net.sf.saxon.expr
Class AxisExpression

java.lang.Object
  extended by net.sf.saxon.expr.Expression
      extended by net.sf.saxon.expr.AxisExpression
All Implemented Interfaces:
Serializable, SourceLocator, EvaluableItem, SequenceIterable, InstructionInfoProvider

public final class AxisExpression
extends Expression

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

Field Summary
 
Fields inherited from class net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
 
Constructor Summary
AxisExpression(byte axis, NodeTest nodeTest)
          Constructor
 
Method Summary
 PathMap.PathMapNodeSet addToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
          Add a representation of this expression to a PathMap.
 int computeCardinality()
          Specify that the expression returns a singleton
 int computeSpecialProperties()
          Get the static properties of this expression (other than its type).
 Expression copy()
          Copy an expression.
 boolean equals(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.
 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 expression
 NodeTest getNodeTest()
          Get the NodeTest.
 int hashCode()
          get HashCode for comparing two expressions
 SequenceIterator iterate(Item origin)
          Iterate the axis from a given starting node, without regard to context
 SequenceIterator iterate(XPathContext context)
          Evaluate the path-expression in a given context to return a NodeSet
 Expression optimize(ExpressionVisitor visitor, ItemType contextItemType)
          Perform optimisation of an expression and its subexpressions.
 Expression simplify(ExpressionVisitor visitor)
          Simplify an expression
 String toString()
          Represent the expression as a string for diagnostics
 String toString(NamePool pool)
          Represent the expression as a string for diagnostics
 Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
          Type-check the expression
 
Methods inherited from class net.sf.saxon.expr.Expression
adoptChildExpression, checkPermittedContents, computeDependencies, computeStaticProperties, display, doPromotion, effectiveBooleanValue, evaluateAsString, evaluateItem, explain, findParentOf, getCardinality, getColumnNumber, getContainer, getDependencies, getExecutable, getHostLanguage, getImplementationMethod, getInstructionInfo, getLineNumber, getLocationId, getLocationProvider, getPublicId, getSlotsUsed, getSpecialProperties, getSystemId, hasLoopingSubexpression, implementsStaticTypeCheck, iterateEvents, iterateSubExpressions, markTailFunctionCalls, process, promote, replaceSubExpression, setContainer, setFiltered, setFlattened, setLocationId, staticTypeCheck, suppressValidation
 
Methods inherited from class java.lang.Object
getClass, notify, notifyAll, wait, wait, wait
 

Constructor Detail

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
Method Detail

simplify

public Expression simplify(ExpressionVisitor visitor)
Simplify an expression

Overrides:
simplify in class Expression
Parameters:
visitor - an expression visitor
Returns:
the simplified expression

typeCheck

public Expression typeCheck(ExpressionVisitor visitor,
                            ItemType 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

optimize

public Expression optimize(ExpressionVisitor visitor,
                           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.

Overrides:
optimize 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 if appropriate to optimize execution

equals

public boolean equals(Object other)
Is this expression the same as another expression?

Overrides:
equals in class Object

hashCode

public int hashCode()
get HashCode for comparing two expressions

Overrides:
hashCode in class Object

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 class Expression
Returns:
a set of bit-significant flags identifying the "intrinsic" dependencies. The flags are documented in class net.sf.saxon.value.StaticProperty

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.

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

computeCardinality

public final int computeCardinality()
Specify that the expression returns a singleton

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

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

iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException
Evaluate the path-expression in a given context to return a NodeSet

Specified by:
iterate in interface SequenceIterable
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 String toString()
Represent the expression as a string for diagnostics

Overrides:
toString in class Expression

toString

public 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


Copyright (C) Michael H. Kay. All rights reserved.