net.sf.saxon.sort
Class TupleSorter

java.lang.Object
  |
  +--net.sf.saxon.expr.ComputedExpression
        |
        +--net.sf.saxon.sort.TupleSorter

All Implemented Interfaces:

Expression, MappingFunction, java.io.Serializable

public class TupleSorter

extends ComputedExpression

implements MappingFunction

A TupleSorter is an expression that sorts a stream of tuples. It is used to implement XQuery FLWR expressions.

See Also:

Serialized Form

Field Summary

 

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

lineNumber, NO_ARGUMENTS, staticProperties

 

Constructor Summary

TupleSorter(Expression base, FixedSortKeyDefinition[] keys)

 

Method Summary
Expression	analyze(StaticContext env)           Perform static analysis of an expression and its subexpressions.
int	computeCardinality()
void	display(int level, NamePool pool)           Diagnostic print of expression structure.
boolean	effectiveBooleanValue(XPathContext context)           Get the effective boolean value of the expression.
ItemType	getItemType()           Determine the data type of the expression, if possible.
Expression[]	getSubExpressions()           Get the immediate sub-expressions of this expression.
SequenceIterator	iterate(XPathContext context)           Return an Iterator to iterate over the values of a sequence.
java.lang.Object	map(Item item, XPathContext context, java.lang.Object info)           Mapping function to map the wrapped objects returned by the SortedTupleIterator into real items.
Expression	promote(PromotionOffer offer)           Promote this expression if possible
Expression	simplify()           Simplify an expression.

 

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

computeDependencies, computeSpecialProperties, computeStaticProperties, dynamicError, evaluateAsString, evaluateItem, getCardinality, getDependencies, getIntrinsicDependencies, getLineNumber, getSourceLocator, getSpecialProperties, markTailFunctionCalls, setLineNumber, typeError

 

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

 

Constructor Detail

TupleSorter

public TupleSorter(Expression base,
                   FixedSortKeyDefinition[] keys)

simplify

public Expression simplify()
                    throws XPathException

Description copied from class: ComputedExpression

Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.

Specified by:

simplify in interface Expression

Overrides:

simplify in class ComputedExpression

Returns:

the simplified expression

Throws:

XPathException - if an error is discovered during expression rewriting

analyze

public Expression analyze(StaticContext env)
                   throws XPathException

Description copied from interface: Expression

Perform static analysis of an expression and its subexpressions.

This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion. A static type error is reported only if execution cannot possibly succeed, that is, if a run-time type error is inevitable. The call may return a modified form of the expression.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable. However, the types of such functions and variables will only be accurately known if they have been explicitly declared.

Specified by:

analyze in interface Expression

Parameters:

env - the static context of the expression

Returns:

the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations

XPathException

getItemType

public ItemType getItemType()

Description copied from interface: Expression

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.

Specified by:

getItemType in interface Expression

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()

Specified by:

computeCardinality in class ComputedExpression

getSubExpressions

public Expression[] getSubExpressions()

Description copied from class: ComputedExpression

Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.

Specified by:

getSubExpressions in interface Expression

Overrides:

getSubExpressions in class ComputedExpression

Returns:

an array containing the sub-expressions of this expression

promote

public Expression promote(PromotionOffer offer)
                   throws XPathException

Promote this expression if possible

Specified by:

promote in interface Expression

Overrides:

promote in class ComputedExpression

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

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException

Description copied from class: ComputedExpression

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 Expression

Overrides:

iterate in class ComputedExpression

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

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext context)
                              throws XPathException

Description copied from class: ComputedExpression

Get the effective boolean value of the expression. This returns false if the value is the empty sequence, a zero-length string, a number equal to zero, or the boolean false. Otherwise it returns true.

Specified by:

effectiveBooleanValue in interface Expression

Overrides:

effectiveBooleanValue in class ComputedExpression

Parameters:

context - 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

display

public void display(int level,
                    NamePool pool)

Description copied from interface: Expression

Diagnostic print of expression structure. The expression is written to the System.err output stream

Specified by:

display in interface Expression

Parameters:

level - indentation level for this expression

map

public java.lang.Object map(Item item,
                            XPathContext context,
                            java.lang.Object info)
                     throws XPathException

Mapping function to map the wrapped objects returned by the SortedTupleIterator into real items. This is done because each tuple may actually represent a sequence of underlying values that share the same sort key.

Specified by:

map in interface MappingFunction

Parameters:

item - The item to be mapped. If context is supplied, this must be the same as context.currentItem().

context - The processing context. This is supplied only for mapping constructs that set the context node, position, and size. Otherwise it is null.

info - Arbitrary information supplied by the creator of the MappingIterator. It must be read-only and immutable for the duration of the iteration.

Returns:

either (a) a SequenceIterator over the sequence of items that the supplied input item maps to, or (b) an Item if it maps to a single item, or (c) null if it maps to an empty sequence.

XPathException