net.sf.saxon.expr

Class FilterExpression

public final class FilterExpression extends Expression implements ContextSwitchingExpression

A FilterExpression contains a base expression and a filter predicate, which may be an integer expression (positional filter), or a boolean expression (qualifier)
Field Summary
static intFILTERED
Constructor Summary
FilterExpression(Expression start, Expression filter)
Constructor
Method Summary
PathMap.PathMapNodeSetaddToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
Add a representation of this expression to a PathMap.
intcomputeCardinality()
Get the static cardinality of this expression
intcomputeDependencies()
Determine which aspects of the context the expression depends on.
intcomputeSpecialProperties()
Get the static properties of this expression (other than its type).
Expressioncopy()
Copy an expression.
booleanequals(Object other)
Is this expression the same as another expression?
voidexplain(ExpressionPresenter out)
Diagnostic print of expression structure.
ExpressiongetControlledExpression()
Get the subexpression that is evaluated in the new context
ExpressiongetControllingExpression()
Get the underlying expression
ExpressiongetFilter()
Get the filter expression
ItemTypegetItemType(TypeHierarchy th)
Get the data type of the items returned
inthashCode()
get HashCode for comparing two expressions
booleanhasLoopingSubexpression(Expression child)
Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly
booleanisIndependentNumericFilter()
Determine whether the filter is a simple independent numeric, that is, an expression that satisfies the following conditions: (a) its value is numeric; (b) the value does not depend on the context item or position; (c) the cardinality is zero or one.
booleanisPositional(TypeHierarchy th)
Determine if the filter is positional
booleanisSimpleBooleanFilter()
Test if the filter always returns a singleton boolean
SequenceIteratoriterate(XPathContext context)
Iterate over the results, returning them in the correct order
Iterator<Expression>iterateSameFocusSubExpressions()
Get the immediate sub-expressions of this expression that are evaluated with the same focus (context item, position, and size) as the parent expression.
Iterator<Expression>iterateSubExpressions()
Get the immediate subexpressions of this expression
Expressionoptimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
Expressionpromote(PromotionOffer offer, Expression parent)
Promote this expression if possible
booleanreplaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpression
Expressionsimplify(ExpressionVisitor visitor)
Simplify an expression
StringtoString()
The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath.
ExpressiontypeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Type-check the expression

Field Detail

FILTERED

public static final int FILTERED

Constructor Detail

FilterExpression

public FilterExpression(Expression start, Expression filter)
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

addToPathMap

public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.

Parameters: pathMap the PathMap to which the expression should be added pathMapNodeSet

Returns: the pathMapNode representing the focus established by this expression, in the case where this expression is the first operand of a path expression or filter expression

computeCardinality

public int computeCardinality()
Get the static cardinality of this expression

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

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

Returns: the dependencies

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.

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

copy

public Expression copy()
Copy an expression. This makes a deep copy.

Returns: the copy of the original expression

equals

public boolean equals(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

explain

public void explain(ExpressionPresenter out)
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Parameters: out the ExpressionPresenter to be used

getControlledExpression

public Expression getControlledExpression()
Get the subexpression that is evaluated in the new context

Returns: the subexpression evaluated in the context set by the controlling expression

getControllingExpression

public Expression getControllingExpression()
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

getItemType

public ItemType getItemType(TypeHierarchy th)
Get the data type of the items returned

Parameters: th the type hierarchy cache

Returns: an integer representing the data type

hashCode

public int hashCode()
get HashCode for comparing two expressions

Returns: the hash code

hasLoopingSubexpression

public boolean hasLoopingSubexpression(Expression child)
Given an expression that is an immediate child of this expression, test whether the evaluation of the parent expression causes the child expression to be evaluated repeatedly

Parameters: child the immediate subexpression

Returns: true if the child expression is evaluated repeatedly

isIndependentNumericFilter

public boolean isIndependentNumericFilter()
Determine whether the filter is a simple independent numeric, that is, an expression that satisfies the following conditions: (a) its value is numeric; (b) the value does not depend on the context item or position; (c) the cardinality is zero or one.

Returns: true if the filter is a numeric value that does not depend on the context item or position

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

isSimpleBooleanFilter

public boolean isSimpleBooleanFilter()
Test if the filter always returns a singleton boolean

Returns: true if the filter is a simple boolean expression

iterate

public SequenceIterator iterate(XPathContext context)
Iterate over the results, returning them in the correct order

Parameters: context the dynamic context for the evaluation

Returns: an iterator over the expression results

Throws: XPathException if any dynamic error occurs

iterateSameFocusSubExpressions

public Iterator<Expression> iterateSameFocusSubExpressions()
Get the immediate sub-expressions of this expression that are evaluated with the same focus (context item, position, and size) as the parent expression.

Returns: an iterator containing those sub-expressions of this expression that are evaluated with the same focus as the parent expression

iterateSubExpressions

public Iterator<Expression> iterateSubExpressions()
Get the immediate subexpressions of this expression

Returns: the subexpressions, as an array

optimize

public Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)
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: visitor an expression visitor 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 ITEM_TYPE

Returns: the original expression, rewritten if appropriate to optimize execution

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

promote

public Expression promote(PromotionOffer offer, Expression parent)
Promote this expression if possible

Parameters: offer details of the promotion that is possible parent

Returns: the promoted expression (or the original expression, unchanged)

replaceSubExpression

public boolean replaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpression

Parameters: original the original subexpression replacement the replacement subexpression

Returns: true if the original subexpression is found

simplify

public Expression simplify(ExpressionVisitor visitor)
Simplify an expression

Parameters: visitor the expression visitor

Returns: the simplified expression

Throws: XPathException if any failure occurs

toString

public String toString()
The toString() method for an expression attempts to give a representation of the expression in an XPath-like form, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax

typeCheck

public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Type-check the expression

Parameters: visitor the expression visitor contextItemType the type of the context item for this expression

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