Class FilterExpression

    • Constructor Detail

      • FilterExpression

        public FilterExpression​(Expression start,
                                Expression filter)
        Constructor
        Parameters:
        start - A node-set expression denoting the absolute or relative set of nodes from which the navigation path should start.
        filter - An expression defining the filter predicate
    • Method Detail

      • getExpressionName

        public java.lang.String getExpressionName()
        Get a name identifying the kind of expression, in terms meaningful to a user.
        Overrides:
        getExpressionName in class Expression
        Returns:
        a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in explain() output displaying the expression.
      • getItemType

        public ItemType getItemType​(TypeHierarchy th)
        Get the data type of the items returned
        Specified by:
        getItemType in class Expression
        Parameters:
        th - the type hierarchy cache
        Returns:
        an integer representing the data type
      • isFilterIsPositional

        public boolean isFilterIsPositional()
        Returns:
        the boolean of filter is positional
        See Also:
        com.saxonica.bytecode.FilterExpressionCompiler
      • getControlledExpression

        public Expression getControlledExpression()
        Get the subexpression that is evaluated in the new context
        Specified by:
        getControlledExpression in interface ContextSwitchingExpression
        Returns:
        the subexpression evaluated in the context set by the controlling expression
      • getFilter

        public Expression getFilter()
        Get the filter expression
        Returns:
        the expression acting as the filter predicate
      • isPositional

        public boolean isPositional​(TypeHierarchy th)
        Determine if the filter is positional
        Parameters:
        th - the Type Hierarchy (for cached access to type information)
        Returns:
        true if the value of the filter depends on the position of the item against which it is evaluated
      • isSimpleBooleanFilter

        public boolean isSimpleBooleanFilter()
        Test if the filter always returns a singleton boolean
        Returns:
        true if the filter is a simple boolean expression
      • isIndependentNumericFilter

        public boolean isIndependentNumericFilter()
        Determine whether the filter is a simple independent numeric, that is, an expression that satisfies the following conditions: (a) its value is numeric; (b) the value does not depend on the context item or position; (c) the cardinality is zero or one.
        Returns:
        true if the filter is a numeric value that does not depend on the context item or position
      • 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 Expression
        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)
      • getIntegerBounds

        public IntegerValue[] getIntegerBounds()
        For an expression that returns an integer or a sequence of integers, get a lower and upper bound on the values of the integers that may be returned, from static analysis. The default implementation returns null, meaning "unknown" or "not applicable". Other implementations return an array of two IntegerValue objects, representing the lower and upper bounds respectively. The values UNBOUNDED_LOWER and UNBOUNDED_UPPER are used by convention to indicate that the value may be arbitrarily large. The values MAX_STRING_LENGTH and MAX_SEQUENCE_LENGTH are used to indicate values limited by the size of a string or the size of a sequence.
        Overrides:
        getIntegerBounds in class Expression
        Returns:
        the lower and upper bounds of integer values in the result, or null to indicate unknown or not applicable.
      • addToPathMap

        public PathMap.PathMapNodeSet addToPathMap​(PathMap pathMap,
                                                   PathMap.PathMapNodeSet pathMapNodeSet)
        Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.
        Overrides:
        addToPathMap in class Expression
        Parameters:
        pathMap - the PathMap to which the expression should be added
        pathMapNodeSet - the PathMapNodeSet to which the paths embodied in this expression should be added
        Returns:
        the pathMapNode representing the focus established by this expression, in the case where this expression is the first operand of a path expression or filter expression
      • iterateSubExpressions

        public java.util.Iterator<Expression> iterateSubExpressions()
        Get the immediate subexpressions of this expression
        Overrides:
        iterateSubExpressions in class Expression
        Returns:
        the subexpressions, as an array
      • iterateSameFocusSubExpressions

        public java.util.Iterator<Expression> iterateSameFocusSubExpressions()
        Get the immediate sub-expressions of this expression that are evaluated with the same focus (context item, position, and size) as the parent expression.
        Overrides:
        iterateSameFocusSubExpressions in class Expression
        Returns:
        an iterator containing those sub-expressions of this expression that are evaluated with the same focus as the parent expression
      • hasLoopingSubexpression

        public boolean hasLoopingSubexpression​(Expression child)
        Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly
        Overrides:
        hasLoopingSubexpression in class Expression
        Parameters:
        child - the immediate subexpression
        Returns:
        true if the child expression is evaluated repeatedly
      • replaceSubExpression

        public boolean replaceSubExpression​(Expression original,
                                            Expression replacement)
        Replace one subexpression by a replacement subexpression
        Overrides:
        replaceSubExpression in class Expression
        Parameters:
        original - the original subexpression
        replacement - the replacement subexpression
        Returns:
        true if the original subexpression is found
      • computeCardinality

        public int computeCardinality()
        Get the static cardinality of this expression
        Specified by:
        computeCardinality in class Expression
        Returns:
        the cardinality. The method attempts to determine the case where the filter predicate is guaranteed to select at most one item from the sequence being filtered
      • computeSpecialProperties

        public int computeSpecialProperties()
        Get the static properties of this expression (other than its type). The result is bit-significant. 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 Expression
        Returns:
        the static properties of the expression, as a bit-significant value
      • equals

        public boolean equals​(java.lang.Object other)
        Is this expression the same as another expression?
        Overrides:
        equals in class java.lang.Object
        Parameters:
        other - the expression to be compared with this one
        Returns:
        true if the two expressions are statically equivalent
      • hashCode

        public int hashCode()
        get HashCode for comparing two expressions
        Overrides:
        hashCode in class java.lang.Object
        Returns:
        the hash code
      • 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 Expression
        Returns:
        the dependencies
      • 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
      • toString

        public java.lang.String toString()
        The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax
        Overrides:
        toString in class Expression
        Returns:
        a representation of the expression as a string
      • explain

        public void explain​(ExpressionPresenter out)
        Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
        Specified by:
        explain in class Expression
        Parameters:
        out - the ExpressionPresenter to be used