net.sf.saxon.expr
Class FilterExpression

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

All Implemented Interfaces:

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

public final class FilterExpression

extends ComputedExpression

A FilterExpression contains a base expression and a filter predicate, which may be an integer expression (positional filter), or a boolean expression (qualifier)

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

FilterExpression(Expression start, Expression filter, StaticContext env)
Constructor

Method Summary

int	computeCardinality() Get the static cardinality of this expression
int	computeDependencies() Determine which aspects of the context the expression depends on.
int	computeSpecialProperties() Get the static properties of this expression (other than its type).
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?
Expression	getBaseExpression() Get the underlying expression
Expression	getFilter() Get the filter expression
ItemType	getItemType(TypeHierarchy th) Get the data type of the items returned
int	hashCode() get HashCode for comparing two expressions
boolean	isIndexable()
boolean	isPositional(TypeHierarchy th) Determine if the filter is positional
SequenceIterator	iterate(XPathContext context) Iterate over the results, returning them in the correct order
java.util.Iterator	iterateSubExpressions() Get the immediate subexpressions of this expression
Expression	optimize(Optimizer opt, StaticContext env, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.
Expression	promote(PromotionOffer offer) Promote this expression if possible
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, computeStaticProperties, doPromotion, dynamicError, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, markTailFunctionCalls, process, resetStaticProperties, setLocationId, setParentExpression, suppressValidation, typeError, typeError

Methods inherited from class java.lang.Object

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

Constructor Detail

FilterExpression

public FilterExpression(Expression start,
                        Expression filter,
                        StaticContext env)
                 throws StaticError

Constructor

Parameters:

start - A node-set expression denoting the absolute or relative set of nodes from which the navigation path should start.

filter - An expression defining the filter predicate

Method Detail

getItemType

public ItemType getItemType(TypeHierarchy th)

Get the data type of the items returned

Parameters:

th -

Returns:

an integer representing the data type

getBaseExpression

public Expression getBaseExpression()

Get the underlying expression

Returns:

the expression being filtered

getFilter

public Expression getFilter()

Get the filter expression

Returns:

the expression acting as the filter predicate

isPositional

public boolean isPositional(TypeHierarchy th)

Determine if the filter is positional

Parameters:

th - the Type Hierarchy (for cached access to type information)

Returns:

true if the value of the filter depends on the position of the item against which it is evaluated

isIndexable

public boolean isIndexable()

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 any failure occurs

typeCheck

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

Type-check the expression

Parameters:

env - the static context

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 expression after type-checking (potentially modified to add run-time checks and/or conversions)

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

promote

public Expression promote(PromotionOffer offer)
                   throws XPathException

Promote this expression if possible

Specified by:

promote in interface Expression

Overrides:

promote in class ComputedExpression

Parameters:

offer - details of the promotion that is possible

Returns:

the promoted expression (or the original expression, unchanged)

Throws:

XPathException - if any error is detected

iterateSubExpressions

public java.util.Iterator iterateSubExpressions()

Get the immediate subexpressions of this expression

Specified by:

iterateSubExpressions in interface Expression

Overrides:

iterateSubExpressions in class ComputedExpression

Returns:

the subexpressions, as an array

computeCardinality

public int computeCardinality()

Get the static cardinality of this expression

Specified by:

computeCardinality in class ComputedExpression

Returns:

the cardinality. The method attempts to determine the case where the filter predicate is guaranteed to select at most one item from the sequence being filtered

computeSpecialProperties

public int computeSpecialProperties()

Get the static properties of this expression (other than its type). The result is bit-significant. 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 ComputedExpression

Returns:

the static properties of the expression, as a bit-significant value

equals

public boolean equals(java.lang.Object other)

Is this expression the same as another expression?

Parameters:

other - the expression to be compared with this one

Returns:

true if the two expressions are statically equivalent

hashCode

public int hashCode()

get HashCode for comparing two expressions

Returns:

the hash code

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException

Iterate over the results, returning them in the correct order

Specified by:

iterate in interface Expression

Overrides:

iterate in class ComputedExpression

Parameters:

context - the dynamic context for the evaluation

Returns:

an iterator over the expression results

Throws:

XPathException - if any dynamic error occurs

computeDependencies

public int computeDependencies()

Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such as XPathContext.VARIABLES and XPathContext.CURRENT_NODE

Overrides:

computeDependencies in class ComputedExpression

Returns:

the dependencies

display

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

Diagnostic print of expression structure

Parameters:

level - the indentation level

out -

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