net.sf.saxon.expr

Class PathExpression

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

public final class PathExpression
extends Expression
implements ContextMappingFunction

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.

Field Summary

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD, locationId, staticProperties

Constructor Summary

PathExpression(Expression start, Expression step)
Constructor

Method Summary

PathMap.PathMapNodeSet
addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
Add a representation of this expression to a PathMap.
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).
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.
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)
boolean
hasLoopingSubexpression(Expression child)
Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly
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
Iterator
iterateSubExpressions()
Get the immediate subexpressions of this expression
SequenceIterator
map(XPathContext context)
Mapping function, from a node returned by the start iteration, to a sequence returned by the child.
Expression
optimize(ExpressionVisitor visitor, ItemType contextItemType)
Optimize the expression and perform type analysis
Expression
promote(PromotionOffer offer)
Promote this expression if possible
boolean
replaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpression
Expression
simplify(ExpressionVisitor visitor)
Simplify an expression
String
toString()
The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath.
PathExpression
tryToMakeAbsolute(TypeHierarchy th)
Test whether a path expression is an absolute path - that is, a path whose first step selects a document node; if not, see if it can be converted to an absolute path.
Expression
typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Perform type analysis

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

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 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 int computeCardinality()
Determine the static cardinality of the expression
Overrides:
computeCardinality in interface 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 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

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
Returns:
the first step in the expression, after expanding any nested path expressions

getItemType

public final ItemType getItemType(TypeHierarchy th)
Determine the data type of the items returned by this exprssion
Overrides:
getItemType in interface Expression
Parameters:
th - the type hierarchy cache
Returns:
the type of the step

getLastStep

public Expression getLastStep()
Get the last step of the path expression
Returns:
the last step in the expression, after expanding any nested path expressions

getLeadingSteps

public Expression getLeadingSteps()
Get a path expression consisting of all steps except the last
Returns:
a path expression containing all steps in this path expression other than the last, after expanding any nested path expressions

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
Returns:
a path expression containing all steps in this path expression other than the first, after expanding any nested path expressions

getStartExpression

public Expression getStartExpression()
Get the start expression (the left-hand operand)
Returns:
the left-hand operand

getStepExpression

public Expression getStepExpression()
Get the step expression (the right-hand operand)
Returns:
the right-hand operand

hasLoopingSubexpression

public boolean hasLoopingSubexpression(Expression child)
Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly
Overrides:
hasLoopingSubexpression in interface Expression
Parameters:
child - the immediate subexpression
Returns:
true if the child expression is evaluated repeatedly

hashCode

public int hashCode()
get HashCode for comparing two expressions

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
Parameters:
th - the type hierarchy cache
Returns:
true if the first step in this path expression 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 SequenceIterable
Overrides:
iterate in interface Expression
Parameters:
context - the evaluation context

iterateSubExpressions

public Iterator iterateSubExpressions()
Get the immediate subexpressions of this expression
Overrides:
iterateSubExpressions in interface Expression

map

public SequenceIterator map(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 ContextMappingFunction

optimize

public Expression optimize(ExpressionVisitor visitor,
                           ItemType contextItemType)
            throws XPathException
Optimize the expression and perform type analysis
Overrides:
optimize in interface Expression

promote

public Expression promote(PromotionOffer offer)
            throws XPathException
Promote this expression if possible
Overrides:
promote in interface Expression

replaceSubExpression

public boolean replaceSubExpression(Expression original,
                                    Expression replacement)
Replace one subexpression by a replacement subexpression
Overrides:
replaceSubExpression in interface Expression
Parameters:
original - the original subexpression
replacement - the replacement subexpression
Returns:
true if the original subexpression is found

simplify

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

toString

public String toString()
The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax
Overrides:
toString in interface Expression

tryToMakeAbsolute

public PathExpression tryToMakeAbsolute(TypeHierarchy th)
Test whether a path expression is an absolute path - that is, a path whose first step selects a document node; if not, see if it can be converted to an absolute path. This is possible in cases where the path expression has the form a/b/c and it is known that the context item is a document node; in this case it is safe to change the path expression to /a/b/c
Parameters:
th - the type hierarchy cache
Returns:
the path expression if it is absolute; the converted path expression if it can be made absolute; or null if neither condition applies.

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType contextItemType)
            throws XPathException
Perform type analysis
Overrides:
typeCheck in interface Expression