Package net.sf.saxon.expr
Class SingletonAtomizer
- java.lang.Object
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- net.sf.saxon.expr.ComputedExpression
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- net.sf.saxon.expr.UnaryExpression
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- net.sf.saxon.expr.SingletonAtomizer
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- All Implemented Interfaces:
java.io.Serializable
,javax.xml.transform.SourceLocator
,Container
,Expression
,InstructionInfoProvider
public final class SingletonAtomizer extends UnaryExpression
A SingletonAtomizer combines the functions of an Atomizer and a CardinalityChecker: it is used to atomize a sequence of nodes, checking that the result of the atomization contains zero or one atomic values. Note that the input may be a sequence of nodes or atomic values, even though the result must contain at most one atomic value.- See Also:
- Serialized Form
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Field Summary
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Fields inherited from class net.sf.saxon.expr.UnaryExpression
operand
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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 SingletonAtomizer(Expression sequence, RoleLocator role, boolean allowEmpty)
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
computeSpecialProperties()
Determine the special properties of this expressionprotected java.lang.String
displayOperator(Configuration config)
Give a string representation of the operator for use in diagnosticsItem
evaluateItem(XPathContext context)
Evaluate as an Item.ItemType
getItemType(TypeHierarchy th)
Determine the data type of the items returned by the expression, if possibleRoleLocator
getRole()
Get the RoleLocator (used to construct error messages)Expression
simplify(StaticContext env)
Simplify an expressionExpression
typeCheck(StaticContext env, ItemType contextItemType)
Type-check the expression-
Methods inherited from class net.sf.saxon.expr.UnaryExpression
display, equals, getBaseExpression, hashCode, iterateSubExpressions, optimize, promote, replaceSubExpression
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Methods inherited from class net.sf.saxon.expr.ComputedExpression
adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, iterate, markTailFunctionCalls, process, resetStaticProperties, setLocationId, setParentExpression, setParentExpression, suppressValidation, typeError
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Constructor Detail
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SingletonAtomizer
public SingletonAtomizer(Expression sequence, RoleLocator role, boolean allowEmpty)
Constructor- Parameters:
sequence
- the sequence to be atomizedallowEmpty
- true if the result sequence is allowed to be empty.
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Method Detail
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simplify
public Expression simplify(StaticContext env) throws XPathException
Simplify an expression- Specified by:
simplify
in interfaceExpression
- Overrides:
simplify
in classUnaryExpression
- 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
Type-check the expression- Specified by:
typeCheck
in interfaceExpression
- Overrides:
typeCheck
in classUnaryExpression
- 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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computeSpecialProperties
public int computeSpecialProperties()
Determine the special properties of this expression- Overrides:
computeSpecialProperties
in classUnaryExpression
- Returns:
StaticProperty.NON_CREATIVE
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getRole
public RoleLocator getRole()
Get the RoleLocator (used to construct error messages)
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evaluateItem
public Item evaluateItem(XPathContext context) throws XPathException
Evaluate as an Item. This should only be called if the Atomizer has cardinality zero-or-one, which will only be the case if the underlying expression has cardinality zero-or-one.- Specified by:
evaluateItem
in interfaceExpression
- Overrides:
evaluateItem
in classComputedExpression
- Parameters:
context
- The context in which the expression is to be evaluated- Returns:
- the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence
- Throws:
XPathException
- if any dynamic error occurs evaluating the expression
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getItemType
public ItemType getItemType(TypeHierarchy th)
Determine the data type of the items returned by the expression, if possible- Specified by:
getItemType
in interfaceExpression
- Overrides:
getItemType
in classUnaryExpression
- Parameters:
th
-- Returns:
- a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER. For this class, the result is always an atomic type, but it might be more specific.
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computeCardinality
public int computeCardinality()
Determine the static cardinality of the expression- Overrides:
computeCardinality
in classUnaryExpression
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displayOperator
protected java.lang.String displayOperator(Configuration config)
Give a string representation of the operator for use in diagnostics- Specified by:
displayOperator
in classUnaryExpression
- Parameters:
config
-- Returns:
- the operator, as a string
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