net.sf.saxon.functions

Class Existence

Implemented Interfaces:
EvaluableItem, InstructionInfoProvider, Negatable, SequenceIterable, Serializable, SourceLocator

public class Existence
extends SystemFunction
implements Negatable

Implement the exists() and empty() functions *

Field Summary

static int
EMPTY
static int
EXISTS

Fields inherited from class net.sf.saxon.functions.SystemFunction

operation

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

argument

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD, locationId, staticProperties

Method Summary

void
checkArguments(ExpressionVisitor visitor)
Static analysis: prevent sorting of the argument
boolean
effectiveBooleanValue(XPathContext c)
Evaluate the function in a boolean context
Item
evaluateItem(XPathContext c)
Evaluate in a general context
boolean
isNegatable(ExpressionVisitor visitor)
Check whether this specific instance of the expression is negatable
Expression
negate()
Return the negation of the expression
Expression
optimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.

Methods inherited from class net.sf.saxon.functions.SystemFunction

addContextDocumentArgument, addDocToPathMap, checkArguments, computeCardinality, computeSpecialProperties, copy, getDetails, getErrorCodeForTypeErrors, getItemType, getRequiredType, makeSystemFunction, optimize, setDetails, useContextItemAsDefault

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

addExternalFunctionCallToPathMap, checkArgumentCount, checkArguments, equals, explain, getArguments, getDisplayName, getFunctionName, getNumberOfArguments, hashCode, iterateSubExpressions, optimize, preEvaluate, promote, replaceSubExpression, setArguments, setFunctionName, simplify, simplifyArguments, toString, typeCheck

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

Field Details

EMPTY

public static final int EMPTY
Field Value:
1

EXISTS

public static final int EXISTS
Field Value:
0

Method Details

checkArguments

public void checkArguments(ExpressionVisitor visitor)
            throws XPathException
Static analysis: prevent sorting of the argument
Overrides:
checkArguments in interface SystemFunction

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext c)
            throws XPathException
Evaluate the function in a boolean context
Overrides:
effectiveBooleanValue in interface Expression

evaluateItem

public Item evaluateItem(XPathContext c)
            throws XPathException
Evaluate in a general context
Specified by:
evaluateItem in interface EvaluableItem
Overrides:
evaluateItem in interface Expression

isNegatable

public boolean isNegatable(ExpressionVisitor visitor)
Check whether this specific instance of the expression is negatable
Specified by:
isNegatable in interface Negatable
Returns:
true if it is

negate

public Expression negate()
Return the negation of the expression
Specified by:
negate in interface Negatable
Returns:
the negation of the expression

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 SystemFunction
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)