Class SimpleContentConstructor
- All Implemented Interfaces:
Serializable
,SourceLocator
,Container
,Expression
,InstructionInfoProvider
- Direct Known Subclasses:
QuerySimpleContentConstructor
- See Also:
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Field Summary
FieldsModifier and TypeFieldDescription(package private) boolean
(package private) boolean
(package private) Expression
(package private) Expression
Fields inherited from class net.sf.saxon.expr.ComputedExpression
locationId, staticProperties
Fields inherited from interface net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionprotected int
Compute the cardinality of the result of the expression.void
display
(int level, PrintStream out, Configuration config) Diagnostic print of expression structure.evaluateItem
(XPathContext context) Evaluate an expression as a single item.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 immediate sub-expressions of this expression.optimize
(Optimizer opt, StaticContext env, ItemType contextItemType) Perform optimisation of an expression and its subexpressions.promote
(PromotionOffer offer) Offer promotion for this subexpression.boolean
replaceSubExpression
(Expression original, Expression replacement) Replace one subexpression by a replacement subexpressionsimplify
(StaticContext env) Simplify an expression.typeCheck
(StaticContext env, ItemType contextItemType) Perform type checking of an expression and its subexpressions.Methods inherited from class net.sf.saxon.expr.ComputedExpression
adoptChildExpression, checkPermittedContents, computeDependencies, computeSpecialProperties, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getInstructionInfo, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, iterate, markTailFunctionCalls, process, resetStaticProperties, setLocationId, setParentExpression, setParentExpression, suppressValidation, typeError
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Field Details
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select
Expression select -
separator
Expression separator -
isSingleton
boolean isSingleton -
isAtomic
boolean isAtomic
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Constructor Details
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SimpleContentConstructor
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Method Details
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computeCardinality
protected int computeCardinality()Compute the cardinality of the result of the expression.- Specified by:
computeCardinality
in classComputedExpression
- Returns:
- the cardinality, @link {StaticProperty.EXACTLY_ONE}
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typeCheck
Description copied from interface:Expression
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:
XPathException
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optimize
public Expression optimize(Optimizer opt, StaticContext env, ItemType contextItemType) throws XPathException Description copied from interface:Expression
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:
XPathException
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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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display
Diagnostic print of expression structure. The expression is written to the System.err output stream- Parameters:
level
- indentation level for this expressionout
- Output destinationconfig
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simplify
Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression). The default implementation does nothing.- Specified by:
simplify
in interfaceExpression
- Overrides:
simplify
in classComputedExpression
- Parameters:
env
- the static context- Returns:
- the simplified expression
- Throws:
XPathException
- if an error is discovered during expression rewriting
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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.- Specified by:
iterateSubExpressions
in interfaceExpression
- Overrides:
iterateSubExpressions
in classComputedExpression
- Returns:
- an iterator containing the sub-expressions of this expression
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replaceSubExpression
Replace one subexpression by a replacement subexpression- Specified by:
replaceSubExpression
in interfaceContainer
- Overrides:
replaceSubExpression
in classComputedExpression
- Parameters:
original
- the original subexpressionreplacement
- the replacement subexpression- Returns:
- true if the original subexpression is found
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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.- Specified by:
promote
in interfaceExpression
- Overrides:
promote
in classComputedExpression
- 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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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.- Specified by:
evaluateItem
in interfaceExpression
- Overrides:
evaluateItem
in classComputedExpression
- 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
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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 prefered.- Specified by:
getImplementationMethod
in interfaceExpression
- Overrides:
getImplementationMethod
in classComputedExpression
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