Interface Expression
- All Superinterfaces:
Serializable
- All Known Implementing Classes:
Adjust
,Aggregate
,AnalyzeString
,AnyURIValue
,ApplyImports
,ApplyTemplates
,ArithmeticExpression
,ArithmeticExpression.DateAndDuration
,ArithmeticExpression.DateDifference
,ArithmeticExpression.DurationAddition
,ArithmeticExpression.DurationDivision
,ArithmeticExpression.DurationMultiplication
,ArithmeticExpression.NumericArithmetic
,Assign
,Assignation
,AtomicSequenceConverter
,AtomicValue
,Atomizer
,Attribute
,Available
,AxisExpression
,Base64BinaryValue
,BaseURI
,BigIntegerValue
,BinaryExpression
,Block
,BooleanExpression
,BooleanFn
,BooleanValue
,CalendarValue
,CallTemplate
,CardinalityChecker
,CastableExpression
,CastExpression
,Choose
,Closure
,CodepointEqual
,CollatingFunction
,Collection
,Comment
,Compare
,CompareToIntegerConstant
,CompileTimeFunction
,Component
,ComputedElement
,ComputedExpression
,Concat
,Contains
,ContextItemExpression
,Copy
,CopyOf
,Current
,CurrentDateTime
,CurrentGroup
,CurrentItemExpression
,Data
,DateTimeConstructor
,DateTimeValue
,DateValue
,DecimalValue
,DeepEqual
,DefaultCollation
,DistinctValues
,Doc
,Doctype
,Document
,DocumentInstr
,DocumentSorter
,DoubleValue
,DurationValue
,EagerLetExpression
,ElementCreator
,EmptySequence
,Error
,ErrorExpression
,EscapeURI
,Evaluate
,Existence
,ExtensionFunctionCall
,FilterExpression
,FirstItemExpression
,FixedAttribute
,FixedElement
,FloatValue
,ForceCase
,ForEach
,ForEachGroup
,ForExpression
,FormatDate
,FormatNumber2
,FunctionCall
,GDayValue
,GeneralComparison
,GeneralComparison10
,GeneralVariable
,GlobalParam
,GlobalVariable
,GMonthDayValue
,GMonthValue
,GYearMonthValue
,GYearValue
,HexBinaryValue
,Id
,IdentityComparison
,Idref
,IfExpression
,IndexOf
,InScopePrefixes
,Insert
,InstanceOfExpression
,Instruction
,IntegerRange
,IntegerRangeTest
,IntegerValue
,IsLastExpression
,ItemChecker
,KeyFn
,Lang
,Last
,LazyExpression
,LetExpression
,LocalParam
,LocalVariable
,LocalVariableReference
,Matches
,MemoClosure
,Message
,Minimax
,MonthDurationValue
,NamePart
,Namespace
,NamespaceForPrefix
,NextMatch
,Nilled
,NormalizeSpace
,NormalizeUnicode
,NotationValue
,NumberFn
,NumberInstruction
,NumericPromoter
,NumericValue
,ObjectValue
,ParentNodeConstructor
,ParentNodeExpression
,Parse
,PathExpression
,PatternSponsor
,Position
,PositionRange
,ProcessingInstruction
,QNameFn
,QNameValue
,QuantifiedExpression
,QuerySimpleContentConstructor
,RangeExpression
,RegexGroup
,Remove
,Replace
,ResolveQName
,ResolveURI
,RestrictedStringValue
,ResultDocument
,Reverse
,Reverser
,Root
,RootExpression
,Rounding
,SecondsDurationValue
,SequenceExtent
,Serialize
,ShareableSequence
,SimpleContentConstructor
,SimpleExpression
,SimpleMappingExpression
,SimpleNodeConstructor
,SingleNodeExpression
,SingletonAtomizer
,SingletonComparison
,SingletonNode
,SliceExpression
,SortExpression
,SQLColumn.ColumnInstruction
,StaticBaseURI
,StringFn
,StringJoin
,StringLength
,StringValue
,Subsequence
,Substring
,SuppliedParameterReference
,SystemFunction
,SystemProperty
,TailCallLoop
,TailExpression
,TimeValue
,Tokenize
,Trace
,TraceExpression
,TraceInstruction
,TraceWrapper
,Translate
,TreatFn
,TupleExpression
,TupleSorter
,UnaryExpression
,Unicode
,Unordered
,UnparsedEntity
,UnparsedText
,UntypedAtomicConverter
,UntypedAtomicValue
,UseAttributeSets
,UserFunctionCall
,ValidationErrorValue
,Value
,ValueComparison
,ValueOf
,VariableReference
,VennExpression
,While
,WithParam
,XPathFunctionCall
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Field Summary
FieldsModifier and TypeFieldDescriptionstatic final int
static final int
static final int
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Method Summary
Modifier and TypeMethodDescriptionvoid
checkPermittedContents
(SchemaType parentType, StaticContext env, boolean whole) Check statically that the results of the expression are capable of constructing the content of a given schema type.void
display
(int level, PrintStream out, Configuration config) Diagnostic print of expression structure.boolean
effectiveBooleanValue
(XPathContext context) Get the effective boolean value of the expression.evaluateAsString
(XPathContext context) Evaluate an expression as a String.evaluateItem
(XPathContext context) Evaluate an expression as a single item.int
Determine the static cardinality of the expression.int
Determine which aspects of the context the expression depends on.int
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().Determine the data type of the expression, if possible.Get the container that immediately contains this expression.int
Get the static properties of this expression (other than its type).iterate
(XPathContext context) Return an Iterator to iterate over the values of a sequence.Get the immediate sub-expressions of this expression.optimize
(Optimizer opt, StaticContext env, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.void
process
(XPathContext context) Evaluate the expression in "push" mode: the results of evaluating the expression are sent to theReceiver
registered as part of the supplied context.promote
(PromotionOffer offer) Offer promotion for this subexpression.simplify
(StaticContext env) Simplify an expression.typeCheck
(StaticContext env, ItemType contextItemType) Perform type checking of an expression and its subexpressions.
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Field Details
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EVALUATE_METHOD
static final int EVALUATE_METHOD- See Also:
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ITERATE_METHOD
static final int ITERATE_METHOD- See Also:
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PROCESS_METHOD
static final int PROCESS_METHOD- See Also:
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Method Details
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getImplementationMethod
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. -
simplify
Simplify an expression. This performs the first phase static optimization (by rewriting the expression as a different expression). The default implementation does nothing.- Parameters:
env
- the static context- Returns:
- the simplified expression. If this is a different expression from the original, the implementation is responsible for setting up (a) the location information in the new expression, and (b) its parent pointer in the expression tree [which can generally be initialized using getParentExpression()]
- Throws:
StaticError
- if an error is discovered during expression rewritingXPathException
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typeCheck
Perform type checking of an expression and its subexpressions. This is the second phase of static optimization.This checks statically that the operands of the expression have the correct type; if necessary it generates code to do run-time type checking or type conversion. A static type error is reported only if execution cannot possibly succeed, that is, if a run-time type error is inevitable. The call may return a modified form of the expression.
This method is called after all references to functions and variables have been resolved to the declaration of the function or variable. However, the types of such functions and variables may not be accurately known if they have not been explicitly declared.
If the implementation returns a value other than "this", then it is required to ensure that the parent pointer and location information in the returned expression have been set up correctly. It should not rely on the caller to do this, although for historical reasons many callers do so.
- Parameters:
env
- the static context of the expressioncontextItemType
- 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 to perform necessary run-time type checks, and to perform other type-related optimizations
- Throws:
StaticError
- if an error is discovered during this phase (typically a type error)XPathException
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optimize
Expression optimize(Optimizer opt, StaticContext env, ItemType contextItemType) throws XPathException Perform optimisation of an expression and its subexpressions. This is the third and final phase of static optimization.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.
- Parameters:
opt
- the optimizer in use. This provides access to supporting functions; it also allows different optimization strategies to be used in different circumstances.env
- the static context of the expressioncontextItemType
- 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:
StaticError
- if an error is discovered during this phase (typically a type error)XPathException
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promote
Offer promotion for this subexpression. The offer will be accepted if the subexpression is not dependent on the factors (e.g. the context item) identified in the PromotionOffer. By default the offer is not accepted - this is appropriate in the case of simple expressions such as constant values and variable references where promotion would give no performance advantage. This method is always called at compile time.- 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- 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
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getSpecialProperties
int getSpecialProperties()Get the static properties of this expression (other than its type). The result is bit-signficant. These properties are used for optimizations. In general, if property bit is set, it is true, but if it is unset, the value is unknown.- Returns:
- a set of flags indicating static properties of this expression
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getCardinality
int getCardinality()Determine the static cardinality of the expression. This establishes how many items there will be in the result of the expression, at compile time (i.e., without actually evaluating the result.
This method should always return a result, though it may be the best approximation that is available at the time.
- Returns:
- one of the values
StaticProperty.ALLOWS_ONE
,StaticProperty.ALLOWS_ZERO_OR_MORE
,StaticProperty.ALLOWS_ZERO_OR_ONE
,StaticProperty.ALLOWS_ONE_OR_MORE
,StaticProperty.EMPTY
. This default implementation returns ZERO_OR_MORE (which effectively gives no information).
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getItemType
Determine the data type of the expression, if possible. All expression return sequences, in general; this method determines the type of the items within the sequence, assuming that (a) this is known in advance, and (b) it is the same for all items in the sequence.This method should always return a result, though it may be the best approximation that is available at the time.
- Parameters:
th
-- Returns:
- a value such as Type.STRING, Type.BOOLEAN, Type.NUMBER, Type.NODE, or Type.ITEM (meaning not known at compile time)
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getDependencies
int getDependencies()Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such asStaticProperty.DEPENDS_ON_CONTEXT_ITEM
andStaticProperty.DEPENDS_ON_CURRENT_ITEM
. The default implementation combines the intrinsic dependencies of this expression with the dependencies of the subexpressions, computed recursively. This is overridden for expressions such as FilterExpression where a subexpression's dependencies are not necessarily inherited by the parent expression.- Returns:
- a set of bit-significant flags identifying the dependencies of the expression
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iterateSubExpressions
Iterator iterateSubExpressions()Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.- Returns:
- an iterator containing the sub-expressions of this expression
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getParentExpression
Container getParentExpression()Get the container that immediately contains this expression. This method returns null for an outermost expression; it also return null in the case of literal values. For an XPath expression occurring within an XSLT stylesheet, this method returns the XSLT instruction containing the XPath expression.- Returns:
- the expression that contains this expression, if known; return null if there is no containing expression or if the containing expression is unknown.
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evaluateItem
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.- Parameters:
context
- The context in which the expression is to be evaluated. Note that this context must contain a stackframe with sufficient slots to allow evaluation of any variables contained in the expression (including variables allocated internally by the optimizer)- 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
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iterate
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.- Parameters:
context
- The context in which the expression is to be evaluated. Note that this context must contain a stackframe with sufficient slots to allow evaluation of any variables contained in the expression (including variables allocated internally by the optimizer)- 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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effectiveBooleanValue
Get the effective boolean value of the expression. This returns false if the value is the empty sequence, a zero-length string, a number equal to zero, or the boolean false. Otherwise it returns true.- Parameters:
context
- The context in which the expression is to be evaluated. Note that this context must contain a stackframe with sufficient slots to allow evaluation of any variables contained in the expression (including variables allocated internally by the optimizer)- Returns:
- the effective boolean value
- Throws:
XPathException
- if any dynamic error occurs evaluating the expression
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evaluateAsString
Evaluate an expression as a String. This function must only be called in contexts where it is known that the expression will return a single string (or where an empty sequence is to be treated as a zero-length string). Implementations should not attempt to convert the result to a string, other than converting () to "". This method is used mainly to evaluate expressions produced by compiling an attribute value template.- Parameters:
context
- The context in which the expression is to be evaluated. Note that this context must contain a stackframe with sufficient slots to allow evaluation of any variables contained in the expression (including variables allocated internally by the optimizer)- Returns:
- the value of the expression, evaluated in the current context. The expression must return a string or (); if the value of the expression is (), this method returns "".
- Throws:
XPathException
- if any dynamic error occurs evaluating the expressionClassCastException
- if the result type of the expression is not xs:string?
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process
Evaluate the expression in "push" mode: the results of evaluating the expression are sent to theReceiver
registered as part of the supplied context.- Parameters:
context
- The context in which the expression is to be evaluated. Note that this context must contain a stackframe with sufficient slots to allow evaluation of any variables contained in the expression (including variables allocated internally by the optimizer)- Throws:
XPathException
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display
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.- Parameters:
level
- indentation level for this expressionout
- Output destinationconfig
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checkPermittedContents
void checkPermittedContents(SchemaType parentType, StaticContext env, boolean whole) throws XPathException Check statically that the results of the expression are capable of constructing the content of a given schema type.- Parameters:
parentType
- The schema typeenv
- the static contextwhole
- true if this expression is expected to make the whole content of the type, false if it is expected to make up only a part- Throws:
XPathException
- if the expression doesn't match the required content type
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