Package net.sf.saxon.expr
Class PathExpression
- java.lang.Object
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- net.sf.saxon.expr.Expression
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- net.sf.saxon.expr.SlashExpression
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- net.sf.saxon.expr.PathExpression
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- All Implemented Interfaces:
java.io.Serializable
,javax.xml.transform.SourceLocator
,LocationProvider
,SaxonLocator
,ContextMappingFunction
,EvaluableItem
,SequenceIterable
,InstructionInfo
,org.xml.sax.Locator
public final class PathExpression extends SlashExpression 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.This class inherits from SlashExpression; it is used in the common case where the SlashExpression is known to return nodes rather than atomic values.
This class is not responsible for sorting the results into document order or removing duplicates. That is done by a DocumentSorter expression which is wrapped around the path expression. However, this class does contain the logic for deciding statically whether the DocumentSorter is needed or not.
- See Also:
- Serialized Form
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Field Summary
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Fields inherited from class net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, locationId, PROCESS_METHOD, staticProperties
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Constructor Summary
Constructors Constructor Description PathExpression(Expression start, Expression step)
Constructor
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description PathMap.PathMapNodeSet
addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
Add a representation of this expression to a PathMap.int
computeSpecialProperties()
Get the static properties of this expression (other than its type).Expression
copy()
Copy an expression.void
explain(ExpressionPresenter destination)
Diagnostic print of expression structure.Expression
getFirstStep()
Get the first step in this expression.Expression
getLastStep()
Get the last step of the path expressionExpression
getLeadingSteps()
Get a path expression consisting of all steps except the lastExpression
getRemainingSteps()
Get all steps after the first.boolean
isAbsolute(TypeHierarchy th)
Test whether a path expression is an absolute path - that is, a path whose first step selects a document nodeboolean
isHybrid()
Determine whether this expression is capable (as far as static analysis is concerned) of returning a mixture of nodes and atomic values.SequenceIterator
iterate(XPathContext context)
Iterate the path-expression in a given contextExpression
optimize(ExpressionVisitor visitor, ItemType contextItemType)
Optimize the expression and perform type analysisExpression
promote(PromotionOffer offer)
Promote this expression if possibleExpression
simplify(ExpressionVisitor visitor)
Simplify an expressionjava.lang.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.SlashExpression
computeCardinality, computeDependencies, equals, getItemType, getStartExpression, getStepExpression, hashCode, hasLoopingSubexpression, iterateSubExpressions, makeSlashExpression, map, promoteFocusIndependentSubexpressions, replaceSubExpression, setStartExpression, setStepExpression
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Methods inherited from class net.sf.saxon.expr.Expression
adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeStaticProperties, display, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, evaluatePendingUpdates, explain, findParentOf, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, implementsStaticTypeCheck, isUpdatingExpression, iterateEvents, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, typeError
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Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
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Methods inherited from interface net.sf.saxon.expr.ContextMappingFunction
map
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Constructor Detail
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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
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Method Detail
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isHybrid
public boolean isHybrid()
Description copied from class:SlashExpression
Determine whether this expression is capable (as far as static analysis is concerned) of returning a mixture of nodes and atomic values. If so, this needs to be prevented at run time- Overrides:
isHybrid
in classSlashExpression
- Returns:
- true if the static type allows both nodes and atomic values
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simplify
public Expression simplify(ExpressionVisitor visitor) throws XPathException
Simplify an expression- Overrides:
simplify
in classSlashExpression
- Parameters:
visitor
- the expression visitor- Returns:
- the simplified expression
- Throws:
XPathException
- if an error is discovered during expression rewriting
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typeCheck
public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException
Perform type analysis- Overrides:
typeCheck
in classSlashExpression
- Parameters:
visitor
- an expression visitorcontextItemType
- 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 toType.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)
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optimize
public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType) throws XPathException
Optimize the expression and perform type analysis- Overrides:
optimize
in classSlashExpression
- Parameters:
visitor
- an expression visitorcontextItemType
- 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 toType.ITEM_TYPE
- Returns:
- the original expression, rewritten if appropriate to optimize execution
- Throws:
XPathException
- if an error is discovered during this phase (typically a type error)
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promote
public Expression promote(PromotionOffer offer) throws XPathException
Promote this expression if possible- Overrides:
promote
in classSlashExpression
- 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
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copy
public Expression copy()
Copy an expression. This makes a deep copy.- Overrides:
copy
in classSlashExpression
- Returns:
- the copy of the original expression
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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 classSlashExpression
- Returns:
- the special properties, as a bit-significant integer
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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
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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
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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
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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
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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
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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.
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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 classExpression
- Parameters:
pathMap
- the PathMap to which the expression should be addedpathMapNodeSet
-- 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
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iterate
public SequenceIterator iterate(XPathContext context) throws XPathException
Iterate the path-expression in a given context- Specified by:
iterate
in interfaceSequenceIterable
- Overrides:
iterate
in classSlashExpression
- 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
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toString
public java.lang.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 classExpression
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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 classSlashExpression
- Parameters:
destination
- the expression presenter used to display the structure
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