Class Choose
- java.lang.Object
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- net.sf.saxon.expr.ComputedExpression
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- net.sf.saxon.instruct.Instruction
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- net.sf.saxon.instruct.Choose
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- All Implemented Interfaces:
java.io.Serializable
,javax.xml.transform.SourceLocator
,Container
,Expression
,TailCallReturner
,InstructionInfoProvider
public class Choose extends Instruction
Compiled representation of an xsl:choose or xsl:if element in the stylesheet. Also used for typeswitch in XQuery.- See Also:
- Serialized Form
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Field Summary
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Fields inherited from class net.sf.saxon.expr.ComputedExpression
locationId, staticProperties
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Fields inherited from interface net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
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Constructor Summary
Constructors Constructor Description Choose(Expression[] conditions, Expression[] actions)
Construct an xsl:choose instruction
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
checkPermittedContents(SchemaType parentType, StaticContext env, boolean whole)
Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type.boolean
createsNewNodes()
Determine whether this instruction creates new nodes.void
display(int level, java.io.PrintStream out, Configuration config)
Diagnostic print of expression structure.Item
evaluateItem(XPathContext context)
Evaluate an expression as a single item.int
getImplementationMethod()
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().int
getInstructionNameCode()
Get the name of this instruction for diagnostic and tracing purposes We assume that if there was only one condition then it was an xsl:if; this is not necessarily so, but it's adequate for tracing purposes.ItemType
getItemType(TypeHierarchy th)
Get the item type of the items returned by evaluating this instructionSequenceIterator
iterate(XPathContext context)
Return an Iterator to iterate over the values of a sequence.java.util.Iterator
iterateSubExpressions()
Get all the XPath expressions associated with this instruction (in XSLT terms, the expression present on attributes of the instruction, as distinct from the child instructions in a sequence construction)boolean
markTailFunctionCalls(int nameCode, int arity)
Mark tail calls on used-defined functions.Expression
optimize(Optimizer opt, StaticContext env, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.TailCall
processLeavingTail(XPathContext context)
Process this instruction, that is, choose an xsl:when or xsl:otherwise child and process it.protected void
promoteInst(PromotionOffer offer)
Handle promotion offers, that is, non-local tree rewrites.boolean
replaceSubExpression(Expression original, Expression replacement)
Replace one subexpression by a replacement subexpressionExpression
simplify(StaticContext env)
Simplify an expression.Expression
typeCheck(StaticContext env, ItemType contextItemType)
Perform type checking of an expression and its subexpressions.-
Methods inherited from class net.sf.saxon.instruct.Instruction
appendItem, assembleParams, assembleTunnelParams, computeCardinality, computeSpecialProperties, dynamicError, evaluateAsString, getInstructionInfo, getSourceLocator, isXSLT, process, promote
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Methods inherited from class net.sf.saxon.expr.ComputedExpression
adoptChildExpression, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getIntrinsicDependencies, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, resetStaticProperties, setLocationId, setParentExpression, setParentExpression, suppressValidation, typeError
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Constructor Detail
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Choose
public Choose(Expression[] conditions, Expression[] actions)
Construct an xsl:choose instruction- Parameters:
conditions
- the conditions to be tested, in orderactions
- the actions to be taken when the corresponding condition is true
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Method Detail
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getInstructionNameCode
public int getInstructionNameCode()
Get the name of this instruction for diagnostic and tracing purposes We assume that if there was only one condition then it was an xsl:if; this is not necessarily so, but it's adequate for tracing purposes.- Overrides:
getInstructionNameCode
in classInstruction
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simplify
public Expression simplify(StaticContext env) throws XPathException
Simplify an expression. This performs any static optimization (by rewriting the expression as a different expression).- Specified by:
simplify
in interfaceExpression
- Specified by:
simplify
in classInstruction
- Parameters:
env
- the static context- Returns:
- the simplified expression
- Throws:
XPathException
- if an error is discovered during expression rewriting
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typeCheck
public Expression typeCheck(StaticContext env, ItemType contextItemType) throws XPathException
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:
StaticError
- if an error is discovered during this phase (typically a type error)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:
StaticError
- if an error is discovered during this phase (typically a type error)XPathException
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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. For instructions this is the process() method.- Specified by:
getImplementationMethod
in interfaceExpression
- Overrides:
getImplementationMethod
in classInstruction
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markTailFunctionCalls
public boolean markTailFunctionCalls(int nameCode, int arity)
Mark tail calls on used-defined functions. For most expressions, this does nothing.- Overrides:
markTailFunctionCalls
in classComputedExpression
- Returns:
- true if a tail recursive call was found and if this call accounts for the whole of the value.
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getItemType
public ItemType getItemType(TypeHierarchy th)
Get the item type of the items returned by evaluating this instruction- Specified by:
getItemType
in interfaceExpression
- Overrides:
getItemType
in classInstruction
- Parameters:
th
-- Returns:
- the static item type of the instruction
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createsNewNodes
public final boolean createsNewNodes()
Determine whether this instruction creates new nodes. This implementation returns true if any of the "actions" creates new nodes. (Nodes created by the conditions can't contribute to the result).- Overrides:
createsNewNodes
in classInstruction
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iterateSubExpressions
public java.util.Iterator iterateSubExpressions()
Get all the XPath expressions associated with this instruction (in XSLT terms, the expression present on attributes of the instruction, as distinct from the child instructions in a sequence construction)- Specified by:
iterateSubExpressions
in interfaceExpression
- Overrides:
iterateSubExpressions
in classComputedExpression
- Returns:
- an iterator containing the sub-expressions of this expression
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replaceSubExpression
public boolean replaceSubExpression(Expression original, Expression replacement)
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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promoteInst
protected void promoteInst(PromotionOffer offer) throws XPathException
Handle promotion offers, that is, non-local tree rewrites.- Overrides:
promoteInst
in classInstruction
- Parameters:
offer
- The type of rewrite being offered- Throws:
XPathException
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checkPermittedContents
public void checkPermittedContents(SchemaType parentType, StaticContext env, boolean whole) throws XPathException
Check that any elements and attributes constructed or returned by this expression are acceptable in the content model of a given complex type. It's always OK to say yes, since the check will be repeated at run-time. The process of checking element and attribute constructors against the content model of a complex type also registers the type of content expected of those constructors, so the static validation can continue recursively.- Specified by:
checkPermittedContents
in interfaceExpression
- Overrides:
checkPermittedContents
in classComputedExpression
- 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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display
public void display(int level, java.io.PrintStream out, Configuration config)
Diagnostic print of expression structure. The expression is written to the System.err output stream- Parameters:
level
- indentation level for this expressionout
-config
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processLeavingTail
public TailCall processLeavingTail(XPathContext context) throws XPathException
Process this instruction, that is, choose an xsl:when or xsl:otherwise child and process it.- Specified by:
processLeavingTail
in interfaceTailCallReturner
- Specified by:
processLeavingTail
in classInstruction
- Parameters:
context
- the dynamic context of this transformation- Returns:
- a TailCall, if the chosen branch ends with a call of call-template or apply-templates. It is the caller's responsibility to execute such a TailCall. If there is no TailCall, returns null.
- Throws:
XPathException
- if any non-recoverable dynamic error occurs
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evaluateItem
public Item evaluateItem(XPathContext context) throws XPathException
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 classInstruction
- 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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iterate
public SequenceIterator iterate(XPathContext context) throws XPathException
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 relies on the process() method: it "pushes" the results of the instruction to a sequence in memory, and then iterates over this in-memory sequence. In principle instructions should implement a pipelined iterate() method that avoids the overhead of intermediate storage.- Specified by:
iterate
in interfaceExpression
- Overrides:
iterate
in classInstruction
- 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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