Package net.sf.saxon.expr
Class AxisExpression
- java.lang.Object
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- net.sf.saxon.expr.ComputedExpression
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- net.sf.saxon.expr.AxisExpression
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- All Implemented Interfaces:
java.io.Serializable
,javax.xml.transform.SourceLocator
,Container
,Expression
,InstructionInfoProvider
public final class AxisExpression extends ComputedExpression
An AxisExpression is always obtained by simplifying a PathExpression. It represents a PathExpression that starts at the context 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 Reverser.
- See Also:
- Serialized Form
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Field Summary
Fields Modifier and Type Field Description (package private) int
computedCardinality
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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 AxisExpression(byte axis, NodeTest nodeTest)
Constructor
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description int
computeCardinality()
Specify that the expression returns a singletonint
computeSpecialProperties()
Get the static properties of this expression (other than its type).void
display(int level, java.io.PrintStream out, Configuration config)
Diagnostic print of expression structureboolean
equals(java.lang.Object other)
Is this expression the same as another expression?byte
getAxis()
Get the axisItemType
getContextItemType()
Get the static type of the context item for this AxisExpression.int
getIntrinsicDependencies()
Determine which aspects of the context the expression depends on.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 expressionsSequenceIterator
iterate(XPathContext context)
Evaluate the path-expression in a given context to return a NodeSetExpression
optimize(Optimizer opt, StaticContext env, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.Expression
simplify(StaticContext env)
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(StaticContext env, ItemType contextItemType)
Type-check the expression-
Methods inherited from class net.sf.saxon.expr.ComputedExpression
adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, doPromotion, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getLineNumber, getLocationId, getLocationProvider, getParentExpression, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasBadParentPointer, iterateSubExpressions, markTailFunctionCalls, process, promote, replaceSubExpression, resetStaticProperties, setLocationId, setParentExpression, setParentExpression, suppressValidation, typeError
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Constructor Detail
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AxisExpression
public AxisExpression(byte axis, NodeTest nodeTest)
Constructor- Parameters:
axis
- The axis to be used in this AxisExpression: relevant constants are defined in class net.sf.saxon.om.Axis.nodeTest
- The conditions to be satisfied by selected nodes. May be null, indicating that any node on the axis is acceptable- See Also:
Axis
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Method Detail
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simplify
public Expression simplify(StaticContext env)
Simplify an expression- Specified by:
simplify
in interfaceExpression
- Overrides:
simplify
in classComputedExpression
- Parameters:
env
- the static context- Returns:
- the simplified expression
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typeCheck
public Expression typeCheck(StaticContext env, ItemType contextItemType) throws XPathException
Type-check the expression- 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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getContextItemType
public ItemType getContextItemType()
Get the static type of the context item for this AxisExpression. May be null if not known.
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optimize
public Expression optimize(Optimizer opt, StaticContext env, ItemType contextItemType)
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.
- 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
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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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getIntrinsicDependencies
public int getIntrinsicDependencies()
Determine which aspects of the context the expression depends on. The result is a bitwise-or'ed value composed from constants such as XPathContext.VARIABLES and XPathContext.CURRENT_NODE- Overrides:
getIntrinsicDependencies
in classComputedExpression
- 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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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 classComputedExpression
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getItemType
public final ItemType getItemType(TypeHierarchy th)
Determine the data type of the items returned by this expression- Parameters:
th
-- 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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computeCardinality
public final int computeCardinality()
Specify that the expression returns a singleton- Specified by:
computeCardinality
in classComputedExpression
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getAxis
public byte getAxis()
Get the axis
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getNodeTest
public NodeTest getNodeTest()
Get the NodeTest. Returns null if the AxisExpression can return any node.
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iterate
public SequenceIterator iterate(XPathContext context) throws XPathException
Evaluate the path-expression in a given context to return a NodeSet- Specified by:
iterate
in interfaceExpression
- Overrides:
iterate
in classComputedExpression
- 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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display
public void display(int level, java.io.PrintStream out, Configuration config)
Diagnostic print of expression structure- Parameters:
level
- indentation level for this expressionout
- Output destination
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toString
public java.lang.String toString()
Represent the expression as a string for diagnostics- Overrides:
toString
in classjava.lang.Object
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toString
public java.lang.String toString(NamePool pool)
Represent the expression as a string for diagnostics
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