Class FilterExpression

  • All Implemented Interfaces:
    java.io.Serializable, javax.xml.transform.SourceLocator, Container, Expression, InstructionInfoProvider

    public final class FilterExpression
    extends ComputedExpression
    A FilterExpression contains a base expression and a filter predicate, which may be an integer expression (positional filter), or a boolean expression (qualifier)
    See Also:
    Serialized Form
    • 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

      • getItemType

        public ItemType getItemType​(TypeHierarchy th)
        Get the data type of the items returned
        Parameters:
        th -
        Returns:
        an integer representing the data type
      • getBaseExpression

        public Expression getBaseExpression()
        Get the underlying expression
        Returns:
        the expression being filtered
      • 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
      • typeCheck

        public Expression typeCheck​(StaticContext env,
                                    ItemType contextItemType)
                             throws XPathException
        Type-check the expression
        Parameters:
        env - the static context
        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 expression after type-checking (potentially modified to add run-time checks and/or conversions)
        Throws:
        StaticError - if an error is discovered during this phase (typically a type error)
        XPathException
      • optimize

        public Expression optimize​(Optimizer opt,
                                   StaticContext env,
                                   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.

        Parameters:
        opt - the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances.
        env - the static context of the expression
        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:
        StaticError - if an error is discovered during this phase (typically a type error)
        XPathException
      • replaceSubExpression

        public boolean replaceSubExpression​(Expression original,
                                            Expression replacement)
        Replace one subexpression by a replacement subexpression
        Specified by:
        replaceSubExpression in interface Container
        Overrides:
        replaceSubExpression in class ComputedExpression
        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 ComputedExpression
        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 ComputedExpression
        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
      • isIndexable

        public boolean isIndexable()
        Test whether the filter is amenable to indexing
      • 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 ComputedExpression
        Returns:
        the dependencies
      • display

        public void display​(int level,
                            java.io.PrintStream out,
                            Configuration config)
        Diagnostic print of expression structure
        Parameters:
        level - the indentation level
        out -
        config -