net.sf.saxon.expr
Class PathExpression

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

All Implemented Interfaces:

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

public final class PathExpression

extends ComputedExpression

implements MappingFunction

An expression that establishes a set of nodes by following relationships between nodes in the document. Specifically, it consists of a start expression which defines a set of nodes, and a Step which defines a relationship to be followed from those nodes to create a new set of nodes.

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

PathExpression(Expression start, Expression step)
Constructor

Method Summary

int	computeCardinality() Determine the static cardinality of the expression
int	computeDependencies() Determine which aspects of the context the expression depends on.
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?
Expression	getFirstStep() Get the first step in this expression.
ItemType	getItemType(TypeHierarchy th) Determine the data type of the items returned by this exprssion
Expression	getLastStep() Get the last step of the path expression
Expression	getLeadingSteps() Get a path expression consisting of all steps except the last
Expression	getRemainingSteps() Get all steps after the first.
Expression	getStartExpression() Get the start expression (the left-hand operand)
Expression	getStepExpression() Get the step expression (the right-hand operand)
int	hashCode() get HashCode for comparing two expressions
boolean	isAbsolute(TypeHierarchy th) Test whether a path expression is an absolute path - that is, a path whose first step selects a document node
SequenceIterator	iterate(XPathContext context) Iterate the path-expression in a given context
java.util.Iterator	iterateSubExpressions() Get the immediate subexpressions of this expression
java.lang.Object	map(Item item, XPathContext context) Mapping function, from a node returned by the start iteration, to a sequence returned by the child.
Expression	optimize(Optimizer opt, StaticContext env, ItemType contextItemType) Optimize the expression and perform type analysis
Expression	promote(PromotionOffer offer) Promote this expression if possible
Expression	simplify(StaticContext env) Simplify an expression
Expression	typeCheck(StaticContext env, ItemType contextItemType) Optimize the expression and perform type analysis

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

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

Methods inherited from class java.lang.Object

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

Constructor Detail

PathExpression

public PathExpression(Expression start,
                      Expression step)

Constructor

Parameters:

start - A node-set expression denoting the absolute or relative set of nodes from which the navigation path should start.

step - The step to be followed from each node in the start expression to yield a new node-set

Method Detail

getStartExpression

public Expression getStartExpression()

Get the start expression (the left-hand operand)

getStepExpression

public Expression getStepExpression()

Get the step expression (the right-hand operand)

getItemType

public final ItemType getItemType(TypeHierarchy th)

Determine the data type of the items returned by this exprssion

Specified by:

getItemType in interface Expression

Parameters:

th -

Returns:

the type of the step

simplify

public Expression simplify(StaticContext env)
                    throws XPathException

Simplify an expression

Specified by:

simplify in interface Expression

Overrides:

simplify in class ComputedExpression

Returns:

the simplified expression

Throws:

XPathException - if an error is discovered during expression rewriting

typeCheck

public Expression typeCheck(StaticContext env,
                            ItemType contextItemType)
                     throws XPathException

Optimize the expression and perform type analysis

Specified by:

typeCheck in interface 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)
                    throws XPathException

Optimize the expression and perform type analysis

Specified by:

optimize in interface Expression

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

Throws:

XPathException

promote

public Expression promote(PromotionOffer offer)
                   throws XPathException

Promote this expression if possible

Specified by:

promote in interface Expression

Overrides:

promote in class ComputedExpression

Parameters:

offer - details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression

Returns:

if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression

Throws:

XPathException - if any error is detected

iterateSubExpressions

public java.util.Iterator iterateSubExpressions()

Get the immediate subexpressions of this expression

Specified by:

iterateSubExpressions in interface Expression

Overrides:

iterateSubExpressions in class ComputedExpression

Returns:

an iterator containing the sub-expressions of this expression

computeDependencies

public int computeDependencies()

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:

computeDependencies in class ComputedExpression

Returns:

the depencies, as a bit-mask

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

computeCardinality

public int computeCardinality()

Determine the static cardinality of the expression

Specified by:

computeCardinality in class ComputedExpression

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

getFirstStep

public Expression getFirstStep()

Get the first step in this expression. A path expression A/B/C is represented as (A/B)/C, but the first step is A

getRemainingSteps

public Expression getRemainingSteps()

Get all steps after the first. This is complicated by the fact that A/B/C is represented as ((A/B)/C; we are required to return B/C

getLastStep

public Expression getLastStep()

Get the last step of the path expression

getLeadingSteps

public Expression getLeadingSteps()

Get a path expression consisting of all steps except the last

isAbsolute

public boolean isAbsolute(TypeHierarchy th)

Test whether a path expression is an absolute path - that is, a path whose first step selects a document node

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException

Iterate the path-expression in a given context

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

map

public java.lang.Object map(Item item,
                            XPathContext context)
                     throws XPathException

Mapping function, from a node returned by the start iteration, to a sequence returned by the child.

Specified by:

map in interface MappingFunction

Parameters:

item - The item to be mapped. If context is supplied, this must be the same as context.currentItem().

context - The processing context. Some mapping functions use this because they require context information. Some mapping functions modify the context by maintaining the context item and position. In other cases, the context may be null.

Returns:

either (a) a SequenceIterator over the sequence of items that the supplied input item maps to, or (b) an Item if it maps to a single item, or (c) null if it maps to an empty sequence.

Throws:

XPathException

display

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

Diagnostic print of expression structure

Specified by:

display in interface Expression

Parameters:

level - indentation level for this expression

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

out - Output destination