Class ContextItemExpression
- java.lang.Object
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- net.sf.saxon.expr.Expression
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- net.sf.saxon.expr.ContextItemExpression
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- All Implemented Interfaces:
ExportAgent,Locatable,IdentityComparable,Traceable
- Direct Known Subclasses:
CurrentItemExpression
public class ContextItemExpression extends Expression
This class represents the expression "(dot)", which always returns the context item. This may be a AtomicValue or a Node.
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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 ContextItemExpression()Create the expression
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description PathMap.PathMapNodeSetaddToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)Add a representation of this expression to a PathMap.intcomputeCardinality()Get the static cardinalityintcomputeHashCode()get HashCode for comparing two expressionsintcomputeSpecialProperties()Determine the special properties of this expressionExpressioncopy(RebindingMap rebindings)Create a clone copy of this expressionbooleanequals(java.lang.Object other)Is this expression the same as another expression?ItemevaluateItem(XPathContext context)Evaluate the expressionvoidexport(ExpressionPresenter destination)Diagnostic print of expression structure.java.lang.StringgetErrorCodeForUndefinedContext()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().intgetIntrinsicDependencies()Determine the intrinsic dependencies of an expression, that is, those which are not derived from the dependencies of its subexpressions.ItemTypegetItemType()Determine the item typeintgetNetCost()Return the net cost of evaluating this expression, excluding the cost of evaluating its operands.UTypegetStaticUType(UType contextItemType)Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.java.lang.StringgetStreamerName()Get the (partial) name of a class that supports streaming of this kind of expressionbooleanisContextPossiblyUndefined()Ask whether the context item may possibly be undefinedbooleanisSubtreeExpression()Determine whether the expression can be evaluated without reference to the part of the context document outside the subtree rooted at the context node.SequenceIteratoriterate(XPathContext context)Iterate over the value of the expressionExpressionoptimize(ExpressionVisitor visitor, ContextItemStaticInfo contextItemType)Perform optimisation of an expression and its subexpressions.voidsetErrorCodeForUndefinedContext(java.lang.String errorCode, boolean isTypeError)voidsetStaticInfo(ContextItemStaticInfo info)Set static information about the context itemPatterntoPattern(Configuration config)Convert this expression to an equivalent XSLT patternjava.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, but there is no guarantee that the syntax will actually be true XPath.ExpressiontypeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo)Type-check the expression.-
Methods inherited from class net.sf.saxon.expr.Expression
adoptChildExpression, allowExtractingCommonSubexpressions, checkedOperands, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, dynamicError, effectiveBooleanValue, evaluateAsString, evaluatePendingUpdates, explain, getCardinality, getConfiguration, getCost, getDependencies, getEvaluationMethod, getExtraProperty, getIntegerBounds, getInterpretedExpression, getLocalRetainedStaticContext, getLocation, getObjectName, getPackageData, getParentExpression, getProperties, getProperty, getRetainedStaticContext, getScopingExpression, getSlotsUsed, getSpecialProperties, getStaticBaseURI, getStaticBaseURIString, getStaticType, getTracingTag, hasCompatibleStaticContext, hashCode, hasSpecialProperty, hasVariableBinding, identityHashCode, implementsStaticTypeCheck, isCallOn, isEqual, isIdentical, isInstruction, isLiftable, isMultiThreaded, isStaticPropertiesKnown, isUpdatingExpression, isVacuousExpression, markTailFunctionCalls, operandList, operands, operandSparseList, optimizeChildren, prepareForStreaming, process, resetLocalStaticProperties, restoreParentPointers, setEvaluationMethod, setExtraProperty, setFiltered, setFlattened, setLocation, setParentExpression, setRetainedStaticContext, setRetainedStaticContextLocally, setRetainedStaticContextThoroughly, setStaticProperty, simplify, simplifyChildren, staticTypeCheck, suppressValidation, 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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Method Detail
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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 explain() output displaying the expression.
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copy
public Expression copy(RebindingMap rebindings)
Create a clone copy of this expression- Specified by:
copyin classExpression- Parameters:
rebindings-- Returns:
- a copy of this expression
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setErrorCodeForUndefinedContext
public void setErrorCodeForUndefinedContext(java.lang.String errorCode, boolean isTypeError)
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getErrorCodeForUndefinedContext
public java.lang.String getErrorCodeForUndefinedContext()
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setStaticInfo
public void setStaticInfo(ContextItemStaticInfo info)
Set static information about the context item- Parameters:
info- static information about the context item
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typeCheck
public Expression typeCheck(ExpressionVisitor visitor, ContextItemStaticInfo contextInfo) throws XPathException
Type-check the expression.- Overrides:
typeCheckin classExpression- Parameters:
visitor- an expression visitorcontextInfo- Information available statically about the context item: whether it is (possibly) absent; its static type; its streaming posture.- 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, ContextItemStaticInfo contextItemType) throws XPathException
Perform 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 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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getItemType
public ItemType getItemType()
Determine the item type- Specified by:
getItemTypein classExpression- 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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getStaticUType
public UType getStaticUType(UType contextItemType)
Get the static type of the expression as a UType, following precisely the type inference rules defined in the XSLT 3.0 specification.- Overrides:
getStaticUTypein classExpression- Parameters:
contextItemType- the static type of the context item- Returns:
- the static item type of the expression according to the XSLT 3.0 defined rules
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isContextPossiblyUndefined
public boolean isContextPossiblyUndefined()
Ask whether the context item may possibly be undefined- Returns:
- true if it might be undefined
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computeCardinality
public int computeCardinality()
Get the static cardinality- Specified by:
computeCardinalityin classExpression- 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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computeSpecialProperties
public int computeSpecialProperties()
Determine the special properties of this expression- Overrides:
computeSpecialPropertiesin classExpression- Returns:
- the value
StaticProperty.NO_NODES_NEWLY_CREATED
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getImplementationMethod
public int getImplementationMethod()
Description copied from class:ExpressionAn 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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equals
public boolean equals(java.lang.Object other)
Is this expression the same as another expression?- Overrides:
equalsin classExpression- Parameters:
other- the other operand; the result is false if this is not an Expression- Returns:
- true if the other operand is an expression and if it can be determined that the two expressions are equivalent, in the sense that they will always return the same result.
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computeHashCode
public int computeHashCode()
get HashCode for comparing two expressions- Overrides:
computeHashCodein classExpression- Returns:
- a computed hash code
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getIntrinsicDependencies
public int getIntrinsicDependencies()
Description copied from class:ExpressionDetermine the intrinsic dependencies of an expression, that is, those which are not derived from the dependencies of its subexpressions. For example, position() has an intrinsic dependency on the context position, while (position()+1) does not. The default implementation of the method returns 0, indicating "no dependencies".- Overrides:
getIntrinsicDependenciesin classExpression- Returns:
- a set of bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty
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addToPathMap
public PathMap.PathMapNodeSet addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
Add a representation of this expression to a PathMap. The PathMap captures a map of the nodes visited by an expression in a source tree.The default implementation of this method assumes that an expression does no navigation other than the navigation done by evaluating its subexpressions, and that the subexpressions are evaluated in the same context as the containing expression. The method must be overridden for any expression where these assumptions do not hold. For example, implementations exist for AxisExpression, ParentExpression, and RootExpression (because they perform navigation), and for the doc(), document(), and collection() functions because they create a new navigation root. Implementations also exist for PathExpression and FilterExpression because they have subexpressions that are evaluated in a different context from the calling expression.
- Overrides:
addToPathMapin classExpression- Parameters:
pathMap- the PathMap to which the expression should be addedpathMapNodeSet- the PathMapNodeSet to which the paths embodied in this expression should be added- Returns:
- the pathMapNodeSet representing the points in the source document that are both reachable by this expression, and that represent possible results of this expression. For an expression that does navigation, it represents the end of the arc in the path map that describes the navigation route. For other expressions, it is the same as the input pathMapNode.
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isSubtreeExpression
public boolean isSubtreeExpression()
Determine whether the expression can be evaluated without reference to the part of the context document outside the subtree rooted at the context node.- Overrides:
isSubtreeExpressionin classExpression- Returns:
- true if the expression has no dependencies on the context node, or if the only dependencies on the context node are downward selections using the self, child, descendant, attribute, and namespace axes.
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getNetCost
public int getNetCost()
Description copied from class:ExpressionReturn the net cost of evaluating this expression, excluding the cost of evaluating its operands. We take the cost of evaluating a simple scalar comparison or arithmetic expression as 1 (one).- Overrides:
getNetCostin classExpression- Returns:
- the intrinsic cost of this operation, excluding the costs of evaluating the operands
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toPattern
public Pattern toPattern(Configuration config) throws XPathException
Convert this expression to an equivalent XSLT pattern- Overrides:
toPatternin classExpression- Parameters:
config- the Saxon configuration- Returns:
- the equivalent pattern
- Throws:
XPathException- if conversion is not possible
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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
Iterate over the value of the expression- 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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evaluateItem
public Item evaluateItem(XPathContext context) throws XPathException
Evaluate the expression- Overrides:
evaluateItemin classExpression- 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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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, but there is no guarantee that the syntax will actually be true XPath. In the case of XSLT instructions, the toString() method gives an abstracted view of the syntax- Overrides:
toStringin classExpression- Returns:
- a representation of the expression as a string
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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- Specified by:
exportin classExpression- 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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toShortString
public java.lang.String toShortString()
Description copied from class:ExpressionProduce a short string identifying the expression for use in error messages- Overrides:
toShortStringin classExpression- Returns:
- a short string, sufficient to identify the expression
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