net.sf.saxon.functions
Class Existence

java.lang.Object
  net.sf.saxon.expr.Expression
      net.sf.saxon.expr.FunctionCall
          net.sf.saxon.functions.SystemFunction
              net.sf.saxon.functions.Existence

All Implemented Interfaces:

Serializable, SourceLocator, EvaluableItem, Negatable, SequenceIterable, InstructionInfoProvider

public class Existence
extends SystemFunction
implements Negatable

Implement the exists() and empty() functions

See Also:

Serialized Form

Field Summary

static int	EMPTY
static int	EXISTS

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

Existence()

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

addDocToPathMap, computeCardinality, computeSpecialProperties, copy, getDetails, getErrorCodeForTypeErrors, getItemType, makeSystemFunction, setDetails

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

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

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

addToPathMap, adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, display, doPromotion, evaluateAsString, explain, findParentOf, getCardinality, getColumnNumber, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterate, iterateEvents, markTailFunctionCalls, process, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Field Detail

EXISTS

public static final int EXISTS

See Also:

Constant Field Values

EMPTY

public static final int EMPTY

See Also:

Constant Field Values

Constructor Detail

Existence

public Existence()

Method Detail

checkArguments

public void checkArguments(ExpressionVisitor visitor)
                    throws XPathException

Static analysis: prevent sorting of the argument

Overrides:

checkArguments in class SystemFunction

Parameters:

visitor - the expression visitor

Throws:

XPathException

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 class 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)

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

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext c)
                              throws XPathException

Evaluate the function in a boolean context

Overrides:

effectiveBooleanValue in class Expression

Parameters:

c - 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 c)
                  throws XPathException

Evaluate in a general context

Specified by:

evaluateItem in interface EvaluableItem

Overrides:

evaluateItem in class Expression

Parameters:

c - 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