Package net.sf.saxon.expr

Class AxisExpression

java.lang.Object
net.sf.saxon.expr.Expression
net.sf.saxon.expr.AxisExpression
All Implemented Interfaces:
Serializable, SourceLocator, LocationProvider, SaxonLocator, EvaluableItem, SequenceIterable, InstructionInfo, Locator
public final class AxisExpression extends Expression
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 call on reverse().

See Also:

  • Constructor Details

    • 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:

  • Method Details

    • simplify

      public Expression simplify(ExpressionVisitor visitor)
      Simplify an expression
      Overrides:
      simplify in class Expression
      Parameters:
      visitor - an expression visitor
      Returns:
      the simplified expression

    • typeCheck

      public Expression typeCheck(ExpressionVisitor visitor, ItemType 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

    • optimize

      public Expression optimize(ExpressionVisitor visitor, 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.

      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

    • equals

      public boolean equals(Object other)
      Is this expression the same as another expression?
      Overrides:
      equals in class Object

    • hashCode

      public int hashCode()
      get HashCode for comparing two expressions
      Overrides:
      hashCode in class 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 Expression
      Returns:
      a set of bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty

    • 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

    • computeCardinality

      public final int computeCardinality()
      Specify that the expression returns a singleton
      Specified by:
      computeCardinality in class Expression
      Returns:
      the computed cardinality, as one of the values StaticProperty.ALLOWS_ZERO_OR_ONE, StaticProperty.EXACTLY_ONE, StaticProperty.ALLOWS_ONE_OR_MORE, StaticProperty.ALLOWS_ZERO_OR_MORE

    • 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

    • iterate

      public SequenceIterator iterate(XPathContext context) throws XPathException
      Evaluate the path-expression in a given context to return a NodeSet
      Specified by:
      iterate in interface SequenceIterable
      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 String toString()
      Represent the expression as a string for diagnostics
      Overrides:
      toString in class Expression

    • toString

      public 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