java.lang.Object
- net.sf.saxon.expr.Expression
- - net.sf.saxon.expr.AxisExpression

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

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

Constructor Summary

Constructors
Constructor Description

AxisExpression(byte axis, NodeTest nodeTest)
Constructor for an AxisExpression whose origin is the context item

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 expression
`int`	`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 axis
`ItemType`	`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 expression
`NodeTest`	`getNodeTest()`	Get the NodeTest.
`int`	`hashCode()`	get HashCode for comparing two expressions
`boolean`	`isContextPossiblyUndefined()`	Ask whether there is a possibility that the context item will be undefined
`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.
`AxisIterator<? extends NodeInfo>`	`iterate(XPathContext context)`	Evaluate the path-expression in a given context to return a NodeSet
`SequenceIterator`	`iterate(Item origin)`	Iterate the axis from a given starting node, without regard to context
`Expression`	`simplify(ExpressionVisitor visitor)`	Simplify an expression
`java.lang.String`	`toString()`	Represent the expression as a string for diagnostics
`java.lang.String`	`toString(NamePool pool)`	Represent the expression as a string for diagnostics
`Expression`	`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

Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait

- Constructor Detail
  - AxisExpression
```
public AxisExpression(byte axis,
                      NodeTest nodeTest)
```
    Constructor for an AxisExpression whose origin is the context item
    
    Parameters:
    
    axis - The axis to be used in this AxisExpression: relevant constants are defined in class 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
- Method Detail
  - getExpressionName
```
public java.lang.String getExpressionName()
```
    Get a name identifying the kind of expression, in terms meaningful to a user.
    
    Overrides:
    
    getExpressionName in class Expression
    
    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.
  - simplify
```
public Expression simplify(ExpressionVisitor visitor)
                    throws XPathException
```
    Simplify an expression
    
    Overrides:
    
    simplify in class Expression
    
    Parameters:
    
    visitor - an expression visitor
    
    Returns:
    
    the simplified expression
    
    Throws:
    
    XPathException - if an error is discovered during expression rewriting
  - typeCheck
```
public Expression typeCheck(ExpressionVisitor visitor,
                            ExpressionVisitor.ContextItemType contextItemType)
                     throws XPathException
```
    Type-check the expression
    
    Overrides:
    
    typeCheck in class Expression
    
    Parameters:
    
    visitor - an expression visitor
    
    contextItemType - 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 to Type.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)
  - 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
  - equals
```
public boolean equals(java.lang.Object other)
```
    Is this expression the same as another expression?
    
    Overrides:
    
    equals in class java.lang.Object
  - hashCode
```
public int hashCode()
```
    get HashCode for comparing two expressions
    
    Overrides:
    
    hashCode in class java.lang.Object
  - copy
```
public Expression copy()
```
    Copy an expression. This makes a deep copy.
    
    Specified by:
    
    copy in class Expression
    
    Returns:
    
    the copy of the original expression
  - 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 class Expression
    
    Returns:
    
    the special properties, as a bit-significant integer
  - getItemType
```
public final ItemType getItemType(TypeHierarchy th)
```
    Determine the data type of the items returned by this expression
    
    Specified by:
    
    getItemType in class Expression
    
    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
  - 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 class Expression
    
    Returns:
    
    a set of bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty
  - computeCardinality
```
public final int computeCardinality()
```
    Determine the cardinality of the result of this expression
    
    Specified by:
    
    computeCardinality in class Expression
    
    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
  - 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 class Expression
    
    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.
  - getAxis
```
public byte getAxis()
```
    Get the axis
    
    Returns:
    
    the axis number, for example Axis.CHILD
  - 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
  - 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 class Expression
    
    Parameters:
    
    pathMap - the PathMap to which the expression should be added
    
    pathMapNodeSet -
    
    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
  - isContextPossiblyUndefined
```
public boolean isContextPossiblyUndefined()
```
    Ask whether there is a possibility that the context item will be undefined
    
    Returns:
    
    true if this is a possibility
  - 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 class Expression
    
    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
  - 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
  - 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 class Expression
    
    Parameters:
    
    destination - the expression presenter used to display the structure
  - toString
```
public java.lang.String toString()
```
    Represent the expression as a string for diagnostics
    
    Overrides:
    
    toString in class Expression
    
    Returns:
    
    a representation of the expression as a string
  - 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

Class AxisExpression

Field Summary

Fields inherited from class net.sf.saxon.expr.Expression

Constructor Summary

Method Summary

Methods inherited from class net.sf.saxon.expr.Expression

Methods inherited from class java.lang.Object

Constructor Detail

AxisExpression

Method Detail

getExpressionName

simplify

typeCheck

getContextItemType

equals

hashCode

copy

computeSpecialProperties

getItemType

getIntrinsicDependencies

computeCardinality

isSubtreeExpression

getAxis

getNodeTest

addToPathMap

isContextPossiblyUndefined

iterate

iterate

explain

toString

toString