Class AxisExpression

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

    public final class AxisExpression
    extends ComputedExpression
    An AxisExpression is always obtained by simplifying a PathExpression. It represents a PathExpression that starts at the context node, and uses a simple node-test with no filters. For example "*", "title", "./item", "@*", or "ancestor::chapter*".

    An AxisExpression delivers nodes in axis order (not in document order). To get nodes in document order, in the case of a reverse axis, the expression should be wrapped in a Reverser.

    See Also:
    Serialized Form
    • Field Detail

      • computedCardinality

        int computedCardinality
    • Constructor Detail

      • AxisExpression

        public AxisExpression​(byte axis,
                              NodeTest nodeTest)
        Constructor
        Parameters:
        axis - The axis to be used in this AxisExpression: relevant constants are defined in class net.sf.saxon.om.Axis.
        nodeTest - The conditions to be satisfied by selected nodes. May be null, indicating that any node on the axis is acceptable
        See Also:
        Axis
    • Method Detail

      • typeCheck

        public Expression typeCheck​(StaticContext env,
                                    ItemType contextItemType)
                             throws XPathException
        Type-check the expression
        Parameters:
        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 to perform necessary run-time type checks, and to perform other type-related optimizations
        Throws:
        StaticError - if an error is discovered during this phase (typically a type error)
        XPathException
      • getContextItemType

        public ItemType getContextItemType()
        Get the static type of the context item for this AxisExpression. May be null if not known.
      • optimize

        public Expression optimize​(Optimizer opt,
                                   StaticContext env,
                                   ItemType contextItemType)
        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
      • equals

        public boolean equals​(java.lang.Object other)
        Is this expression the same as another expression?
        Overrides:
        equals in class java.lang.Object
      • hashCode

        public int hashCode()
        get HashCode for comparing two expressions
        Overrides:
        hashCode in class java.lang.Object
      • getIntrinsicDependencies

        public int getIntrinsicDependencies()
        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:
        getIntrinsicDependencies in class ComputedExpression
        Returns:
        a set of bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty
      • computeSpecialProperties

        public int computeSpecialProperties()
        Get the static properties of this expression (other than its type). The result is bit-signficant. 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
      • getItemType

        public final ItemType getItemType​(TypeHierarchy th)
        Determine the data type of the items returned by this expression
        Parameters:
        th -
        Returns:
        Type.NODE or a subtype, based on the NodeTest in the axis step, plus information about the content type if this is known from schema analysis
      • getAxis

        public byte getAxis()
        Get the axis
      • getNodeTest

        public NodeTest getNodeTest()
        Get the NodeTest. Returns null if the AxisExpression can return any node.
      • display

        public void display​(int level,
                            java.io.PrintStream out,
                            Configuration config)
        Diagnostic print of expression structure
        Parameters:
        level - indentation level for this expression
        out - Output destination
      • toString

        public java.lang.String toString()
        Represent the expression as a string for diagnostics
        Overrides:
        toString in class java.lang.Object
      • toString

        public java.lang.String toString​(NamePool pool)
        Represent the expression as a string for diagnostics