Class AxisExpression

  • All Implemented Interfaces:
    java.io.Serializable, javax.xml.transform.SourceLocator, LocationProvider, SaxonLocator, InstructionInfo, org.xml.sax.Locator

    public final class AxisExpression
    extends Expression
    An AxisExpression is always obtained by simplifying a PathExpression. It represents a PathExpression that starts either at the context node or at some other singleton 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 call on reverse().

    Since 9.4, an axis expression does not necessarily select starting from the context item. This allows an expression such as $x/abcd (very common in XQuery FLWOR expressions) to be computed without creating a new context.

    See Also:
    Serialized Form
    • Constructor Detail

      • AxisExpression

        public AxisExpression​(byte axis,
                              NodeTest nodeTest)
        Constructor for an AxisExpression whose origin is the context item
        Parameters:
        axis - The axis to be used in this AxisExpression: relevant constants are defined in class 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

      • 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.
      • typeCheck

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

        public ItemType getContextItemType()
        Get the static type of the context item for this AxisExpression. May be null if not known.
        Returns:
        the statically-inferred type, or null if not known
      • 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
      • 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
      • 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 Expression
        Returns:
        the special properties, as a bit-significant integer
      • getItemType

        public final ItemType getItemType​(TypeHierarchy th)
        Determine the data type of the items returned by this expression
        Specified by:
        getItemType in class Expression
        Parameters:
        th - the type hierarchy cache
        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
      • getIntrinsicDependencies

        public int getIntrinsicDependencies()
        Determine the intrinsic dependencies of an expression, that is, those which are not derived from the dependencies of its subexpressions. For example, position() has an intrinsic dependency on the context position, while (position()+1) does not. The default implementation of the method returns 0, indicating "no dependencies".
        Overrides:
        getIntrinsicDependencies in class Expression
        Returns:
        a set of bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty
      • isSubtreeExpression

        public boolean isSubtreeExpression()
        Determine whether the expression can be evaluated without reference to the part of the context document outside the subtree rooted at the context node.
        Overrides:
        isSubtreeExpression in class Expression
        Returns:
        true if the expression has no dependencies on the context node, or if the only dependencies on the context node are downward selections using the self, child, descendant, attribute, and namespace axes.
      • getAxis

        public byte getAxis()
        Get the axis
        Returns:
        the axis number, for example Axis.CHILD
      • getNodeTest

        public NodeTest getNodeTest()
        Get the NodeTest. Returns null if the AxisExpression can return any node.
        Returns:
        the node test, or null if all nodes are returned
      • 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 -
        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
      • isContextPossiblyUndefined

        public boolean isContextPossiblyUndefined()
        Ask whether there is a possibility that the context item will be undefined
        Returns:
        true if this is a possibility
      • iterate

        public AxisIterator<? extends NodeInfo> iterate​(XPathContext context)
                                                 throws XPathException
        Evaluate the path-expression in a given context to return a NodeSet
        Overrides:
        iterate in class Expression
        Parameters:
        context - the evaluation context
        Returns:
        a SequenceIterator that can be used to iterate over the result of the expression
        Throws:
        XPathException - if any dynamic error occurs evaluating the expression
      • iterate

        public SequenceIterator iterate​(Item origin)
                                 throws XPathException
        Iterate the axis from a given starting node, without regard to context
        Parameters:
        origin - the starting node
        Returns:
        the iterator over the axis
        Throws:
        XPathException
      • explain

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

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

        public java.lang.String toString​(NamePool pool)
        Represent the expression as a string for diagnostics
        Parameters:
        pool - the name pool, used for expanding names in the node test
        Returns:
        a string representation of the expression