net.sf.saxon.expr

Class SingleNodeExpression

Implemented Interfaces:
EvaluableItem, InstructionInfoProvider, SequenceIterable, Serializable, SourceLocator
Known Direct Subclasses:
ParentNodeExpression, RootExpression

public abstract class SingleNodeExpression
extends Expression

A node set expression that will always return zero or one nodes

Field Summary

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD, locationId, staticProperties

Method Summary

int
computeCardinality()
Specify that the expression returns a singleton
int
computeSpecialProperties()
Compute the special properties of this expression.
boolean
effectiveBooleanValue(XPathContext context)
Get the effective boolean value of the expression.
Item
evaluateItem(XPathContext context)
Evaluate an expression as a single item.
int
getIntrinsicDependencies()
Determine which aspects of the context the expression depends on.
ItemType
getItemType(TypeHierarchy th)
Determine the data type of the items returned by this expression
abstract NodeInfo
getNode(XPathContext context)
Get the single node to which this expression refers.
SequenceIterator
iterate(XPathContext context)
Evaluate the expression in a given context to return an iterator
Expression
optimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
Expression
typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Type-check the expression.

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

addToPathMap, adoptChildExpression, checkPermittedContents, computeCardinality, computeDependencies, computeSpecialProperties, computeStaticProperties, copy, display, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, explain, explain, findParentOf, getCardinality, getColumnNumber, getConstructType, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getItemType, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterate, iterateEvents, iterateSubExpressions, markTailFunctionCalls, optimize, process, promote, replaceSubExpression, resetLocalStaticProperties, setContainer, setFiltered, setFlattened, setLocationId, simplify, staticTypeCheck, suppressValidation, toString, typeCheck, typeError

Method Details

computeCardinality

public int computeCardinality()
Specify that the expression returns a singleton
Overrides:
computeCardinality in interface Expression

computeSpecialProperties

public int computeSpecialProperties()
Compute the special properties of this expression. These properties are denoted by a bit-significant integer, possible values are in class StaticProperty. The "special" properties are properties other than cardinality and dependencies, and most of them relate to properties of node sequences, for example whether the nodes are in document order.
Overrides:
computeSpecialProperties in interface Expression
Returns:
the special properties, as a bit-significant integer

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext context)
            throws XPathException
Get the effective boolean value of the expression. This returns false if the value is the empty sequence, a zero-length string, a number equal to zero, or the boolean false. Otherwise it returns true.
Overrides:
effectiveBooleanValue in interface Expression
Parameters:
context - The context in which the expression is to be evaluated
Returns:
the effective boolean value
Throws:
XPathException - if any dynamic error occurs evaluating the expression

evaluateItem

public Item evaluateItem(XPathContext context)
            throws XPathException
Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.
Specified by:
evaluateItem in interface EvaluableItem
Overrides:
evaluateItem in interface 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

getIntrinsicDependencies

public int getIntrinsicDependencies()
Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such as StaticProperty.VARIABLES and StaticProperty.CURRENT_NODE
Overrides:
getIntrinsicDependencies in interface Expression

getItemType

public ItemType getItemType(TypeHierarchy th)
Determine the data type of the items returned by this expression
Overrides:
getItemType in interface Expression
Parameters:
th - the type hierarchy cache
Returns:
Type.NODE

getNode

public abstract NodeInfo getNode(XPathContext context)
            throws XPathException
Get the single node to which this expression refers. Returns null if the node-set is empty

iterate

public SequenceIterator iterate(XPathContext context)
            throws XPathException
Evaluate the expression in a given context to return an iterator
Specified by:
iterate in interface SequenceIterable
Overrides:
iterate in interface Expression
Parameters:
context - the evaluation context

optimize

public Expression optimize(ExpressionVisitor visitor,
                           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.

Overrides:
optimize in interface Expression
Parameters:
visitor - an expression visitor
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 if appropriate to optimize execution
Throws:
XPathException - if an error is discovered during this phase (typically a type error)

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType contextItemType)
            throws XPathException
Type-check the expression.
Overrides:
typeCheck in interface Expression