Class Existence

    • Constructor Detail

      • Existence

        public Existence()
    • Method Detail

      • optimize

        public Expression optimize​(ExpressionVisitor visitor,
                                   ItemType 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)
      • isNegatable

        public boolean isNegatable​(ExpressionVisitor visitor)
        Check whether this specific instance of the expression is negatable
        Specified by:
        isNegatable in interface Negatable
        Returns:
        true if it is
      • negate

        public Expression negate()
        Return the negation of the expression
        Specified by:
        negate in interface Negatable
        Returns:
        the negation of 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
      • evaluateItem

        public Item evaluateItem​(XPathContext c)
                          throws XPathException
        Evaluate in a general context
        Specified by:
        evaluateItem in interface EvaluableItem
        Overrides:
        evaluateItem in class Expression
        Parameters:
        c - 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