net.sf.saxon.instruct
Class Instruction

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

All Implemented Interfaces:

Serializable, SourceLocator, Container, EvaluableItem, SequenceIterable, TailCallReturner, InstructionInfoProvider

Direct Known Subclasses:

AnalyzeString, ApplyImports, ApplyTemplates, Block, CallTemplate, Choose, CopyOf, Doctype, ForEach, ForEachGroup, GeneralVariable, Message, ParentNodeConstructor, ResultDocument, SimpleNodeConstructor, TraceWrapper, UseAttributeSets, While

public abstract class Instruction
extends Expression
implements SourceLocator, TailCallReturner

Abstract superclass for all instructions in the compiled stylesheet. This represents a compiled instruction, and as such, the minimum information is retained from the original stylesheet.
Note: this class implements SourceLocator: that is, it can identify where in the stylesheet the source instruction was located.

See Also:

Serialized Form

Field Summary

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

Instruction()
Constructor

Method Summary

static void	appendItem(Item it, SequenceReceiver out, int locationId) Static method to append an item that results from evaluating an expression to the current result receiver.
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.
String	evaluateAsString(XPathContext context) Evaluate an expression as a String.
Item	evaluateItem(XPathContext context) Evaluate an expression as a single item.
int	getImplementationMethod() An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
InstructionInfo	getInstructionInfo() Get InstructionInfo for this expression
int	getInstructionNameCode() Get the namecode of the instruction for use in diagnostics
ItemType	getItemType(TypeHierarchy th) Get the item type of the items returned by evaluating this instruction
SourceLocator	getSourceLocator() Get a SourceLocator identifying the location of this instruction
boolean	isXSLT() Establish whether this is an XSLT instruction or an XQuery instruction (used to produce appropriate diagnostics)
SequenceIterator	iterate(XPathContext context) Return an Iterator to iterate over the values of a sequence.
void	process(XPathContext context) Process the instruction, without returning any tail calls
abstract TailCall	processLeavingTail(XPathContext context) ProcessLeavingTail: called to do the real work of this instruction.
Expression	promote(PromotionOffer offer) Offer promotion for this subexpression.
abstract Expression	simplify(StaticContext env) Simplify an expression.

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

adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, display, doPromotion, effectiveBooleanValue, getCardinality, getColumnNumber, getContainingProcedure, getDependencies, getExecutable, getHostLanguage, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, iterateSubExpressions, markTailFunctionCalls, optimize, replaceSubExpression, resetStaticProperties, setLocationId, setParentExpression, setParentExpression, suppressValidation, typeCheck

Methods inherited from class java.lang.Object

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

Methods inherited from interface javax.xml.transform.SourceLocator

getColumnNumber, getLineNumber, getPublicId, getSystemId

Constructor Detail

Instruction

public Instruction()

Constructor

Method Detail

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 prefered. For instructions this is the process() method.

Overrides:

getImplementationMethod in class Expression

getInstructionNameCode

public int getInstructionNameCode()

Get the namecode of the instruction for use in diagnostics

getItemType

public ItemType getItemType(TypeHierarchy th)

Get the item type of the items returned by evaluating this instruction

Specified by:

getItemType in class Expression

Parameters:

th -

Returns:

the static item type of the instruction

computeCardinality

public int computeCardinality()

Get the cardinality of the sequence returned by evaluating this instruction

Returns:

the static cardinality

processLeavingTail

public abstract TailCall processLeavingTail(XPathContext context)
                                     throws XPathException

ProcessLeavingTail: called to do the real work of this instruction. This method must be implemented in each subclass. The results of the instruction are written to the current Receiver, which can be obtained via the Controller.

Specified by:

processLeavingTail in interface TailCallReturner

Parameters:

context - The dynamic context of the transformation, giving access to the current node, the current variables, etc.

Returns:

null if the instruction has completed execution; or a TailCall indicating a function call or template call that is delegated to the caller, to be made after the stack has been unwound so as to save stack space.

Throws:

XPathException

process

public void process(XPathContext context)
             throws XPathException

Process the instruction, without returning any tail calls

Overrides:

process in class Expression

Parameters:

context - The dynamic context, giving access to the current node, the current variables, etc.

Throws:

XPathException

getSourceLocator

public SourceLocator getSourceLocator()

Get a SourceLocator identifying the location of this instruction

simplify

public abstract Expression simplify(StaticContext env)
                             throws XPathException

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

Overrides:

simplify in class Expression

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 Expression

Returns:

a set of flags indicating static properties of this expression

createsNewNodes

public boolean createsNewNodes()

Determine whether this instruction creates new nodes. This implementation returns a default value of false

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. This method is always called at compile time.

Overrides:

promote in class 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

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException

Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.

Specified by:

evaluateItem in interface EvaluableItem

Overrides:

evaluateItem in class Expression

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

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 class 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

evaluateAsString

public final String evaluateAsString(XPathContext context)
                              throws XPathException

Evaluate an expression as a String. This function must only be called in contexts where it is known that the expression will return a single string (or where an empty sequence is to be treated as a zero-length string). Implementations should not attempt to convert the result to a string, other than converting () to "". This method is used mainly to evaluate expressions produced by compiling an attribute value template.

Overrides:

evaluateAsString in class Expression

Parameters:

context - The context in which the expression is to be evaluated

Returns:

the value of the expression, evaluated in the current context. The expression must return a string or (); if the value of the expression is (), this method returns "".

Throws:

XPathException - if any dynamic error occurs evaluating the expression

ClassCastException - if the result type of the expression is not xs:string?

getInstructionInfo

public InstructionInfo getInstructionInfo()

Description copied from class: Expression

Get InstructionInfo for this expression

Specified by:

getInstructionInfo in interface InstructionInfoProvider

Overrides:

getInstructionInfo in class Expression

appendItem

public static void appendItem(Item it,
                              SequenceReceiver out,
                              int locationId)
                       throws XPathException

Static method to append an item that results from evaluating an expression to the current result receiver. The method checks to see whether the item returned from the expression is actually a function-call-package representing the result of a tail call optimization; if so, the tail function calls are complete and the final result is passed on.

Parameters:

it - the item: possibly a FunctionCallPackage

out - the Receiver

Throws:

XPathException

isXSLT

public boolean isXSLT()

Establish whether this is an XSLT instruction or an XQuery instruction (used to produce appropriate diagnostics)

Returns:

true for XSLT, false for XQuery