Package net.sf.saxon.expr
Class TailExpression
- java.lang.Object
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- net.sf.saxon.expr.Expression
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- net.sf.saxon.expr.UnaryExpression
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- net.sf.saxon.expr.TailExpression
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- All Implemented Interfaces:
ExportAgent,Locatable,IdentityComparable,Traceable
public class TailExpression extends UnaryExpression
A TailExpression represents a FilterExpression of the formEXPR[position() > n]Here n is usually 2, but we allow other values
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Field Summary
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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
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Constructor Summary
Constructors Constructor Description TailExpression(Expression base, int start)Construct a TailExpression, representing a filter expression of the form$base[position() >= $start]
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description intcomputeCardinality()Determine the static cardinality.intcomputeHashCode()get HashCode for comparing two expressions.Expressioncopy(RebindingMap rebindings)Copy an expression.booleanequals(java.lang.Object other)Compare two expressions to see if they are equalvoidexport(ExpressionPresenter destination)Diagnostic print of expression structure.java.lang.StringgetExpressionName()Get a name identifying the kind of expression, in terms meaningful to a user.intgetImplementationMethod()An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().ItemTypegetItemType()Determine the data type of the expression, if possible.protected OperandRolegetOperandRole()Get the usage (in terms of streamability analysis) of the single operandintgetStart()Get the start offsetjava.lang.StringgetStreamerName()Get the (partial) name of a class that supports streaming of this kind of expressionSequenceIteratoriterate(XPathContext context)Return an Iterator to iterate over the values of a sequence.Expressionoptimize(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo)Perform optimisation of an expression and its subexpressions.java.lang.StringtoShortString()Produce a short string identifying the expression for use in error messagesjava.lang.StringtoString()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, emitExtraAttributes, getBaseExpression, getOperand, operands, setBaseExpression, typeCheck
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Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, allowExtractingCommonSubexpressions, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, evaluatePendingUpdates, explain, getCardinality, getConfiguration, getCost, getDependencies, getEvaluationMethod, getExtraProperty, getIntegerBounds, getInterpretedExpression, getIntrinsicDependencies, getLocalRetainedStaticContext, getLocation, getNetCost, getObjectName, getPackageData, getParentExpression, getProperties, getProperty, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, getStaticUType, getTracingTag, hasCompatibleStaticContext, hashCode, hasSpecialProperty, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isEqual, isIdentical, isInstruction, isLiftable, isMultiThreaded, isStaticPropertiesKnown, isSubtreeExpression, isUpdatingExpression, isVacuousExpression, 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
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Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
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Methods inherited from interface net.sf.saxon.trace.Traceable
gatherProperties
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Constructor Detail
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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 filteredstart- the position (1-based) of the first item to be included
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Method Detail
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optimize
public Expression optimize(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) throws XPathException
Description copied from class:UnaryExpressionPerform 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:
optimizein classUnaryExpression- Parameters:
visitor- an expression visitorcontextInfo- 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 toType.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)
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copy
public Expression copy(RebindingMap rebindings)
Copy an expression. This makes a deep copy.- Specified by:
copyin classExpression- Parameters:
rebindings- variables that need to be re-bound- Returns:
- the copy of the original expression
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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:
getImplementationMethodin classExpression- Returns:
- the implementation method, for example
Expression.ITERATE_METHODorExpression.EVALUATE_METHODorExpression.PROCESS_METHOD
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getItemType
public ItemType getItemType()
Description copied from class:UnaryExpressionDetermine the data type of the expression, if possible. The default implementation for unary expressions returns the item type of the operand- Overrides:
getItemTypein classUnaryExpression- Returns:
- the item type of the items in the result sequence, insofar as this is known statically.
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computeCardinality
public int computeCardinality()
Description copied from class:UnaryExpressionDetermine the static cardinality. Default implementation returns the cardinality of the operand- Overrides:
computeCardinalityin classUnaryExpression- 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 returnStaticProperty.ALLOWS_ZEROif the result is known to be an empty sequence, orStaticProperty.ALLOWS_MANYif if is known to return a sequence of length two or more.
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getOperandRole
protected OperandRole getOperandRole()
Description copied from class:UnaryExpressionGet the usage (in terms of streamability analysis) of the single operand- Specified by:
getOperandRolein classUnaryExpression- Returns:
- the operand usage
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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)
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equals
public boolean equals(java.lang.Object other)
Compare two expressions to see if they are equal- Overrides:
equalsin classUnaryExpression- Parameters:
other- the other expression- Returns:
- true if the expressions are equivalent
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computeHashCode
public int computeHashCode()
Description copied from class:UnaryExpressionget 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:
computeHashCodein classUnaryExpression- Returns:
- a computed hash code
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getStreamerName
public java.lang.String getStreamerName()
Get the (partial) name of a class that supports streaming of this kind of expression- Overrides:
getStreamerNamein classExpression- 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
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iterate
public SequenceIterator iterate(XPathContext context) throws XPathException
Description copied from class:ExpressionReturn 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:
iteratein classExpression- 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
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getExpressionName
public java.lang.String getExpressionName()
Get a name identifying the kind of expression, in terms meaningful to a user.- Overrides:
getExpressionNamein classExpression- 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.
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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:
exportin interfaceExportAgent- Overrides:
exportin classUnaryExpression- 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.
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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:
toStringin classUnaryExpression- Returns:
- a representation of the expression as a string
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toShortString
public java.lang.String toShortString()
Produce a short string identifying the expression for use in error messages- Overrides:
toShortStringin classUnaryExpression- Returns:
- a short string, sufficient to identify the expression
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