourceLocator, LocationProvider, SaxonLocator, InstructionInfo, Locator
public class Empty extends Aggregate
Implementation of the fn:exists function
See Also:

  • Constructor Details

    • Empty

      public Empty()

  • Method Details

    • getImplementationMethod

      public int getImplementationMethod()
      Description copied from class: SystemFunction
      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 directly. The other methods will always be available indirectly, using an implementation that relies on one of the other methods.
      Overrides:
      getImplementationMethod in class SystemFunction
      Returns:
      the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

    • isNegatable

      public boolean isNegatable(ExpressionVisitor visitor)
      Check whether this specific instance of the expression is negatable
      Returns:
      true if it is

    • negate

      public Expression negate()
      Return the negation of the expression
      Returns:
      the negation of the expression

    • optimize

      public Expression optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) throws XPathException
      Perform optimisation of an expression and its subexpressions.

      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 SystemFunction
      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)

    • evaluateItem

      public Item evaluateItem(XPathContext context) throws XPathException
      Evaluate the function
      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

    • effectiveBooleanValue

      public boolean effectiveBooleanValue(XPathContext c) throws XPathException
      Evaluate the function in a boolean context
      Overrides:
      effectiveBooleanValue in class Expression
      Parameters:
      c - The context in which the expression is to be evaluated
      Returns:
      the effective boolean value
      Throws:
      XPathException - if any dynamic error occurs evaluating the expression