Package net.sf.saxon.expr
Class FilterExpression
java.lang.Object
net.sf.saxon.expr.ComputedExpression
net.sf.saxon.expr.FilterExpression
- All Implemented Interfaces:
Serializable
,SourceLocator
,Container
,Expression
,InstructionInfoProvider
A FilterExpression contains a base expression and a filter predicate, which may be an
integer expression (positional filter), or a boolean expression (qualifier)
- 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
Get the static cardinality of this 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 underlying expressionGet the filter expressionGet the data type of the items returnedint
hashCode()
get HashCode for comparing two expressionsboolean
Test whether the filter is amenable to indexingboolean
Determine if the filter is positionaliterate
(XPathContext context) Iterate over the results, returning them in the correct orderGet the immediate subexpressions of this expressionoptimize
(Optimizer opt, StaticContext env, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.promote
(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) Type-check the expressionMethods 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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FilterExpression
Constructor- Parameters:
start
- A node-set expression denoting the absolute or relative set of nodes from which the navigation path should start.filter
- An expression defining the filter predicate
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Method Details
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getItemType
Get the data type of the items returned- Parameters:
th
-- Returns:
- an integer representing the data type
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getBaseExpression
Get the underlying expression- Returns:
- the expression being filtered
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getFilter
Get the filter expression- Returns:
- the expression acting as the filter predicate
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isPositional
Determine if the filter is positional- Parameters:
th
- the Type Hierarchy (for cached access to type information)- Returns:
- true if the value of the filter depends on the position of the item against which it is evaluated
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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 any failure occurs
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typeCheck
Type-check the expression- Parameters:
env
- the static contextcontextItemType
- 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 expression after type-checking (potentially modified to add run-time checks and/or conversions)
- Throws:
XPathException
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optimize
public Expression optimize(Optimizer opt, StaticContext env, ItemType contextItemType) throws XPathException Perform optimisation of an expression and its subexpressions.This method is called after all references to functions and variables have been resolved to the declaration of the function or variable, and after all type checking has been done.
- 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
Promote this expression if possible- Specified by:
promote
in interfaceExpression
- Overrides:
promote
in classComputedExpression
- Parameters:
offer
- details of the promotion that is possible- Returns:
- the promoted expression (or the original expression, unchanged)
- 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:
- the subexpressions, as an array
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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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computeCardinality
public int computeCardinality()Get the static cardinality of this expression- Specified by:
computeCardinality
in classComputedExpression
- Returns:
- the cardinality. The method attempts to determine the case where the filter predicate is guaranteed to select at most one item from the sequence being filtered
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computeSpecialProperties
public int computeSpecialProperties()Get the static properties of this expression (other than its type). The result is bit-significant. 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
- Returns:
- the static properties of the expression, as a bit-significant value
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equals
Is this expression the same as another expression? -
hashCode
public int hashCode()get HashCode for comparing two expressions -
iterate
Iterate over the results, returning them in the correct order- Specified by:
iterate
in interfaceExpression
- Overrides:
iterate
in classComputedExpression
- Parameters:
context
- the dynamic context for the evaluation- Returns:
- an iterator over the expression results
- Throws:
XPathException
- if any dynamic error occurs
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isIndexable
public boolean isIndexable()Test whether the filter is amenable to indexing -
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 dependencies
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display
Diagnostic print of expression structure- Parameters:
level
- the indentation levelout
-config
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