Class ConditionalSorter

  extended by net.sf.saxon.expr.Expression
      extended by net.sf.saxon.expr.sort.ConditionalSorter
All Implemented Interfaces:
Serializable, SourceLocator, LocationProvider, SaxonLocator, EvaluableItem, SequenceIterable, InstructionInfo, Locator

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.

See Also:
Serialized Form

Field Summary
Fields inherited from class net.sf.saxon.expr.Expression
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.
Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, evaluatePendingUpdates, explain, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getEvaluationMethod, getExecutable, getExpressionName, getHostLanguage, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterateEvents, iterateSameFocusSubExpressions, markTailFunctionCalls, optimize, process, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, simplify, staticTypeCheck, suppressValidation, toString, typeError
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail


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

condition - the conditional expression
sorter - the sorting expression
Method Detail


public Expression getCondition()
Get the condition under which the nodes need to be sorted

the condition (an expression)


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

the document sorter


public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType contextItemType)
                     throws XPathException
Perform type checking of an expression and its subexpressions. This is the second phase of static optimization.

typeCheck in class Expression
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
the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations
XPathException - if an error is discovered during this phase (typically a type error)


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.

getCardinality in class Expression
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).


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.

computeSpecialProperties in class Expression
the special properties, as a bit-significant integer


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.

getImplementationMethod in class Expression
the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD


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.

iterateSubExpressions in class Expression
an iterator containing the sub-expressions of this expression


public boolean replaceSubExpression(Expression original,
                                    Expression replacement)
Replace one subexpression by a replacement subexpression

replaceSubExpression in class Expression
original - the original subexpression
replacement - the replacement subexpression
true if the original subexpression is found


protected int computeCardinality()
Compute the static cardinality of this expression

Specified by:
computeCardinality in class Expression
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


public Expression copy()
Copy an expression. This makes a deep copy.

Specified by:
copy in class Expression
the copy of the original expression


public void explain(ExpressionPresenter out)
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Specified by:
explain in class Expression
out - the expression presenter used to display the structure


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.

Specified by:
getItemType in class Expression
th - the type hierarchy cache
a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known at compile time)


public Expression promote(PromotionOffer offer,
                          Expression parent)
                   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.

promote in class Expression
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 -
if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression
XPathException - if any error is detected


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
iterate in class Expression
context - supplies the context for evaluation
a SequenceIterator that can be used to iterate over the result of the expression
XPathException - if any dynamic error occurs evaluating the expression

Copyright (c) 2004-2010 Saxonica Limited. All rights reserved.