Class Block
- All Implemented Interfaces:
Serializable
,SourceLocator
,LocationProvider
,SaxonLocator
,TailCallReturner
,InstructionInfo
,Locator
- See Also:
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Field Summary
Fields inherited from class net.sf.saxon.expr.Expression
EFFECTIVE_BOOLEAN_VALUE, EVALUATE_METHOD, EVENT_FEED_METHOD, ITEM_FEED_METHOD, ITERATE_METHOD, locationId, MAX_SEQUENCE_LENGTH, MAX_STRING_LENGTH, PROCESS_METHOD, PUSH_SELECTION, staticProperties, UNBOUNDED_LOWER, UNBOUNDED_UPPER, WATCH_METHOD
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Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionvoid
Check to ensure that this expression does not contain any updating subexpressions.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.int
Get the static properties of this expression (other than its type).copy()
Copy an expression.final boolean
Determine whether this instruction creates new nodes.void
evaluatePendingUpdates
(XPathContext context, PendingUpdateList pul) Evaluate an updating expression, adding the results to a Pending Update List.void
Diagnostic print of expression structure.final int
Determine the cardinality of the expressionGet the children of this instructionGet a name identifying the kind of expression, in terms meaningful to a user.int
An implementation of Expression must provide at least one of the methods evaluateItem(), iterate(), or process().final ItemType
Determine the data type of the items returned by this expressionboolean
Determine whether this is a vacuous expression as defined in the XQuery update specificationSequenceIterator
<? extends Item> iterate
(XPathContext context) Iterate over the results of all the child expressionsiterateEvents
(XPathContext context) Get an EventIterator over the results of all the child expressionsGet the immediate sub-expressions of this expression.static Expression
makeBlock
(List<Expression> list) Static factory method to create a block from a list of expressionsstatic Expression
makeBlock
(Expression e1, Expression e2) Static factory method to create a block.Merge any adjacent instructions that create literal text nodesoptimize
(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) Perform optimisation of an expression and its subexpressions.processLeavingTail
(XPathContext context) ProcessLeavingTail: called to do the real work of this instruction.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 subexpressionvoid
setChildren
(Expression[] children) Set the children of this instructionsimplify
(ExpressionVisitor visitor) Simplify an expression.typeCheck
(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) Perform type checking of an expression and its subexpressions.Methods inherited from class net.sf.saxon.expr.instruct.Instruction
assembleParams, assembleTunnelParams, computeCardinality, dynamicError, evaluateAsString, evaluateItem, getConstructType, getInstructionName, getInstructionNameCode, getIteratorFromProcessMethod, getSourceLocator, isXSLT, process, promote
Methods inherited from class net.sf.saxon.expr.Expression
addToPathMap, adoptChildExpression, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, explain, getColumnNumber, getColumnNumber, getContainer, getDependencies, getEvaluationMethod, getExecutable, getHostLanguage, getIntegerBounds, getIntrinsicDependencies, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, hasVariableBinding, implementsStaticTypeCheck, isSubtreeExpression, isUpdatingExpression, iterateSameFocusSubExpressions, markTailFunctionCalls, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, toString, typeError
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
Methods inherited from interface javax.xml.transform.SourceLocator
getColumnNumber, getLineNumber, getPublicId, getSystemId
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Constructor Details
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Block
public Block()Create an empty block
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Method Details
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makeBlock
Static factory method to create a block. If one of the arguments is already a block, the contents will be merged into a new composite block- Parameters:
e1
- the first subexpression (child) of the blocke2
- the second subexpression (child) of the block- Returns:
- a Block containing the two subexpressions, and if either of them is a block, it will have been collapsed to create a flattened sequence
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makeBlock
Static factory method to create a block from a list of expressions- Parameters:
list
- the list of expressions making up this block. The members of the List must be instances of Expression- Returns:
- a Block containing the two subexpressions, and if either of them is a block, it will have been collapsed to create a flattened sequence
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setChildren
Set the children of this instruction- Parameters:
children
- The instructions that are children of this instruction
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getExpressionName
Description copied from class:Instruction
Get a name identifying the kind of expression, in terms meaningful to a user.- Overrides:
getExpressionName
in classInstruction
- 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 explain() output displaying the expression.
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getChildren
Get the children of this instruction- Returns:
- the children of this instruction, as an array of Instruction objects. May return a zero-length array if there are no children
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computeSpecialProperties
public int computeSpecialProperties()Description copied from class:Instruction
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.- Overrides:
computeSpecialProperties
in classInstruction
- Returns:
- a set of flags indicating static properties of this expression
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mergeAdjacentTextInstructions
Merge any adjacent instructions that create literal text nodes- Returns:
- the expression after merging literal text instructions
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iterateSubExpressions
Description copied from class:Expression
Get the immediate sub-expressions of this expression. Default implementation returns a zero-length array, appropriate for an expression that has no sub-expressions.- Overrides:
iterateSubExpressions
in classExpression
- Returns:
- an iterator containing the sub-expressions of this expression
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replaceSubExpression
Replace one subexpression by a replacement subexpression- Overrides:
replaceSubExpression
in classExpression
- Parameters:
original
- the original subexpressionreplacement
- the replacement subexpression- Returns:
- true if the original subexpression is found
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copy
Copy an expression. This makes a deep copy.- Specified by:
copy
in classExpression
- Returns:
- the copy of the original expression
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getItemType
Determine the data type of the items returned by this expression- Overrides:
getItemType
in classInstruction
- Parameters:
th
- the type hierarchy cache- Returns:
- the data type
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getCardinality
public final int getCardinality()Determine the cardinality of the expression- Overrides:
getCardinality
in classExpression
- Returns:
- one of the values Cardinality.ONE_OR_MORE, Cardinality.ZERO_OR_MORE, Cardinality.EXACTLY_ONE, Cardinality.ZERO_OR_ONE, Cardinality.EMPTY. This default implementation returns ZERO_OR_MORE (which effectively gives no information).
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createsNewNodes
public final boolean createsNewNodes()Determine whether this instruction creates new nodes. This implementation returns true if any child instruction returns true.- Overrides:
createsNewNodes
in classInstruction
- Returns:
- true if the instruction creates new nodes (or if it can't be proved that it doesn't)
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checkForUpdatingSubexpressions
Check to ensure that this expression does not contain any updating subexpressions. This check is overridden for those expressions that permit updating subexpressions.- Overrides:
checkForUpdatingSubexpressions
in classExpression
- Throws:
XPathException
- if the expression has a non-permitted updateing subexpression
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isVacuousExpression
public boolean isVacuousExpression()Determine whether this is a vacuous expression as defined in the XQuery update specification- Overrides:
isVacuousExpression
in classExpression
- Returns:
- true if this expression is vacuous
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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 classInstruction
- Parameters:
visitor
- an expression visitor- Returns:
- the simplified expression
- Throws:
XPathException
- if an error is discovered during expression rewriting
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typeCheck
public Expression typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) throws XPathException Description copied from class: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 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.
- Overrides:
typeCheck
in classExpression
- Parameters:
visitor
- an expression visitorcontextItemType
- 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
- if an error is discovered during this phase (typically a type error)
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optimize
public Expression optimize(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType) throws XPathException Description copied from class: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.
- Overrides:
optimize
in classExpression
- Parameters:
visitor
- an expression visitorcontextItemType
- 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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promoteInst
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.- Overrides:
checkPermittedContents
in classExpression
- Parameters:
parentType
- the "given complex type": the method is checking that the nodes returned by this expression are acceptable members of the content model of this typeenv
- the static contextwhole
- if true, we want to check that the value of this expression satisfies the content model as a whole; if false we want to check that the value of the expression is acceptable as one part of the content- Throws:
XPathException
- if the value delivered by this expression cannot be part of the content model of the given type
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explain
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.- Specified by:
explain
in classExpression
- Parameters:
out
- the expression presenter used to display the structure
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processLeavingTail
Description copied from class:Instruction
ProcessLeavingTail: called to do the real work of this instruction. This method must be implemented in each subclass. The results of the instruction are written to the current Receiver, which can be obtained via the Controller.- Specified by:
processLeavingTail
in interfaceTailCallReturner
- Specified by:
processLeavingTail
in classInstruction
- Parameters:
context
- The dynamic context of the transformation, giving access to the current node, the current variables, etc.- Returns:
- null if the instruction has completed execution; or a TailCall indicating a function call or template call that is delegated to the caller, to be made after the stack has been unwound so as to save stack space.
- Throws:
XPathException
- if a dynamic error occurs during the evaluation of the instruction
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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. This implementation provides both iterate() and process() methods natively.- Overrides:
getImplementationMethod
in classInstruction
- Returns:
- the implementation method, for example
Expression.ITERATE_METHOD
orExpression.EVALUATE_METHOD
orExpression.PROCESS_METHOD
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iterate
Iterate over the results of all the child expressions- 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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iterateEvents
Get an EventIterator over the results of all the child expressions- Overrides:
iterateEvents
in classExpression
- Parameters:
context
- the XPath dynamic context- Returns:
- an EventIterator
- Throws:
XPathException
- if a dynamic error occurs during expression evaluation
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evaluatePendingUpdates
public void evaluatePendingUpdates(XPathContext context, PendingUpdateList pul) throws XPathException Evaluate an updating expression, adding the results to a Pending Update List. The default implementation of this method, which is used for non-updating expressions, throws an UnsupportedOperationException- Overrides:
evaluatePendingUpdates
in classExpression
- Parameters:
context
- the XPath dynamic evaluation contextpul
- the pending update list to which the results should be written- Throws:
XPathException
- if evaluation fails
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