net.sf.saxon.expr

Class TailExpression

java.lang.Object

net.sf.saxon.expr.Expression

net.sf.saxon.expr.UnaryExpression

net.sf.saxon.expr.TailExpression

All Implemented Interfaces:

IdentityComparable

public class TailExpression
extends UnaryExpression

A TailExpression represents a FilterExpression of the form EXPR[position() > n] Here n is usually 2, but we allow other values

Field Summary

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

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

Constructor Summary

Constructors

Constructor and Description
TailExpression(Expression base, int start) Construct a TailExpression, representing a filter expression of the form $base[position() >= $start]

Method Summary

Methods

Modifier and Type	Method and Description
int	computeCardinality() Determine the static cardinality.
Expression	copy() Copy an expression.
boolean	equals(Object other) Compare two expressions to see if they are equal
void	export(ExpressionPresenter destination) Diagnostic print of expression structure.
ExpressionCompiler	getExpressionCompiler() Return the compiler of the TailExpression expression
int	getImplementationMethod() An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().
ItemType	getItemType() Determine the data type of the expression, if possible.
protected OperandRole	getOperandRole() Get the usage (in terms of streamability analysis) of the single operand
int	getStart() Get the start offset
StreamingAdjunct	getStreamingAdjunct() Get a class that supports streamed evaluation of this expression
int	hashCode() get HashCode for comparing two expressions.
SequenceIterator	iterate(XPathContext context) Return an Iterator to iterate over the values of a sequence.
Expression	optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) Perform optimisation of an expression and its subexpressions.
String	toShortString() Produce a short string identifying the expression for use in error messages
String	toString() The toString() method for an expression attempts to give a representation of the expression in an XPath-like form.

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

computeSpecialProperties, displayOperator, getBaseExpression, getOperand, operands, setBaseExpression, typeCheck

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

addToPathMap, adoptChildExpression, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, clearStreamabilityData, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, evaluatePendingUpdates, explain, getCardinality, getConfiguration, getConstructType, getCost, getDependencies, getEvaluationMethod, getExpressionName, getHostLanguage, getIntegerBounds, getIntrinsicDependencies, getLocation, getNetCost, getObjectName, getPackageData, getParentExpression, getPosture, getPostureAndSweepIfKnown, getProperties, getProperty, getRetainedStaticContext, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStreamability, getSweep, getSystemId, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isCallOnSystemFunction, isIdentical, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, iterateEvents, makeStreamingAdjunct, markTailFunctionCalls, operandList, operandSparseList, optimizeChildren, optimizeForType, process, promote, promoteChildren, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setFiltered, setFlattened, setLocation, setParentExpression, setPostureAndSweep, setRetainedStaticContext, setRetainedStaticContextLocally, setStaticProperty, simplify, simplifyChildren, staticTypeCheck, suppressValidation, toPattern, toStreamingPattern, typeCheckChildren, typeError, unordered

Methods inherited from class java.lang.Object

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

Constructor Detail

TailExpression

public TailExpression(Expression base,
              int start)

Construct a TailExpression, representing a filter expression of the form $base[position() >= $start]

Parameters:

base - the expression to be filtered

start - the position (1-based) of the first item to be included

Method Detail

optimize

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

Description copied from class: UnaryExpression

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 UnaryExpression

Parameters:

visitor - an expression 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()

Copy an expression. This makes a deep copy.

Specified by:

copy in class Expression

Returns:

the copy of the original expression

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

getItemType

public ItemType getItemType()

Description copied from class: UnaryExpression

Determine the data type of the expression, if possible. The default implementation for unary expressions returns the item type of the operand

Overrides:

getItemType in class UnaryExpression

Returns:

the item type of the items in the result sequence, insofar as this is known statically.

computeCardinality

public int computeCardinality()

Description copied from class: UnaryExpression

Determine the static cardinality. Default implementation returns the cardinality of the operand

Overrides:

computeCardinality in class UnaryExpression

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

getOperandRole

protected OperandRole getOperandRole()

Description copied from class: UnaryExpression

Get the usage (in terms of streamability analysis) of the single operand

Specified by:

getOperandRole in class UnaryExpression

Returns:

the operand usage

getStart

public int getStart()

Get the start offset

Returns:

the one-based start offset (returns 2 if all but the first item is being selected)

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

getStreamingAdjunct

public StreamingAdjunct getStreamingAdjunct()

Get a class that supports streamed evaluation of this expression

Overrides:

getStreamingAdjunct in class Expression

Returns:

the relevant StreamingAdjunct, or null if none is available

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException

Description copied from class: Expression

Return an Iterator to iterate over the values of a sequence. The value of every expression can be regarded as a sequence, so this method is supported for all expressions. This default implementation handles iteration for expressions that return singleton values: for non-singleton expressions, the subclass must provide its own implementation.

Overrides:

iterate in class Expression

Parameters:

context - supplies the context for evaluation

Returns:

a SequenceIterator that can be used to iterate over the result of the expression

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

export

public void export(ExpressionPresenter destination)

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

Overrides:

export 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

toShortString

public String toShortString()

Produce a short string identifying the expression for use in error messages

Overrides:

toShortString in class UnaryExpression

Returns:

a short string, sufficient to identify the expression