Package net.sf.saxon.expr
Class PathExpression
java.lang.Object
net.sf.saxon.expr.ComputedExpression
net.sf.saxon.expr.PathExpression
- All Implemented Interfaces:
Serializable
,SourceLocator
,Container
,ContextMappingFunction
,Expression
,InstructionInfoProvider
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:
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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
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionint
Determine the static cardinality of the expressionint
Determine which aspects of the context the expression depends on.int
Get the static properties of this expression (other than its type).void
display
(int level, PrintStream out, Configuration config) Diagnostic print of expression structureboolean
Is this expression the same as another expression?Get the first step in this expression.final ItemType
Determine the data type of the items returned by this exprssionGet the last step of the path expressionGet a path expression consisting of all steps except the lastGet all steps after the first.Get the start expression (the left-hand operand)Get the step expression (the right-hand operand)int
hashCode()
get HashCode for comparing two expressionsboolean
Test whether a path expression is an absolute path - that is, a path whose first step selects a document nodeiterate
(XPathContext context) Iterate the path-expression in a given contextGet the immediate subexpressions of this expressionmap
(XPathContext context) Mapping function, from a node returned by the start iteration, to a sequence returned by the child.optimize
(Optimizer opt, StaticContext env, ItemType contextItemType) Optimize the expression and perform type analysispromote
(PromotionOffer offer) Promote this expression if possibleboolean
replaceSubExpression
(Expression original, Expression replacement) Replace one subexpression by a replacement subexpressionsimplify
(StaticContext env) Simplify an expressiontypeCheck
(StaticContext env, ItemType contextItemType) Optimize the expression and perform type analysisMethods inherited from class net.sf.saxon.expr.ComputedExpression
adoptChildExpression, checkPermittedContents, computeStaticProperties, doPromotion, 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, setParentExpression, suppressValidation, typeError
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Constructor Details
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PathExpression
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 Details
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getStartExpression
Get the start expression (the left-hand operand) -
getStepExpression
Get the step expression (the right-hand operand) -
getItemType
Determine the data type of the items returned by this exprssion- Specified by:
getItemType
in interfaceExpression
- Parameters:
th
-- Returns:
- the type of the step
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simplify
Simplify an expression- Specified by:
simplify
in interfaceExpression
- Overrides:
simplify
in classComputedExpression
- Parameters:
env
- the static context- Returns:
- the simplified expression
- Throws:
XPathException
- if an error is discovered during expression rewriting
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typeCheck
Optimize the expression and perform type analysis- Specified by:
typeCheck
in interfaceExpression
- Parameters:
env
- the static context of the expressioncontextItemType
- 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
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optimize
public Expression optimize(Optimizer opt, StaticContext env, ItemType contextItemType) throws XPathException Optimize the expression and perform type analysis- Specified by:
optimize
in interfaceExpression
- 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 expressioncontextItemType
- 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
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promote
Promote this expression if possible- Specified by:
promote
in interfaceExpression
- Overrides:
promote
in classComputedExpression
- 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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iterateSubExpressions
Get the immediate subexpressions of this expression- Specified by:
iterateSubExpressions
in interfaceExpression
- Overrides:
iterateSubExpressions
in classComputedExpression
- Returns:
- an iterator containing the sub-expressions of this expression
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replaceSubExpression
Replace one subexpression by a replacement subexpression- Specified by:
replaceSubExpression
in interfaceContainer
- Overrides:
replaceSubExpression
in classComputedExpression
- Parameters:
original
- the original subexpressionreplacement
- the replacement subexpression- Returns:
- true if the original subexpression is found
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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 classComputedExpression
- Returns:
- the depencies, as a bit-mask
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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 classComputedExpression
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computeCardinality
public int computeCardinality()Determine the static cardinality of the expression- Specified by:
computeCardinality
in classComputedExpression
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equals
Is this expression the same as another expression? -
hashCode
public int hashCode()get HashCode for comparing two expressions -
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
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
Get the last step of the path expression -
getLeadingSteps
Get a path expression consisting of all steps except the last -
isAbsolute
Test whether a path expression is an absolute path - that is, a path whose first step selects a document node -
iterate
Iterate the path-expression in a given context- Specified by:
iterate
in interfaceExpression
- Overrides:
iterate
in classComputedExpression
- 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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map
Mapping function, from a node returned by the start iteration, to a sequence returned by the child.- Specified by:
map
in interfaceContextMappingFunction
- Parameters:
context
- The processing context. The item to be mapped is the context item identified from this context: the values of position() and last() also relate to the set of items being mapped- Returns:
- a SequenceIterator over the sequence of items that the supplied input item maps to
- Throws:
XPathException
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display
Diagnostic print of expression structure- Specified by:
display
in interfaceExpression
- Parameters:
level
- indentation level for this expressionout
- Output destinationconfig
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