net.sf.saxon.expr
Class ContextItemExpression

java.lang.Object
  net.sf.saxon.expr.ComputedExpression
      net.sf.saxon.expr.ContextItemExpression

All Implemented Interfaces:

Container, Expression, InstructionInfoProvider, java.io.Serializable, javax.xml.transform.SourceLocator

public final class ContextItemExpression

extends ComputedExpression

This class represents the expression "(dot)", which always returns the context item. This may be a AtomicValue or a Node.

See Also:

Serialized Form

Field Summary

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

locationId, staticProperties

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

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

ContextItemExpression()

Method Summary

int	computeCardinality() Get the static cardinality
int	computeSpecialProperties() Determine the special properties of this expression
void	display(int level, NamePool pool, java.io.PrintStream out) Diagnostic print of expression structure
boolean	equals(java.lang.Object other) Is this expression the same as another expression?
Item	evaluateItem(XPathContext context) Evaluate the expression
int	getIntrinsicDependencies() Determine the intrinsic dependencies of an expression, that is, those which are not derived from the dependencies of its subexpressions.
ItemType	getItemType(TypeHierarchy th) Determine the item type
int	hashCode() get HashCode for comparing two expressions
SequenceIterator	iterate(XPathContext context) Iterate over the value of the expression
Expression	optimize(Optimizer opt, StaticContext env, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.
Expression	typeCheck(StaticContext env, ItemType contextItemType) Type-check the expression.

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

adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, dynamicError, effectiveBooleanValue, evaluateAsString, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, iterateSubExpressions, markTailFunctionCalls, process, promote, resetStaticProperties, setLocationId, setParentExpression, simplify, suppressValidation, typeError, typeError

Methods inherited from class java.lang.Object

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

Constructor Detail

ContextItemExpression

public ContextItemExpression()

Method Detail

typeCheck

public Expression typeCheck(StaticContext env,
                            ItemType contextItemType)
                     throws XPathException

Type-check the expression.

Parameters:

env - the static context of the expression

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 to perform necessary run-time type checks, and to perform other type-related optimizations

Throws:

XPathException

optimize

public Expression optimize(Optimizer opt,
                           StaticContext env,
                           ItemType contextItemType)
                    throws XPathException

Perform optimisation of an expression and its subexpressions.

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.

Parameters:

opt - the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances.

env - the static context of the expression

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:

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

XPathException

getItemType

public ItemType getItemType(TypeHierarchy th)

Determine the item type

Parameters:

th -

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()

Get the static cardinality

Specified by:

computeCardinality in class ComputedExpression

computeSpecialProperties

public int computeSpecialProperties()

Determine the special properties of this expression

Overrides:

computeSpecialProperties in class ComputedExpression

Returns:

StaticProperty.NON_CREATIVE

equals

public boolean equals(java.lang.Object other)

Is this expression the same as another expression?

hashCode

public int hashCode()

get HashCode for comparing two expressions

getIntrinsicDependencies

public int getIntrinsicDependencies()

Description copied from class: ComputedExpression

Determine the intrinsic dependencies of an expression, that is, those which are not derived from the dependencies of its subexpressions. For example, position() has an intrinsic dependency on the context position, while (position()+1) does not. The default implementation of the method returns 0, indicating "no dependencies".

Overrides:

getIntrinsicDependencies in class ComputedExpression

Returns:

a set of bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException

Iterate over the value of the expression

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

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException

Evaluate the expression

Specified by:

evaluateItem in interface Expression

Overrides:

evaluateItem in class ComputedExpression

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

display

public void display(int level,
                    NamePool pool,
                    java.io.PrintStream out)

Diagnostic print of expression structure

Parameters:

level - indentation level for this expression

pool - NamePool used to expand any names appearing in the expression

out - Output destination