Package net.sf.saxon.expr
Class AxisExpression
- java.lang.Object
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- net.sf.saxon.expr.Expression
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- net.sf.saxon.expr.AxisExpression
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- All Implemented Interfaces:
java.io.Serializable
,javax.xml.transform.SourceLocator
,LocationProvider
,SaxonLocator
,InstructionInfo
,org.xml.sax.Locator
public final class AxisExpression extends Expression
An AxisExpression is always obtained by simplifying a PathExpression. It represents a PathExpression that starts either at the context node or at some other singleton node, and uses a simple node-test with no filters. For example "*", "title", "./item", "@*", or "ancestor::chapter*".An AxisExpression delivers nodes in axis order (not in document order). To get nodes in document order, in the case of a reverse axis, the expression should be wrapped in a call on reverse().
Since 9.4, an axis expression does not necessarily select starting from the context item. This allows an expression such as $x/abcd (very common in XQuery FLWOR expressions) to be computed without creating a new context.
- See Also:
- Serialized Form
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Field Summary
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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 Constructor Description AxisExpression(byte axis, NodeTest nodeTest)
Constructor for an AxisExpression whose origin is the context item
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description PathMap.PathMapNodeSet
addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
Add a representation of this expression to a PathMap.int
computeCardinality()
Determine the cardinality of the result of this expressionint
computeSpecialProperties()
Get the static properties of this expression (other than its type).Expression
copy()
Copy an expression.boolean
equals(java.lang.Object other)
Is this expression the same as another expression?void
explain(ExpressionPresenter destination)
Diagnostic print of expression structure.byte
getAxis()
Get the axisItemType
getContextItemType()
Get the static type of the context item for this AxisExpression.java.lang.String
getExpressionName()
Get a name identifying the kind of expression, in terms meaningful to a user.int
getIntrinsicDependencies()
Determine the intrinsic dependencies of an expression, that is, those which are not derived from the dependencies of its subexpressions.ItemType
getItemType(TypeHierarchy th)
Determine the data type of the items returned by this expressionNodeTest
getNodeTest()
Get the NodeTest.int
hashCode()
get HashCode for comparing two expressionsboolean
isContextPossiblyUndefined()
Ask whether there is a possibility that the context item will be undefinedboolean
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.AxisIterator<? extends NodeInfo>
iterate(XPathContext context)
Evaluate the path-expression in a given context to return a NodeSetSequenceIterator
iterate(Item origin)
Iterate the axis from a given starting node, without regard to contextExpression
simplify(ExpressionVisitor visitor)
Simplify an expressionjava.lang.String
toString()
Represent the expression as a string for diagnosticsjava.lang.String
toString(NamePool pool)
Represent the expression as a string for diagnosticsExpression
typeCheck(ExpressionVisitor visitor, ExpressionVisitor.ContextItemType contextItemType)
Type-check the expression-
Methods inherited from class net.sf.saxon.expr.Expression
adoptChildExpression, checkForUpdatingSubexpressions, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, evaluatePendingUpdates, explain, getCardinality, getColumnNumber, getColumnNumber, getConstructType, getContainer, getDependencies, getEvaluationMethod, getExecutable, getHostLanguage, getImplementationMethod, getIntegerBounds, getLineNumber, getLineNumber, getLocationId, getLocationProvider, getObjectName, getProperties, getProperty, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, getSystemId, hasLoopingSubexpression, hasVariableBinding, implementsStaticTypeCheck, isUpdatingExpression, isVacuousExpression, iterateEvents, iterateSameFocusSubExpressions, iterateSubExpressions, markTailFunctionCalls, optimize, process, promote, replaceSubExpression, resetLocalStaticProperties, setContainer, setEvaluationMethod, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation, typeError
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Constructor Detail
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AxisExpression
public AxisExpression(byte axis, NodeTest nodeTest)
Constructor for an AxisExpression whose origin is the context item
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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:
getExpressionName
in 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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simplify
public Expression simplify(ExpressionVisitor visitor) throws XPathException
Simplify an expression- Overrides:
simplify
in classExpression
- 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
Type-check the expression- 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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getContextItemType
public ItemType getContextItemType()
Get the static type of the context item for this AxisExpression. May be null if not known.- Returns:
- the statically-inferred type, or null if not known
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equals
public boolean equals(java.lang.Object other)
Is this expression the same as another expression?- Overrides:
equals
in classjava.lang.Object
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hashCode
public int hashCode()
get HashCode for comparing two expressions- Overrides:
hashCode
in classjava.lang.Object
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copy
public Expression 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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computeSpecialProperties
public int computeSpecialProperties()
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 classExpression
- Returns:
- the special properties, as a bit-significant integer
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getItemType
public final ItemType getItemType(TypeHierarchy th)
Determine the data type of the items returned by this expression- Specified by:
getItemType
in classExpression
- Parameters:
th
- the type hierarchy cache- Returns:
- Type.NODE or a subtype, based on the NodeTest in the axis step, plus information about the content type if this is known from schema analysis
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getIntrinsicDependencies
public int getIntrinsicDependencies()
Determine 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:
getIntrinsicDependencies
in 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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computeCardinality
public final int computeCardinality()
Determine the cardinality of the result of this expression- Specified by:
computeCardinality
in 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
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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:
isSubtreeExpression
in 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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getAxis
public byte getAxis()
Get the axis- Returns:
- the axis number, for example
Axis.CHILD
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getNodeTest
public NodeTest getNodeTest()
Get the NodeTest. Returns null if the AxisExpression can return any node.- Returns:
- the node test, or null if all nodes are returned
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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.- Overrides:
addToPathMap
in classExpression
- Parameters:
pathMap
- the PathMap to which the expression should be addedpathMapNodeSet
-- Returns:
- the pathMapNode representing the focus established by this expression, in the case where this expression is the first operand of a path expression or filter expression
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isContextPossiblyUndefined
public boolean isContextPossiblyUndefined()
Ask whether there is a possibility that the context item will be undefined- Returns:
- true if this is a possibility
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iterate
public AxisIterator<? extends NodeInfo> iterate(XPathContext context) throws XPathException
Evaluate the path-expression in a given context to return a NodeSet- Overrides:
iterate
in classExpression
- Parameters:
context
- the evaluation context- 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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iterate
public SequenceIterator iterate(Item origin) throws XPathException
Iterate the axis from a given starting node, without regard to context- Parameters:
origin
- the starting node- Returns:
- the iterator over the axis
- Throws:
XPathException
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explain
public void explain(ExpressionPresenter destination)
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.- Specified by:
explain
in classExpression
- Parameters:
destination
- the expression presenter used to display the structure
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toString
public java.lang.String toString()
Represent the expression as a string for diagnostics- Overrides:
toString
in classExpression
- Returns:
- a representation of the expression as a string
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toString
public java.lang.String toString(NamePool pool)
Represent the expression as a string for diagnostics- Parameters:
pool
- the name pool, used for expanding names in the node test- Returns:
- a string representation of the expression
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