net.sf.saxon.expr
Class PositionRange

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

All Implemented Interfaces:

Serializable, SourceLocator, Container, EvaluableItem, SequenceIterable, InstructionInfoProvider

public final class PositionRange
extends Expression

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.Expression

EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD

Constructor Summary

PositionRange(Expression pos)
Create a position "range" for an exact position

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, PrintStream out, Configuration config) 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
Expression	getMaxPosition() Get the ending (max) position of the range.
Expression	getMinPosition() Get the starting (min) position of the range
boolean	hasFocusDependentRange() Test whether the range is focus-dependent.
boolean	isFirstPositionOnly() Test if the first and last position are both constant 1
boolean	isMaxSameAsMin() Test whether the max position is (by definition) the same as the min position
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.
boolean	replaceSubExpression(Expression original, Expression replacement) Replace one subexpression by a replacement subexpression
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.Expression

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

Methods inherited from class java.lang.Object

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

Constructor Detail

PositionRange

public PositionRange(Expression min,
                     Expression max)

Create a position range

PositionRange

public PositionRange(Expression pos)

Create a position "range" for an exact position

PositionRange

public PositionRange(int min,
                     int max)

Create a constant position range

Method Detail

getMinPosition

public Expression getMinPosition()

Get the starting (min) position of the range

getMaxPosition

public Expression getMaxPosition()

Get the ending (max) position of the range. If the range is open-ended, or if the max position is by definition the same as the min, return null

isMaxSameAsMin

public boolean isMaxSameAsMin()

Test whether the max position is (by definition) the same as the min position

simplify

public Expression simplify(StaticContext env)
                    throws XPathException

Simplify an expression

Overrides:

simplify in class Expression

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

Overrides:

typeCheck in class 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:

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

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.

Overrides:

optimize in class Expression

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 Expression

Returns:

StaticProperty.NON_CREATIVE.

evaluateItem

public Item evaluateItem(XPathContext c)
                  throws XPathException

Evaluate the expression

Specified by:

evaluateItem in interface EvaluableItem

Overrides:

evaluateItem in class Expression

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

Specified by:

getItemType in class Expression

Parameters:

th -

Returns:

Type.BOOLEAN

computeCardinality

public int computeCardinality()

Determine the static cardinality

getIntrinsicDependencies

public int getIntrinsicDependencies()

Get the dependencies

Overrides:

getIntrinsicDependencies in class Expression

Returns:

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

iterateSubExpressions

public 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.

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

Specified by:

replaceSubExpression in interface Container

Overrides:

replaceSubExpression in class Expression

Parameters:

original - the original subexpression

replacement - the replacement subexpression

Returns:

true if the original subexpression is found

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,
                    PrintStream out,
                    Configuration config)

Diagnostic print of expression structure

Specified by:

display in class Expression

Parameters:

level - indentation level for this expression

out - Output destination