net.sf.saxon.expr
Class FilterExpression

java.lang.Object
  extended by net.sf.saxon.expr.Expression
      extended by net.sf.saxon.expr.FilterExpression
All Implemented Interfaces:
Serializable, SourceLocator, EvaluableItem, SequenceIterable, InstructionInfoProvider

public final class FilterExpression
extends Expression

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
static int FILTERED
           
 
Fields inherited from class net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
 
Constructor Summary
FilterExpression(Expression start, Expression filter)
          Constructor
 
Method Summary
 PathMap.PathMapNodeSet addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
          Add a representation of this expression to a PathMap.
 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).
 Expression copy()
          Copy an expression.
 boolean equals(Object other)
          Is this expression the same as another expression?
 void explain(ExpressionPresenter out)
          Diagnostic print of expression structure.
 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 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
 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.
 boolean isPositional(TypeHierarchy th)
          Determine if the filter is positional
 boolean isSimpleBooleanFilter()
          Test if the filter always returns a singleton boolean
 SequenceIterator iterate(XPathContext context)
          Iterate over the results, returning them in the correct order
 Iterator iterateSubExpressions()
          Get the immediate subexpressions of this expression
 Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)
          Perform optimisation of an expression and its subexpressions.
 Expression promote(PromotionOffer offer)
          Promote this expression if possible
 boolean replaceSubExpression(Expression original, Expression replacement)
          Replace one subexpression by a replacement subexpression
 Expression simplify(ExpressionVisitor visitor)
          Simplify an expression
 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.
 Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
          Type-check the expression
 
Methods inherited from class net.sf.saxon.expr.Expression
adoptChildExpression, checkPermittedContents, computeStaticProperties, display, doPromotion, effectiveBooleanValue, evaluateAsString, evaluateItem, explain, findParentOf, getCardinality, getColumnNumber, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, implementsStaticTypeCheck, iterateEvents, markTailFunctionCalls, process, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation
 
Methods inherited from class java.lang.Object
getClass, notify, notifyAll, wait, wait, wait
 

Field Detail

FILTERED

public static final int FILTERED
See Also:
Constant Field Values
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

getItemType

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

Specified by:
getItemType in class Expression
Parameters:
th - the type hierarchy cache
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

isSimpleBooleanFilter

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

Returns:
true if the filter is a simple boolean expression

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

simplify

public Expression simplify(ExpressionVisitor visitor)
                    throws XPathException
Simplify an expression

Overrides:
simplify in class Expression
Parameters:
visitor - the expression visitor
Returns:
the simplified expression
Throws:
XPathException - if any failure occurs

typeCheck

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

Overrides:
typeCheck in class 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)
Throws:
XPathException - if an error is discovered during this phase (typically a type error)

optimize

public Expression optimize(ExpressionVisitor visitor,
                           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:
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 Type.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)

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.

Overrides:
addToPathMap in class Expression
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

promote

public Expression promote(PromotionOffer offer)
                   throws XPathException
Promote this expression if possible

Overrides:
promote in class Expression
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 Iterator iterateSubExpressions()
Get the immediate subexpressions of this expression

Overrides:
iterateSubExpressions in class Expression
Returns:
the subexpressions, as an array

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

Overrides:
hasLoopingSubexpression in class Expression
Parameters:
child - the immediate subexpression
Returns:
true if the child expression is evaluated repeatedly

replaceSubExpression

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

Overrides:
replaceSubExpression in class Expression
Parameters:
original - the original subexpression
replacement - the replacement subexpression
Returns:
true if the original subexpression is found

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

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

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 SequenceIterable
Overrides:
iterate in class Expression
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 Expression
Returns:
the dependencies

copy

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

Specified by:
copy in class Expression
Returns:
the copy of the original expression

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

Overrides:
toString in class Expression

explain

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

Specified by:
explain in class Expression
Parameters:
out - the ExpressionPresenter to be used


Copyright (C) Michael H. Kay. All rights reserved.