net.sf.saxon.expr

Class AxisExpression

Implemented Interfaces:
EvaluableItem, InstructionInfoProvider, SequenceIterable, Serializable, SourceLocator

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 Reverser.

Field Summary

Fields inherited from class net.sf.saxon.expr.Expression

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD, locationId, staticProperties

Constructor Summary

AxisExpression(byte axis, NodeTest nodeTest)
Constructor

Method Summary

PathMap.PathMapNodeSet
addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
Add a representation of this expression to a PathMap.
int
computeCardinality()
Specify that the expression returns a singleton
int
computeSpecialProperties()
Get the static properties of this expression (other than its type).
Expression
copy()
Copy an expression.
boolean
equals(Object other)
Is this expression the same as another expression?
void
explain(ExpressionPresenter destination)
Diagnostic print of expression structure.
byte
getAxis()
Get the axis
ItemType
getContextItemType()
Get the static type of the context item for this AxisExpression.
int
getIntrinsicDependencies()
Determine which aspects of the context the expression depends on.
ItemType
getItemType(TypeHierarchy th)
Determine the data type of the items returned by this expression
NodeTest
getNodeTest()
Get the NodeTest.
int
hashCode()
get HashCode for comparing two expressions
SequenceIterator
iterate(XPathContext context)
Evaluate the path-expression in a given context to return a NodeSet
SequenceIterator
iterate(Item origin)
Iterate the axis from a given starting node, without regard to context
Expression
optimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
Expression
simplify(ExpressionVisitor visitor)
Simplify an expression
String
toString()
Represent the expression as a string for diagnostics
String
toString(NamePool pool)
Represent the expression as a string for diagnostics
Expression
typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Type-check the expression

Methods inherited from class net.sf.saxon.expr.Expression

addToPathMap, adoptChildExpression, checkPermittedContents, computeCardinality, computeDependencies, computeSpecialProperties, computeStaticProperties, copy, display, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, explain, explain, findParentOf, getCardinality, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getItemType, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterate, iterateEvents, iterateSubExpressions, markTailFunctionCalls, optimize, process, promote, replaceSubExpression, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, simplify, staticTypeCheck, suppressValidation, toString, typeCheck, typeError

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:
Axis

Method Details

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 interface 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

computeCardinality

public final int computeCardinality()
Specify that the expression returns a singleton
Overrides:
computeCardinality in interface 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 interface Expression

copy

public Expression copy()
Copy an expression. This makes a deep copy.
Overrides:
copy in interface Expression
Returns:
the copy of the original expression

equals

public boolean equals(Object other)
Is this expression the same as another expression?

explain

public void explain(ExpressionPresenter destination)
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
Overrides:
explain in interface Expression

getAxis

public byte getAxis()
Get the axis

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

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 interface Expression

getItemType

public final ItemType getItemType(TypeHierarchy th)
Determine the data type of the items returned by this expression
Overrides:
getItemType in interface 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

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

hashCode

public int hashCode()
get HashCode for comparing two expressions

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 interface Expression
Parameters:
context - the evaluation context

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

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 interface 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

simplify

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

toString

public String toString()
Represent the expression as a string for diagnostics
Overrides:
toString in interface 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

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType contextItemType)
            throws XPathException
Type-check the expression
Overrides:
typeCheck in interface Expression