net.sf.saxon.pattern

Class GeneralPositionalPattern

java.lang.Object

net.sf.saxon.pattern.Pattern

net.sf.saxon.pattern.GeneralPositionalPattern

All Implemented Interfaces:

Serializable, SourceLocator, Container, PatternFinder

public class GeneralPositionalPattern
extends Pattern

A GeneralPositionalPattern is a pattern of the form A[P] where A is an axis expression using the child axis and P is an expression that depends on the position. When this kind of pattern is used for matching streamed nodes, it relies on the histogram data of preceding siblings maintained as part of a FleetingParentNode This class handles cases where the predicate P is arbitrarily complex. Simple comparisons of position() against an integer value are handled by the class SimplePositionalPattern.

See Also:

Serialized Form

Constructor Summary

Constructors

Constructor and Description
GeneralPositionalPattern(NodeTest base, Expression positionExpr) Create a PositionalChildPattern

Method Summary

Methods

Modifier and Type	Method and Description
int	allocateSlots(SlotManager slotManager, int nextFree) Allocate slots to any variables used within the pattern
Pattern	analyze(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) Type-check the pattern, performing any type-dependent optimizations.
boolean	equals(Object other) Determine whether this pattern is the same as another pattern
int	getDependencies() Get the dependencies of the pattern.
int	getFingerprint() Determine the fingerprint of nodes to which this pattern applies.
ItemType	getItemType() Get an ItemType that all the nodes matching this pattern must satisfy
int	getNodeKind() Determine the types of nodes to which this pattern applies.
NodeTest	getNodeTest() Get the base pattern
Expression	getPositionExpr() Get the filter assocated with the pattern
int	hashCode() hashcode supporting equals()
boolean	isMotionless(boolean allowExtensions) Test whether a pattern is motionless, that is, whether it can be evaluated against a node without repositioning the input stream.
Iterator<Expression>	iterateSubExpressions() Iterate over the subexpressions within this pattern
boolean	matches(Item item, XPathContext context) Determine whether the pattern matches a given item.
boolean	matchesBeneathAnchor(NodeInfo node, NodeInfo anchor, XPathContext context) Determine whether this pattern matches a given Node within the subtree rooted at a given anchor node.
void	promote(PromotionOffer offer, Expression parent) Offer promotion for subexpressions within this pattern.
boolean	replaceSubExpression(Expression original, Expression replacement) Replace one subexpression by a replacement subexpression
Pattern	simplify(ExpressionVisitor visitor) Simplify the pattern: perform any context-independent optimisations

Methods inherited from class net.sf.saxon.pattern.Pattern

bindCurrent, getColumnNumber, getContainerGranularity, getDefaultPriority, getExecutable, getHostLanguage, getLineNumber, getLocationProvider, getPublicId, getSystemId, make, replaceCurrent, selectNodes, setExecutable, setLineNumber, setOriginalText, setSystemId, toString

Methods inherited from class java.lang.Object

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

Constructor Detail

GeneralPositionalPattern

public GeneralPositionalPattern(NodeTest base,
                        Expression positionExpr)

Create a PositionalChildPattern

Method Detail

getPositionExpr

public Expression getPositionExpr()

Get the filter assocated with the pattern

Returns:

the filter predicate

getNodeTest

public NodeTest getNodeTest()

Get the base pattern

Returns:

the base pattern before filtering

isMotionless

public boolean isMotionless(boolean allowExtensions)

Test whether a pattern is motionless, that is, whether it can be evaluated against a node without repositioning the input stream. This is a necessary condition for patterns used as the match pattern of a streamed template rule.

Overrides:

isMotionless in class Pattern

Parameters:

allowExtensions - true if Saxon streamability extensions are allowed in the analysis

Returns:

true if the pattern is motionless, that is, if it can be evaluated against a streamed node without changing the position in the streamed input file

simplify

public Pattern simplify(ExpressionVisitor visitor)
                 throws XPathException

Simplify the pattern: perform any context-independent optimisations

Overrides:

simplify in class Pattern

Parameters:

visitor - an expression visitor

Returns:

the optimised Pattern

Throws:

XPathException

analyze

public Pattern analyze(ExpressionVisitor visitor,
              ExpressionVisitor.ContextItemType contextItemType)
                throws XPathException

Type-check the pattern, performing any type-dependent optimizations.

Overrides:

analyze in class Pattern

Parameters:

visitor - an expression visitor

contextItemType - the type of the context item at the point where the pattern appears

Returns:

the optimised Pattern

Throws:

XPathException

getDependencies

public int getDependencies()

Get the dependencies of the pattern. The only possible dependency for a pattern is on local variables. This is analyzed in those patterns where local variables may appear.

Overrides:

getDependencies in class Pattern

Returns:

the dependencies, as a bit-significant mask

iterateSubExpressions

public Iterator<Expression> iterateSubExpressions()

Iterate over the subexpressions within this pattern

Overrides:

iterateSubExpressions in class Pattern

Returns:

an iterator over the subexpressions. Default implementation returns an empty sequence

replaceSubExpression

public boolean replaceSubExpression(Expression original,
                           Expression replacement)

Replace one subexpression by a replacement subexpression

Overrides:

replaceSubExpression in class Pattern

Parameters:

original - the original subexpression

replacement - the replacement subexpression

Returns:

true if the original subexpression is found

allocateSlots

public int allocateSlots(SlotManager slotManager,
                int nextFree)

Allocate slots to any variables used within the pattern

Overrides:

allocateSlots in class Pattern

Parameters:

slotManager -

nextFree - the next slot that is free to be allocated @return the next slot that is free to be allocated

Returns:

the next slot that is free to be allocated

promote

public void promote(PromotionOffer offer,
           Expression parent)
             throws XPathException

Offer promotion for subexpressions within this pattern. The offer will be accepted if the subexpression is not dependent on the factors (e.g. the context item) identified in the PromotionOffer. By default the offer is not accepted - this is appropriate in the case of simple expressions such as constant values and variable references where promotion would give no performance advantage. This method is always called at compile time.

Unlike the corresponding method on Expression, this method does not return anything: it can make internal changes to the pattern, but cannot return a different pattern. Only certain kinds of promotion are applicable within a pattern: specifically, promotions affecting local variable references within the pattern.

Overrides:

promote in class Pattern

Parameters:

offer - details of the offer, for example the offer to move expressions that don't depend on the context to an outer level in the containing expression

parent -

Throws:

XPathException - if any error is detected

matches

public boolean matches(Item item,
              XPathContext context)
                throws XPathException

Determine whether the pattern matches a given item.

Specified by:

matches in class Pattern

Parameters:

item - the item to be tested

context - The dynamic context. Only relevant if the pattern uses variables, or contains calls on functions such as document() or key().

Returns:

true if the pattern matches, else false

Throws:

XPathException - if an error occurs while matching the pattern (the caller will usually treat this the same as a false result)

matchesBeneathAnchor

public boolean matchesBeneathAnchor(NodeInfo node,
                           NodeInfo anchor,
                           XPathContext context)
                             throws XPathException

Determine whether this pattern matches a given Node within the subtree rooted at a given anchor node. This method is used when the pattern is used for streaming.

Overrides:

matchesBeneathAnchor in class Pattern

Parameters:

node - The NodeInfo representing the Element or other node to be tested against the Pattern

anchor - The anchor node, which must match any AnchorPattern subpattern

context - The dynamic context. Only relevant if the pattern uses variables, or contains calls on functions such as document() or key().

Returns:

true if the node matches the Pattern, false otherwise

Throws:

XPathException - if an error occurs while matching the pattern (the caller will usually treat this the same as a false result)

getNodeKind

public int getNodeKind()

Determine the types of nodes to which this pattern applies. Used for optimisation. For patterns that match nodes of several types, return Node.NODE

Overrides:

getNodeKind in class Pattern

Returns:

the type of node matched by this pattern. e.g. Node.ELEMENT or Node.TEXT

getFingerprint

public int getFingerprint()

Determine the fingerprint of nodes to which this pattern applies. Used for optimisation.

Overrides:

getFingerprint in class Pattern

Returns:

the fingerprint of nodes matched by this pattern.

getItemType

public ItemType getItemType()

Get an ItemType that all the nodes matching this pattern must satisfy

Specified by:

getItemType in class Pattern

Returns:

an ItemType, as specific as possible, which all the matching items satisfy

equals

public boolean equals(Object other)

Determine whether this pattern is the same as another pattern

Overrides:

equals in class Object

Parameters:

other - the other object

hashCode

public int hashCode()

hashcode supporting equals()

Overrides:

hashCode in class Object