net.sf.saxon.expr
Class SingletonAtomizer

java.lang.Object
  net.sf.saxon.expr.Expression
      net.sf.saxon.expr.UnaryExpression
          net.sf.saxon.expr.SingletonAtomizer

All Implemented Interfaces:

Serializable, SourceLocator, Container, EvaluableItem, SequenceIterable, 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

Field Summary

Fields inherited from class net.sf.saxon.expr.Expression

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

SingletonAtomizer(Expression sequence, RoleLocator role, boolean allowEmpty)
Constructor

Method Summary

int	computeCardinality() Determine the static cardinality of the expression
int	computeSpecialProperties() Determine the special properties of this expression
Item	evaluateItem(XPathContext context) Evaluate as an Item.
ItemType	getItemType(TypeHierarchy th) Determine the data type of the items returned by the expression, if possible
RoleLocator	getRole() Get the RoleLocator (used to construct error messages)
Expression	simplify(StaticContext env) Simplify an expression
Expression	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

Methods inherited from class net.sf.saxon.expr.Expression

adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, effectiveBooleanValue, evaluateAsString, getCardinality, getColumnNumber, getContainingProcedure, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, iterate, markTailFunctionCalls, process, resetStaticProperties, setLocationId, setParentExpression, setParentExpression, suppressValidation

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

SingletonAtomizer

public SingletonAtomizer(Expression sequence,
                         RoleLocator role,
                         boolean allowEmpty)

Constructor

Parameters:

sequence - the sequence to be atomized

allowEmpty - true if the result sequence is allowed to be empty.

Method Detail

simplify

public Expression simplify(StaticContext env)
                    throws XPathException

Simplify an expression

Overrides:

simplify in class UnaryExpression

Returns:

the simplified expression

Throws:

XPathException - if an error is discovered during expression rewriting

typeCheck

public Expression typeCheck(StaticContext env,
                            ItemType contextItemType)
                     throws XPathException

Type-check the expression

Overrides:

typeCheck in class UnaryExpression

Parameters:

env - the static context of the expression

contextItemType - 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 to Type.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

computeSpecialProperties

public int computeSpecialProperties()

Determine the special properties of this expression

Overrides:

computeSpecialProperties in class UnaryExpression

Returns:

StaticProperty.NON_CREATIVE.

getRole

public RoleLocator getRole()

Get the RoleLocator (used to construct error messages)

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException

Evaluate as an Item. This should only be called if a singleton or empty sequence is required; it throws a type error if the underlying sequence is multi-valued.

Specified by:

evaluateItem in interface EvaluableItem

Overrides:

evaluateItem in class Expression

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

getItemType

public ItemType getItemType(TypeHierarchy th)

Determine the data type of the items returned by the expression, if possible

Overrides:

getItemType in class UnaryExpression

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.

computeCardinality

public int computeCardinality()

Determine the static cardinality of the expression

Overrides:

computeCardinality in class UnaryExpression