net.sf.saxon.expr

Class SubscriptExpression

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.UnaryExpression

net.sf.saxon.expr.SingleItemFilter

net.sf.saxon.expr.SubscriptExpression

All Implemented Interfaces:

Serializable, SourceLocator, LocationProvider, SaxonLocator, InstructionInfo, Locator

public class SubscriptExpression
extends SingleItemFilter

A SubscriptExpression represents a FilterExpression of the form EXPR[n] where n is known to be singleton numeric and to be independent of the focus; it does not need to be constant

See Also:

Serialized Form

Field Summary

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

operand

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

EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, EVENT_FEED_METHOD, INHERITED_CONTEXT, INSPECTION_CONTEXT, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, NAVIGATION_CONTEXT, NODE_VALUE_CONTEXT, PROCESS_METHOD, PUSH_SELECTION, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, W3C_CONSUMING, W3C_FREE_RANGING, W3C_GROUP_CONSUMING, W3C_MOTIONLESS, WATCH_METHOD

Constructor Summary

Constructors

Constructor and Description
SubscriptExpression(Expression base, Expression subscript) Construct a SubscriptExpression

Method Summary

Methods

Modifier and Type	Method and Description
int	computeCardinality() Get the static cardinality: this implementation is appropriate for [1] and [last()] which will always return something if the input is non-empty
Expression	copy() Copy an expression.
boolean	equals(Object other) Compare two expressions to see if they are equal
Item	evaluateItem(XPathContext context) Evaluate an expression as a single item.
void	explain(ExpressionPresenter destination) Diagnostic print of expression structure.
ExpressionCompiler	getExpressionCompiler() Return the compiler of the TailExpression expression
Expression	getSubscriptExpression() Get the subscript expression
int	hashCode() get HashCode for comparing two expressions.
Iterator<Expression>	iterateSubExpressions() Get the immediate subexpressions of this expression
Expression	optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) Perform optimisation of an expression and its subexpressions.
Expression	promote(PromotionOffer offer, Expression parent) Promote this expression if possible
boolean	replaceSubExpression(Expression original, Expression replacement) Replace one subexpression by a replacement subexpression
Pattern	toStreamingPattern(Configuration config, List<String> reasonForFailure) Convert this expression to a streaming pattern (a pattern used internally to match nodes during push processing of an event stream)
String	toString() The toString() method for an expression attempts to give a representation of the expression in an XPath-like form.
Expression	typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) Type-check the expression.

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

computeSpecialProperties, displayOperator, getBaseExpression, getItemType, simplify

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

addToPathMap, adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getEvaluationMethod, getExecutable, getExpressionName, getHostLanguage, getImplementationMethod, getIntegerBounds, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getStreamability, getStreamingAdjunct, getSystemId, getSystemId, hasVariableBinding, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterate, iterateEvents, iterateSubExpressionInfo, markTailFunctionCalls, process, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, toPattern, typeError

Methods inherited from class java.lang.Object

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

Constructor Detail

SubscriptExpression

public SubscriptExpression(Expression base,
                   Expression subscript)

Construct a SubscriptExpression

Parameters:

base - the expression to be filtered

subscript - the positional subscript filter

Method Detail

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                   ExpressionVisitor.ContextItemType contextItemType)
                     throws XPathException

Description copied from class: UnaryExpression

Type-check the expression. Default implementation for unary operators that accept any kind of operand

Overrides:

typeCheck in class UnaryExpression

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 to perform necessary run-time type checks, and to perform other type-related optimizations

Throws:

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

optimize

public Expression optimize(ExpressionVisitor visitor,
                  ExpressionVisitor.ContextItemType contextItemType)
                    throws XPathException

Description copied from class: SingleItemFilter

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 SingleItemFilter

Parameters:

visitor - an expresion 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)

promote

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

Description copied from class: SingleItemFilter

Promote this expression if possible

Overrides:

promote in class SingleItemFilter

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 - the containing expression in the expression tree

Returns:

if the offer is not accepted, return this expression unchanged. Otherwise return the result of rewriting the expression to promote this subexpression

Throws:

XPathException - if any error is detected

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

iterateSubExpressions

public Iterator<Expression> iterateSubExpressions()

Description copied from class: UnaryExpression

Get the immediate subexpressions of this expression

Overrides:

iterateSubExpressions in class UnaryExpression

Returns:

an iterator containing the sub-expressions of this expression

replaceSubExpression

public boolean replaceSubExpression(Expression original,
                           Expression replacement)

Replace one subexpression by a replacement subexpression

Overrides:

replaceSubExpression in class UnaryExpression

Parameters:

original - the original subexpression

replacement - the replacement subexpression

Returns:

true if the original subexpression is found

getSubscriptExpression

public Expression getSubscriptExpression()

Get the subscript expression

Returns:

the expression used to compute the one-based start offset

equals

public boolean equals(Object other)

Compare two expressions to see if they are equal

Overrides:

equals in class UnaryExpression

Parameters:

other - the other expression

Returns:

true if the expressions are equivalent

hashCode

public int hashCode()

Description copied from class: UnaryExpression

get HashCode for comparing two expressions. Note that this hashcode gives the same result for (A op B) and for (B op A), whether or not the operator is commutative.

Overrides:

hashCode in class UnaryExpression

computeCardinality

public int computeCardinality()

Get the static cardinality: this implementation is appropriate for [1] and [last()] which will always return something if the input is non-empty

Overrides:

computeCardinality in class SingleItemFilter

Returns:

the computed cardinality, as one of the values StaticProperty.ALLOWS_ZERO_OR_ONE, StaticProperty.EXACTLY_ONE, StaticProperty.ALLOWS_ONE_OR_MORE, StaticProperty.ALLOWS_ZERO_OR_MORE

toStreamingPattern

public Pattern toStreamingPattern(Configuration config,
                         List<String> reasonForFailure)

Convert this expression to a streaming pattern (a pattern used internally to match nodes during push processing of an event stream)

Overrides:

toStreamingPattern in class Expression

Parameters:

config - the Saxon configuration

reasonForFailure - a list which will be populated with messages giving reasons why the expression cannot be converted

Returns:

the equivalent pattern if conversion succeeds; otherwise null

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException

Description copied from class: Expression

Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.

Overrides:

evaluateItem in class Expression

Parameters:

context - The context in which the expression is to be evaluated

Returns:

the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence

Throws:

XPathException - if any dynamic error occurs evaluating the expression

getExpressionCompiler

public ExpressionCompiler getExpressionCompiler()

Return the compiler of the TailExpression expression

Overrides:

getExpressionCompiler in class Expression

Returns:

the relevant ExpressionCompiler

explain

public void explain(ExpressionPresenter destination)

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

Overrides:

explain in class UnaryExpression

Parameters:

destination - the expression presenter used to display the structure

toString

public String toString()

The toString() method for an expression attempts to give a representation of the expression in an XPath-like form.

For subclasses of Expression that represent XPath expressions, the result should always be a string that parses as an XPath 3.0 expression.

Overrides:

toString in class UnaryExpression

Returns:

a representation of the expression as a string