net.sf.saxon.expr
Class AxisExpression

java.lang.Object
  net.sf.saxon.expr.ComputedExpression
      net.sf.saxon.expr.AxisExpression

All Implemented Interfaces:

Container, Expression, InstructionInfoProvider, java.io.Serializable, javax.xml.transform.SourceLocator

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 Summary

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

locationId, staticProperties

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

AxisExpression(byte axis, NodeTest nodeTest)
Constructor

Method Summary

int	computeCardinality() Specify that the expression returns a singleton
int	computeSpecialProperties() Get the static properties of this expression (other than its type).
void	display(int level, NamePool pool, java.io.PrintStream out) Diagnostic print of expression structure
boolean	equals(java.lang.Object other) Is this expression the same as another expression?
byte	getAxis() Get the axis
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
Expression	optimize(Optimizer opt, StaticContext env, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.
Expression	simplify(StaticContext env) Simplify an expression
java.lang.String	toString() Represent the expression as a string for diagnostics
java.lang.String	toString(NamePool pool) Represent the expression as a string for diagnostics
Expression	typeCheck(StaticContext env, ItemType contextItemType) Type-check the expression

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

adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, iterateSubExpressions, markTailFunctionCalls, process, promote, resetStaticProperties, setLocationId, setParentExpression, suppressValidation, typeError, typeError

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

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

simplify

public Expression simplify(StaticContext env)

Simplify an expression

Specified by:

simplify in interface Expression

Overrides:

simplify in class ComputedExpression

Returns:

the simplified expression

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:

XPathException

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?

hashCode

public int hashCode()

get HashCode for comparing two expressions

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

computeCardinality

public final int computeCardinality()

Specify that the expression returns a singleton

Specified by:

computeCardinality in class ComputedExpression

getAxis

public byte getAxis()

Get the axis

getNodeTest

public NodeTest getNodeTest()

Get the NodeTest. Returns null if the AxisExpression can return any node.

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 Expression

Overrides:

iterate in class ComputedExpression

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

display

public void display(int level,
                    NamePool pool,
                    java.io.PrintStream out)

Diagnostic print of expression structure

Parameters:

level - indentation level for this expression

pool - NamePool used to expand any names appearing in the expression

out - Output destination

toString

public java.lang.String toString()

Represent the expression as a string for diagnostics

toString

public java.lang.String toString(NamePool pool)

Represent the expression as a string for diagnostics