Package net.sf.saxon.expr
Class PathExpression
- java.lang.Object
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- net.sf.saxon.expr.ComputedExpression
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- net.sf.saxon.expr.PathExpression
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- All Implemented Interfaces:
java.io.Serializable
,javax.xml.transform.SourceLocator
,Container
,ContextMappingFunction
,Expression
,InstructionInfoProvider
public final class PathExpression extends ComputedExpression 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.- See Also:
- Serialized Form
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Field Summary
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Fields inherited from class net.sf.saxon.expr.ComputedExpression
locationId, staticProperties
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Fields inherited from interface net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
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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 int
computeCardinality()
Determine the static cardinality of the expressionint
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, java.io.PrintStream out, Configuration config)
Diagnostic print of expression structureboolean
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 exprssionExpression
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.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 expressionsboolean
isAbsolute(TypeHierarchy th)
Test whether a path expression is an absolute path - that is, a path whose first step selects a document nodeSequenceIterator
iterate(XPathContext context)
Iterate the path-expression in a given contextjava.util.Iterator
iterateSubExpressions()
Get the immediate subexpressions of this expressionSequenceIterator
map(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 analysisExpression
promote(PromotionOffer offer)
Promote this expression if possibleboolean
replaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpressionExpression
simplify(StaticContext env)
Simplify an expressionExpression
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, 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 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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getStartExpression
public Expression getStartExpression()
Get the start expression (the left-hand operand)
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getStepExpression
public Expression getStepExpression()
Get the step expression (the right-hand operand)
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getItemType
public final ItemType getItemType(TypeHierarchy th)
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
public Expression simplify(StaticContext env) throws XPathException
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
public Expression typeCheck(StaticContext env, ItemType contextItemType) throws XPathException
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:
StaticError
- if an error is discovered during this phase (typically a type error)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:
StaticError
- if an error is discovered during this phase (typically a type error)XPathException
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promote
public Expression promote(PromotionOffer offer) throws XPathException
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
public java.util.Iterator 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
public boolean replaceSubExpression(Expression original, Expression replacement)
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
public boolean equals(java.lang.Object other)
Is this expression the same as another expression?- Overrides:
equals
in classjava.lang.Object
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hashCode
public int hashCode()
get HashCode for comparing two expressions- Overrides:
hashCode
in classjava.lang.Object
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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
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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
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getLastStep
public Expression getLastStep()
Get the last step of the path expression
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getLeadingSteps
public Expression getLeadingSteps()
Get a path expression consisting of all steps except the last
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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
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iterate
public SequenceIterator iterate(XPathContext context) throws XPathException
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
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 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
public void display(int level, java.io.PrintStream out, Configuration config)
Diagnostic print of expression structure- Specified by:
display
in interfaceExpression
- Parameters:
level
- indentation level for this expressionout
- Output destination
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