net.sf.saxon.functions
Class Empty

java.lang.Object
  extended by net.sf.saxon.expr.Expression
      extended by net.sf.saxon.expr.FunctionCall
          extended by net.sf.saxon.functions.SystemFunction
              extended by net.sf.saxon.functions.Aggregate
                  extended by net.sf.saxon.functions.Empty
All Implemented Interfaces:
Serializable, SourceLocator, LocationProvider, SaxonLocator, InstructionInfo, Locator

public class Empty
extends Aggregate

Implementation of the fn:exists function

See Also:
Serialized Form

Field Summary
 
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
EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, PUSH_SELECTION, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, WATCH_METHOD
 
Constructor Summary
Empty()
           
 
Method Summary
 boolean effectiveBooleanValue(XPathContext c)
          Evaluate the function in a boolean context
 Item evaluateItem(XPathContext context)
          Evaluate the function
 int getImplementationMethod()
          An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
 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, ExpressionVisitor.ContextItemType contextItemType)
          Perform optimisation of an expression and its subexpressions.
 
Methods inherited from class net.sf.saxon.functions.Aggregate
checkArguments
 
Methods inherited from class net.sf.saxon.functions.SystemFunction
addContextDocumentArgument, addDocToPathMap, computeCardinality, computeSpecialProperties, copy, equals, getDetails, getErrorCodeForTypeErrors, getItemType, getOperation, getRequiredType, makeSystemFunction, setDetails, useContextItemAsDefault
 
Methods inherited from class net.sf.saxon.expr.FunctionCall
addExternalFunctionCallToPathMap, checkArgumentCount, explain, getArguments, getDisplayName, getExpressionName, getFunctionName, getNumberOfArguments, hashCode, iterateSubExpressions, preEvaluate, promote, replaceSubExpression, setArguments, setFunctionName, simplify, simplifyArguments, toString, typeCheck
 
Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getEvaluationMethod, getExecutable, getHostLanguage, getIntegerBounds, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, hasVariableBinding, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterate, iterateEvents, iterateSameFocusSubExpressions, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, typeError
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
 

Constructor Detail

Empty

public Empty()
Method Detail

getImplementationMethod

public int getImplementationMethod()
Description copied from class: SystemFunction
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided directly. The other methods will always be available indirectly, using an implementation that relies on one of the other methods.

Overrides:
getImplementationMethod in class SystemFunction
Returns:
the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

isNegatable

public boolean isNegatable(ExpressionVisitor visitor)
Check whether this specific instance of the expression is negatable

Returns:
true if it is

negate

public Expression negate()
Return the negation of the expression

Returns:
the negation of the expression

optimize

public Expression optimize(ExpressionVisitor visitor,
                           ExpressionVisitor.ContextItemType 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)

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException
Evaluate the function

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

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


Copyright (c) 2004-2011 Saxonica Limited. All rights reserved.