net.sf.saxon.sort

Class ConditionalSorter

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

public class ConditionalSorter
extends Expression

An expression that sorts an underlying sequence into document order if some condition is true, or that returns the sequence "as is" (knowing that it doesn't need sorting) if the condition is false.

Field Summary

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD, locationId, staticProperties

Constructor Summary

ConditionalSorter(Expression condition, DocumentSorter sorter)
Create a conditional document sorter

Method Summary

protected int
computeCardinality()
Compute the static cardinality of this expression
Expression
copy()
Copy an expression.
void
explain(ExpressionPresenter out)
Diagnostic print of expression structure.
int
getCardinality()
Determine the static cardinality of the expression.
Expression
getCondition()
Get the condition under which the nodes need to be sorted
DocumentSorter
getDocumentSorter()
Get the document sorter, which sorts the nodes if the condition is true
int
getImplementationMethod()
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
ItemType
getItemType(TypeHierarchy th)
Determine the data type of the expression, if possible.
SequenceIterator
iterate(XPathContext context)
Return an Iterator to iterate over the values of a sequence.
Iterator
iterateSubExpressions()
Get the immediate sub-expressions of this expression.
Expression
promote(PromotionOffer offer)
Offer promotion for this subexpression.
boolean
replaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpression

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

Constructor Details

ConditionalSorter

public ConditionalSorter(Expression condition,
                         DocumentSorter sorter)
Create a conditional document sorter
Parameters:
condition - the conditional expression
sorter - the sorting expression

Method Details

computeCardinality

protected int computeCardinality()
Compute the static cardinality of this expression
Overrides:
computeCardinality in interface Expression

copy

public Expression copy()
Copy an expression. This makes a deep copy.
Overrides:
copy in interface Expression
Returns:
the copy of the original expression

explain

public void explain(ExpressionPresenter out)
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.
Overrides:
explain in interface Expression
Parameters:
out - the expression presenter used to display the structure

getCardinality

public int getCardinality()
Determine the static cardinality of the expression. This establishes how many items there will be in the result of the expression, at compile time (i.e., without actually evaluating the result.
Overrides:
getCardinality in interface Expression
Returns:
one of the values Cardinality.ONE_OR_MORE, Cardinality.ZERO_OR_MORE, Cardinality.EXACTLY_ONE, Cardinality.ZERO_OR_ONE, Cardinality.EMPTY. This default implementation returns ZERO_OR_MORE (which effectively gives no information).

getCondition

public Expression getCondition()
Get the condition under which the nodes need to be sorted
Returns:
the condition (an expression)

getDocumentSorter

public DocumentSorter getDocumentSorter()
Get the document sorter, which sorts the nodes if the condition is true
Returns:
the document sorter

getImplementationMethod

public int getImplementationMethod()
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 interface Expression
Returns:
the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

getItemType

public ItemType getItemType(TypeHierarchy th)
Determine the data type of the expression, if possible. All expression return sequences, in general; this method determines the type of the items within the sequence, assuming that (a) this is known in advance, and (b) it is the same for all items in the sequence.

This method should always return a result, though it may be the best approximation that is available at the time.

Overrides:
getItemType in interface Expression
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)

iterate

public SequenceIterator iterate(XPathContext context)
            throws XPathException
Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.
Specified by:
iterate in interface SequenceIterable
Overrides:
iterate in interface Expression
Parameters:
context - supplies the context for evaluation
Returns:
a SequenceIterator that can be used to iterate over the result of the expression
Throws:
XPathException - if any dynamic error occurs evaluating the expression

iterateSubExpressions

public Iterator iterateSubExpressions()
Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.
Overrides:
iterateSubExpressions in interface Expression
Returns:
an iterator containing the sub-expressions of this expression

promote

public Expression promote(PromotionOffer offer)
            throws XPathException
Offer promotion for this subexpression. The offer will be accepted if the subexpression is not dependent on the factors (e.g. the context item) identified in the PromotionOffer. By default the offer is not accepted - this is appropriate in the case of simple expressions such as constant values and variable references where promotion would give no performance advantage. This method is always called at compile time.
Overrides:
promote in interface Expression
Parameters:
offer - details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression
Returns:
if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression
Throws:
XPathException - if any error is detected

replaceSubExpression

public boolean replaceSubExpression(Expression original,
                                    Expression replacement)
Replace one subexpression by a replacement subexpression
Overrides:
replaceSubExpression in interface Expression
Parameters:
original - the original subexpression
replacement - the replacement subexpression
Returns:
true if the original subexpression is found