net.sf.saxon.instruct
Class SimpleNodeConstructor

java.lang.Object
  net.sf.saxon.expr.Expression
      net.sf.saxon.instruct.Instruction
          net.sf.saxon.instruct.SimpleNodeConstructor

All Implemented Interfaces:

Serializable, SourceLocator, EvaluableItem, SequenceIterable, TailCallReturner, InstructionInfoProvider

Direct Known Subclasses:

Comment, ComputedAttribute, FixedAttribute, Namespace, ProcessingInstruction, ValueOf

public abstract class SimpleNodeConstructor
extends Instruction

Common superclass for XSLT instructions whose content template produces a text value: xsl:attribute, xsl:comment, xsl:processing-instruction, xsl:namespace, and xsl:text, and their XQuery equivalents

See Also:

Serialized Form

Field Summary

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

SimpleNodeConstructor()
Default constructor used by subclasses

Method Summary

int	computeCardinality() Get the cardinality of the sequence returned by evaluating this instruction
int	computeSpecialProperties() Get the static properties of this expression (other than its type).
boolean	createsNewNodes() Determine whether this instruction creates new nodes.
Item	evaluateItem(XPathContext context) Evaluate as an expression.
int	evaluateNameCode(XPathContext context) Run-time method to compute the name of the node being constructed.
CharSequence	expandChildren(XPathContext context) Expand the stylesheet elements subordinate to this one, returning the result as a string.
Expression	getSelect() Get the expression that determines the string value of the constructed node
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.
abstract void	localTypeCheck(ExpressionVisitor visitor, ItemType contextItemType) Method to perform type-checking specific to the kind of instruction
Expression	optimize(ExpressionVisitor visitor, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.
boolean	replaceSubExpression(Expression original, Expression replacement) Replace one subexpression by a replacement subexpression
void	setSelect(Expression select, Configuration config) Set the select expression: the value of this expression determines the string-value of the node
Expression	simplify(ExpressionVisitor visitor) Simplify an expression.
Expression	typeCheck(ExpressionVisitor visitor, ItemType contextItemType) The typeCheck() method is called in XQuery, where node constructors are implemented as Expressions.

Methods inherited from class net.sf.saxon.instruct.Instruction

evaluateAsString, getImplementationMethod, getInstructionInfo, getInstructionNameCode, getItemType, getSourceLocator, isXSLT, process, processLeavingTail, promote

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

addToPathMap, adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, copy, display, doPromotion, effectiveBooleanValue, explain, explain, findParentOf, getCardinality, getColumnNumber, getContainer, getDependencies, getExecutable, getHostLanguage, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterateEvents, markTailFunctionCalls, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, toString

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface javax.xml.transform.SourceLocator

getColumnNumber, getLineNumber, getPublicId, getSystemId

Constructor Detail

SimpleNodeConstructor

public SimpleNodeConstructor()

Default constructor used by subclasses

Method Detail

setSelect

public void setSelect(Expression select,
                      Configuration config)
               throws XPathException

Set the select expression: the value of this expression determines the string-value of the node

Parameters:

select - the expression that computes the string value of the node

config - the Saxon configuration (used for example to do early validation of the content of an attribute against the schema-defined type)

Throws:

XPathException

getSelect

public Expression getSelect()

Get the expression that determines the string value of the constructed node

Returns:

the select expression

createsNewNodes

public final boolean createsNewNodes()

Determine whether this instruction creates new nodes. This implementation returns true.

Overrides:

createsNewNodes in class Instruction

Returns:

true if the instruction creates new nodes (or if it can't be proved that it doesn't)

computeCardinality

public int computeCardinality()

Get the cardinality of the sequence returned by evaluating this instruction

Overrides:

computeCardinality in class Instruction

Returns:

the static cardinality

simplify

public Expression simplify(ExpressionVisitor visitor)
                    throws XPathException

Description copied from class: Instruction

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 class Instruction

Parameters:

visitor - an expression visitor

Returns:

the simplified expression

Throws:

XPathException - if an error is discovered during expression rewriting

computeSpecialProperties

public int computeSpecialProperties()

Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.

Overrides:

computeSpecialProperties in class Instruction

Returns:

a set of flags indicating static properties of this expression

localTypeCheck

public abstract void localTypeCheck(ExpressionVisitor visitor,
                                    ItemType contextItemType)
                             throws XPathException

Method to perform type-checking specific to the kind of instruction

Parameters:

visitor - an expression visitor

contextItemType - the static type of the context item

Throws:

XPathException

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType contextItemType)
                     throws XPathException

The typeCheck() method is called in XQuery, where node constructors are implemented as Expressions. In this case the required type for the select expression is a single string.

Overrides:

typeCheck in class Expression

Parameters:

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

Returns:

the rewritten expression

Throws:

XPathException - if any static errors are found in this expression or any of its children

optimize

public Expression optimize(ExpressionVisitor visitor,
                           ItemType contextItemType)
                    throws XPathException

Description copied from class: Expression

Perform optimisation of an expression and its subexpressions. This is the third and final phase of static optimization.

This method is called after all references to functions and variables have been resolved to the declaration of the function or variable, and after all type checking has been done.

Overrides:

optimize in class Expression

Parameters:

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

Returns:

the original expression, rewritten if appropriate to optimize execution

Throws:

XPathException - if an error is discovered during this phase (typically a type error)

iterateSubExpressions

public Iterator iterateSubExpressions()

Description copied from class: Expression

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 class Expression

Returns:

an iterator containing the sub-expressions of this expression

replaceSubExpression

public boolean replaceSubExpression(Expression original,
                                    Expression replacement)

Replace one subexpression by a replacement subexpression

Overrides:

replaceSubExpression in class Expression

Parameters:

original - the original subexpression

replacement - the replacement subexpression

Returns:

true if the original subexpression is found

expandChildren

public CharSequence expandChildren(XPathContext context)
                            throws XPathException

Expand the stylesheet elements subordinate to this one, returning the result as a string. The expansion must not generate any element or attribute nodes.

Parameters:

context - The dynamic context for the transformation

Returns:

the value that will be used as the string value of the constructed node

Throws:

XPathException - if any error occurs

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException

Evaluate as an expression. We rely on the fact that when these instructions are generated by XQuery, there will always be a valueExpression to evaluate the content

Specified by:

evaluateItem in interface EvaluableItem

Overrides:

evaluateItem in class Instruction

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

evaluateNameCode

public int evaluateNameCode(XPathContext context)
                     throws XPathException

Run-time method to compute the name of the node being constructed. This is overridden for nodes that have a name. The default implementation returns -1, which is suitable for unnamed nodes such as comments

Parameters:

context - the XPath dynamic evaluation context

Returns:

the name pool nameCode identifying the name of the constructed node

Throws:

XPathException - if any failure occurs

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException

Description copied from class: Instruction

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 class Instruction

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