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:

ExportAgent, Locatable, IdentityComparable

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

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

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

Method Summary

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
int	computeHashCode() get HashCode for comparing two expressions.
Expression	copy(RebindingMap rebindings) Copy an expression.
boolean	equals(java.lang.Object other) Compare two expressions to see if they are equal
Item	evaluateItem(XPathContext context) Evaluate an expression as a single item.
void	export(ExpressionPresenter destination) Diagnostic print of expression structure.
java.lang.String	getExpressionName() Get a name identifying the kind of expression, in terms meaningful to a user.
int	getImplementationMethod() An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
java.lang.String	getStreamerName() Get the (partial) name of a class that supports streaming of this kind of expression
Expression	getSubscript()
Expression	getSubscriptExpression() Get the subscript expression
java.lang.Iterable<Operand>	operands() Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression.
Expression	optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) Perform optimisation of an expression and its subexpressions.
void	setSubscript(Expression subscript)
java.lang.String	toShortString() The toString() method for an expression attempts to give a representation of the expression in an XPath-like form.
java.lang.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, ContextItemStaticInfo contextInfo) Type-check the expression.

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

getOperandRole

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

computeSpecialProperties, displayOperator, getBaseExpression, getItemType, getOperand, setBaseExpression

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

addToPathMap, adoptChildExpression, allowExtractingCommonSubexpressions, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, dynamicError, effectiveBooleanValue, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getConfiguration, getConstructType, getCost, getDependencies, getEvaluationMethod, getExtraProperty, getIntegerBounds, getInterpretedExpression, getIntrinsicDependencies, getLocalRetainedStaticContext, getLocation, getNetCost, getObjectName, getPackageData, getParentExpression, getProperties, getProperty, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, getStaticUType, hasCompatibleStaticContext, hashCode, hasSpecialProperty, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isEqual, isIdentical, isInstruction, isLiftable, isMultiThreaded, isStaticPropertiesKnown, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterate, markTailFunctionCalls, operandList, operandSparseList, optimizeChildren, prepareForStreaming, process, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setExtraProperty, setFiltered, setFlattened, setLocation, setParentExpression, setRetainedStaticContext, setRetainedStaticContextLocally, setRetainedStaticContextThoroughly, setStaticProperty, simplify, 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

SubscriptExpression

public SubscriptExpression(Expression base,
                           Expression subscript)

Construct a SubscriptExpression

Parameters:

base - the expression to be filtered

subscript - the positional subscript filter

Method Detail

getSubscript

public Expression getSubscript()

setSubscript

public void setSubscript(Expression subscript)

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ContextItemStaticInfo contextInfo)
                     throws XPathException

Type-check the expression.

Overrides:

typeCheck in class UnaryExpression

Parameters:

visitor - an expression visitor

contextInfo - Information available statically about the context item: whether it is (possibly) absent; its static type; its streaming posture.

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,
                           ContextItemStaticInfo contextInfo)
                    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

contextInfo - 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)

copy

public Expression copy(RebindingMap rebindings)

Copy an expression. This makes a deep copy.

Specified by:

copy in class Expression

Parameters:

rebindings - variables that need to be re-bound

Returns:

the copy of the original expression

operands

public java.lang.Iterable<Operand> operands()

Description copied from class: Expression

Get the immediate sub-expressions of this expression, with information about the relationship of each expression to its parent expression. Default implementation works off the results of iterateSubExpressions()

If the expression is a Callable, then it is required that the order of the operands returned by this function is the same as the order of arguments supplied to the corresponding call() method.

Overrides:

operands in class UnaryExpression

Returns:

an iterator containing the sub-expressions of this expression

getSubscriptExpression

public Expression getSubscriptExpression()

Get the subscript expression

Returns:

the expression used to compute the one-based start offset

getImplementationMethod

public int getImplementationMethod()

An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process(). This method indicates which of these methods is provided directly. The other methods will always be available indirectly, using an implementation that relies on one of the other methods.

Specified by:

getImplementationMethod in class Expression

Returns:

the implementation method, for example Expression.ITERATE_METHOD or Expression.EVALUATE_METHOD or Expression.PROCESS_METHOD

equals

public boolean equals(java.lang.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

computeHashCode

public int computeHashCode()

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:

computeHashCode in class UnaryExpression

Returns:

a computed hash code

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. May also return StaticProperty.ALLOWS_ZERO if the result is known to be an empty sequence, or StaticProperty.ALLOWS_MANY if if is known to return a sequence of length two or more.

getStreamerName

public java.lang.String getStreamerName()

Get the (partial) name of a class that supports streaming of this kind of expression

Overrides:

getStreamerName in class Expression

Returns:

the partial name of a class that can be instantiated to provide streaming support in Saxon-EE, or null if there is no such class

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

getExpressionName

public java.lang.String getExpressionName()

Get a name identifying the kind of expression, in terms meaningful to a user.

Overrides:

getExpressionName in class Expression

Returns:

a name identifying the kind of expression, in terms meaningful to a user. The name will always be in the form of a lexical XML QName, and should match the name used in export() output displaying the expression.

export

public void export(ExpressionPresenter destination)
            throws XPathException

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

Specified by:

export in interface ExportAgent

Overrides:

export in class UnaryExpression

Parameters:

destination - 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.

toString

public java.lang.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

toShortString

public java.lang.String toShortString()

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:

toShortString in class UnaryExpression

Returns:

a representation of the expression as a string