net.sf.saxon.pattern

Class AnchorPattern

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.PseudoExpression

net.sf.saxon.pattern.Pattern

net.sf.saxon.pattern.AnchorPattern

All Implemented Interfaces:

ExportAgent, Locatable, IdentityComparable

Direct Known Subclasses:

CurrentGroupPattern

public class AnchorPattern
extends Pattern

This is a special pattern that matches the "anchor node". It is used for the selectors that arise when evaluating XPath expressions in streaming mode; the anchor node is the context node for the streamed XPath evaluation. Given a streamed evaluation of an expression such as ./BOOKS/BOOK/PRICE, the way we evaluate this is to turn it into a pattern, which is then tested against all descendant nodes. Conceptually the pattern is $A/BOOKS/BOOK/PRICE, where $A is referred to as the anchor node. When we evaluate the pattern against (say) a PRICE element, the match will only succeed if the name of the element is "PRICE" and its ancestors are, in order, a BOOK element, a BOOKS element, and the anchor node $A.

Field Summary

Fields inherited from class net.sf.saxon.expr.Expression

EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, MAX_COST, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, UPDATE_METHOD, WATCH_METHOD

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	AnchorPattern()

Method Summary

Modifier and Type	Method and Description
Pattern	copy(RebindingMap rebindings) Copy an AnchorPattern.
void	export(ExpressionPresenter presenter) Diagnostic print of expression structure.
static AnchorPattern	getInstance()
ItemType	getItemType() Get a NodeTest that all the nodes matching this pattern must satisfy
UType	getUType() Get a UType indicating which kinds of items this Pattern can match.
boolean	matches(Item<?> item, XPathContext context) Determine whether this Pattern matches the given Node.
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.
java.lang.String	toString() Get a string representation of the pattern.
Pattern	typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType) Type-check the pattern.

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

allocateSlots, bindCurrent, convertToTypedPattern, effectiveBooleanValue, getDefaultPriority, getDependencies, getFingerprint, getHostLanguage, handleDynamicError, isLiftable, isMotionless, isRecoverable, make, matchesCurrentGroup, optimize, patternContainsVariable, replaceCurrent, selectNodes, setOriginalText, setPriority, setRecoverable, simplify, toShortString

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

computeCardinality, evaluateAsString, evaluateItem, getImplementationMethod, iterate, process

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

addToPathMap, adoptChildExpression, allowExtractingCommonSubexpressions, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeHashCode, computeSpecialProperties, computeStaticProperties, dynamicError, equals, evaluatePendingUpdates, explain, getCardinality, getConfiguration, getConstructType, getCost, getEvaluationMethod, getExpressionName, getExtraProperty, getIntegerBounds, getInterpretedExpression, getIntrinsicDependencies, getLocalRetainedStaticContext, getLocation, getNetCost, getObjectName, getPackageData, getParentExpression, getProperties, getProperty, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, getStaticUType, getStreamerName, hasCompatibleStaticContext, hashCode, hasSpecialProperty, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isEqual, isIdentical, isInstruction, isMultiThreaded, isStaticPropertiesKnown, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, markTailFunctionCalls, operandList, operands, operandSparseList, optimizeChildren, prepareForStreaming, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setExtraProperty, setFiltered, setFlattened, setLocation, setParentExpression, setRetainedStaticContext, setRetainedStaticContextLocally, setRetainedStaticContextThoroughly, setStaticProperty, simplifyChildren, staticTypeCheck, suppressValidation, toPattern, typeCheckChildren, typeError, unordered, verifyParentPointers

Methods inherited from class java.lang.Object

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

Constructor Detail

AnchorPattern

protected AnchorPattern()

Method Detail

getInstance

public static AnchorPattern getInstance()

getUType

public UType getUType()

Get a UType indicating which kinds of items this Pattern can match.

Specified by:

getUType in class Pattern

Returns:

a UType indicating all the primitive types of item that the pattern can match.

typeCheck

public Pattern typeCheck(ExpressionVisitor visitor,
                         ContextItemStaticInfo contextItemType)
                  throws XPathException

Type-check the pattern.

Overrides:

typeCheck in class Pattern

Parameters:

visitor - the expression visitor

contextItemType - the type of the context item at the point where the pattern is defined. Set to null if it is known that the context item is undefined.

Returns:

the optimised Pattern

Throws:

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

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)

matches

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

Determine whether this Pattern matches the given Node. This is the main external interface for matching patterns: it sets current() to the node being tested

Specified by:

matches in class Pattern

Parameters:

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

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)

getItemType

public ItemType getItemType()

Get a NodeTest that all the nodes matching this pattern must satisfy

Specified by:

getItemType in class Pattern

Returns:

a NodeTest, as specific as possible, which all the matching nodes satisfy

toString

public java.lang.String toString()

Description copied from class: Pattern

Get a string representation of the pattern. This will be in a form similar to the original pattern text, but not necessarily identical. It is not guaranteed to be in legal pattern syntax.

Overrides:

toString in class Pattern

Returns:

a representation of the expression as a string

export

public void export(ExpressionPresenter presenter)
            throws XPathException

Description copied from class: Expression

Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

Specified by:

export in interface ExportAgent

Specified by:

export in class Pattern

Parameters:

presenter - the expression presenter used to display the structure

Throws:

XPathException - if the export fails, for example if an expression is found that won't work in the target environment.

copy

public Pattern copy(RebindingMap rebindings)

Copy an AnchorPattern. Since there is only one, return the same.

Specified by:

copy in class Pattern

Parameters:

rebindings - variables that need to be re-bound

Returns:

the original nodeTest