net.sf.saxon.expr
Class FilterExpression

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

All Implemented Interfaces:

Serializable, Expression

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

lineNumber, NO_ARGUMENTS, staticProperties

Constructor Summary

FilterExpression(Expression start, Expression filter)
Constructor

Method Summary

Expression	analyze(StaticContext env) Type-check the expression
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) Diagnostic print of expression structure
boolean	equals(Object other) Is this expression the same as another expression?
Expression	getBaseExpression() Get the underlying expression
Expression	getFilter() Get the filter expression
ItemType	getItemType() Get the data type of the items returned
Expression[]	getSubExpressions() Get the immediate subexpressions of this expression
int	hashCode() get HashCode for comparing two expressions
boolean	isPositional() Determine if the filter is positional
SequenceIterator	iterate(XPathContext context) Iterate over the results, returning them in the correct order
Expression	promote(PromotionOffer offer) Promote this expression if possible
Expression	simplify() Simplify an expression

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

computeStaticProperties, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, getCardinality, getDependencies, getIntrinsicDependencies, getLineNumber, getSpecialProperties, markTailFunctionCalls, setLineNumber, 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)
                 throws XPathException

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

Throws:

XPathException

Method Detail

getItemType

public ItemType getItemType()

Get the data type of the items returned

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()

Determine if the filter is positional

Returns:

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

simplify

public Expression simplify()
                    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

analyze

public Expression analyze(StaticContext env)
                   throws XPathException

Type-check the expression

Parameters:

env - the static context

Returns:

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

Throws:

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

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

getSubExpressions

public Expression[] getSubExpressions()

Get the immediate subexpressions of this expression

Specified by:

getSubExpressions in interface Expression

Overrides:

getSubExpressions 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(Object other)

Is this expression the same as another expression?

Overrides:

equals in class Object

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

Overrides:

hashCode in class Object

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)

Diagnostic print of expression structure

Parameters:

level - the indentation level