net.sf.saxon.sort

Class ConditionalSorter

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.

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

Method Summary
protected int	computeCardinality() Compute the static cardinality of this expression
protected int	computeSpecialProperties() Compute the special properties 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<Expression>	iterateSubExpressions() Get the immediate sub-expressions of this expression.
Expression	promote(PromotionOffer offer, Expression parent) Offer promotion for this subexpression.
boolean	replaceSubExpression(Expression original, Expression replacement) Replace one subexpression by a replacement subexpression
Expression	typeCheck(ExpressionVisitor visitor, ItemType contextItemType) Perform type checking of an expression and its subexpressions.

Constructor Detail

ConditionalSorter

public ConditionalSorter(Expression condition, DocumentSorter sorter)

Create a conditional document sorter

Parameters: condition the conditional expression sorter the sorting expression

Method Detail

computeCardinality

protected int computeCardinality()

Compute the static cardinality of this expression

Returns: the computed cardinality, as one of the values ALLOWS_ZERO_OR_ONE, EXACTLY_ONE, ALLOWS_ONE_OR_MORE, ALLOWS_ZERO_OR_MORE

computeSpecialProperties

protected int computeSpecialProperties()

Compute the special properties of this expression. These properties are denoted by a bit-significant integer, possible values are in class StaticProperty. The "special" properties are properties other than cardinality and dependencies, and most of them relate to properties of node sequences, for example whether the nodes are in document order.

Returns: the special properties, as a bit-significant integer

copy

public Expression copy()

Copy an expression. This makes a deep copy.

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.

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.

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.

Returns: the implementation method, for example ConditionalSorter or ConditionalSorter or ConditionalSorter

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.

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)

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.

Parameters: context supplies the context for evaluation

Returns: a SequenceIterator that can be used to iterate over the result of the expression

Throws: net.sf.saxon.trans.XPathException if any dynamic error occurs evaluating the expression

iterateSubExpressions

public Iterator<Expression> 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.

Returns: an iterator containing the sub-expressions of this expression

promote

public Expression promote(PromotionOffer offer, Expression parent)

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.

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 parent

Returns: if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression

Throws: net.sf.saxon.trans.XPathException if any error is detected

replaceSubExpression

public boolean replaceSubExpression(Expression original, Expression replacement)

Replace one subexpression by a replacement subexpression

Parameters: original the original subexpression replacement the replacement subexpression

Returns: true if the original subexpression is found

typeCheck

public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)

Perform type checking of an expression and its subexpressions. This is the second phase of static optimization.