net.sf.saxon.functions
Class Aggregate

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

All Implemented Interfaces:

Serializable, SourceLocator, EvaluableItem, SequenceIterable, InstructionInfoProvider

public class Aggregate
extends SystemFunction

This class implements the sum(), avg(), count() functions,

See Also:

Serialized Form

Field Summary

static int	AVG
static int	COUNT
static int	SUM

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

Aggregate()

Method Summary

static AtomicValue	average(SequenceIterator iter, XPathContext context, SourceLocator location) Calculate average
void	checkArguments(ExpressionVisitor visitor) Static analysis: prevent sorting of the argument
int	computeCardinality() Determine the cardinality of the function.
static int	count(SequenceIterator iter) Get the number of items in a sequence identified by a SequenceIterator
Item	evaluateItem(XPathContext context) Evaluate the function
ItemType	getItemType(TypeHierarchy th) Determine the item type of the value returned by the function
static boolean	isCountFunction(Expression exp) Determine whether a given expression is a call to the count() function
static AtomicValue	total(SequenceIterator iter, XPathContext context, SourceLocator location) Calculate the total of a sequence.

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

addDocToPathMap, computeSpecialProperties, copy, getDetails, getErrorCodeForTypeErrors, makeSystemFunction, optimize, 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, effectiveBooleanValue, 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

SUM

public static final int SUM

See Also:

Constant Field Values

AVG

public static final int AVG

See Also:

Constant Field Values

COUNT

public static final int COUNT

See Also:

Constant Field Values

Constructor Detail

Aggregate

public Aggregate()

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

getItemType

public ItemType getItemType(TypeHierarchy th)

Determine the item type of the value returned by the function

Overrides:

getItemType in class SystemFunction

Parameters:

th - the type hierarchy cache

Returns:

a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known at compile time)

computeCardinality

public int computeCardinality()

Determine the cardinality of the function.

Overrides:

computeCardinality in class SystemFunction

Returns:

the computed cardinality, as one of the values StaticProperty.ALLOWS_ZERO_OR_ONE, StaticProperty.EXACTLY_ONE, StaticProperty.ALLOWS_ONE_OR_MORE, StaticProperty.ALLOWS_ZERO_OR_MORE

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException

Evaluate the function

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

total

public static AtomicValue total(SequenceIterator iter,
                                XPathContext context,
                                SourceLocator location)
                         throws XPathException

Calculate the total of a sequence.

Parameters:

iter - iterator over the items to be totalled

context - the XPath dynamic context

location - location of the expression in the source for diagnostics

Returns:

the total, according to the rules of the XPath sum() function, but returning null if the sequence is empty. (It's then up to the caller to decide what the correct result is for an empty sequence.

Throws:

XPathException

average

public static AtomicValue average(SequenceIterator iter,
                                  XPathContext context,
                                  SourceLocator location)
                           throws XPathException

Calculate average

Parameters:

iter - iterator over the items to be totalled

context - the XPath dynamic context

location - location of the expression in the source for diagnostics

Returns:

the average of the values

Throws:

XPathException

count

public static int count(SequenceIterator iter)
                 throws XPathException

Get the number of items in a sequence identified by a SequenceIterator

Parameters:

iter - The SequenceIterator. This method moves the current position of the supplied iterator; if this isn't safe, make a copy of the iterator first by calling getAnother(). The supplied iterator must be positioned before the first item (there must have been no call on next()).

Returns:

the number of items in the underlying sequence

Throws:

XPathException - if a failure occurs reading the input sequence

isCountFunction

public static boolean isCountFunction(Expression exp)

Determine whether a given expression is a call to the count() function

Parameters:

exp - an expression to be examined

Returns:

true if the expression is a call to the count() function