net.sf.saxon.expr
Class PositionRange

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

All Implemented Interfaces:

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

public final class PositionRange

extends ComputedExpression

PositionRange: a boolean expression that tests whether the position() is within a certain range. This expression can occur in any context but it is optimized when it appears as a predicate (see FilterIterator)

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

PositionRange(Expression min, Expression max)
Create a position range

PositionRange(int min, int max)
Create a constant position range

Method Summary

int	computeCardinality() Determine 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
Item	evaluateItem(XPathContext c) Evaluate the expression
int	getIntrinsicDependencies() Get the dependencies
ItemType	getItemType(TypeHierarchy th) Determine the data type of the expression
boolean	hasFocusDependentRange() Test whether the range is focus-dependent.
boolean	isFirstPositionOnly() Test if the first and last position are both constant 1
java.util.Iterator	iterateSubExpressions() Get the immediate sub-expressions of this expression.
SequenceIterator	makePositionIterator(SequenceIterator base, XPathContext c) Make an iterator over a range of a sequence determined by this position range
TailExpression	makeTailExpression(Expression start) If this is an open-ended range with a constant start position, make a TailExpression.
boolean	matchesAtMostOneItem() Test if the position range matches at most one item
Expression	optimize(Optimizer opt, StaticContext env, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.
Expression	simplify(StaticContext env) Simplify an expression
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, iterate, markTailFunctionCalls, process, promote, resetStaticProperties, setLocationId, setParentExpression, suppressValidation, typeError, typeError

Methods inherited from class java.lang.Object

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

Constructor Detail

PositionRange

public PositionRange(Expression min,
                     Expression max)

Create a position range

PositionRange

public PositionRange(int min,
                     int max)

Create a constant position range

Method Detail

simplify

public Expression simplify(StaticContext env)
                    throws XPathException

Simplify an expression

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

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

computeSpecialProperties

public int computeSpecialProperties()

Determine the special properties of this expression

Overrides:

computeSpecialProperties in class ComputedExpression

Returns:

StaticProperty.NON_CREATIVE.

evaluateItem

public Item evaluateItem(XPathContext c)
                  throws XPathException

Evaluate the expression

Specified by:

evaluateItem in interface Expression

Overrides:

evaluateItem in class ComputedExpression

Parameters:

c - 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

makePositionIterator

public SequenceIterator makePositionIterator(SequenceIterator base,
                                             XPathContext c)
                                      throws XPathException

Make an iterator over a range of a sequence determined by this position range

Throws:

XPathException

getItemType

public ItemType getItemType(TypeHierarchy th)

Determine the data type of the expression

Parameters:

th -

Returns:

Type.BOOLEAN

computeCardinality

public int computeCardinality()

Determine the static cardinality

Specified by:

computeCardinality in class ComputedExpression

getIntrinsicDependencies

public int getIntrinsicDependencies()

Get the 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

iterateSubExpressions

public java.util.Iterator 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.

Specified by:

iterateSubExpressions in interface Expression

Overrides:

iterateSubExpressions in class ComputedExpression

Returns:

an iterator containing the sub-expressions of this expression

isFirstPositionOnly

public boolean isFirstPositionOnly()

Test if the first and last position are both constant 1

hasFocusDependentRange

public boolean hasFocusDependentRange()

Test whether the range is focus-dependent. An example of a focus-dependent range is (1 to position()). We could treat last() specially but we don't.

matchesAtMostOneItem

public boolean matchesAtMostOneItem()

Test if the position range matches at most one item

makeTailExpression

public TailExpression makeTailExpression(Expression start)

If this is an open-ended range with a constant start position, make a TailExpression. Otherwise return null

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