net.sf.saxon.expr
Class AxisExpression

java.lang.Object
  |
  +--net.sf.saxon.expr.ComputedExpression
        |
        +--net.sf.saxon.expr.AxisExpression
All Implemented Interfaces:
Container, Expression, InstructionInfoProvider, java.io.Serializable, javax.xml.transform.SourceLocator

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

Field Summary
 
Fields inherited from class net.sf.saxon.expr.ComputedExpression
locationId, staticProperties
 
Fields inherited from interface net.sf.saxon.expr.Expression
EVALUATE_METHOD, ITERATE_METHOD, PROCESS_METHOD
 
Constructor Summary
AxisExpression(byte axis, NodeTest nodeTest)
          Constructor
 
Method Summary
 Expression analyze(StaticContext env, ItemType contextItemType)
          Type-check the expression
 int computeCardinality()
          Specify that the expression returns a singleton
 int computeSpecialProperties()
          Get the static properties of this expression (other than its type).
 void display(int level, NamePool pool, java.io.PrintStream out)
          Diagnostic print of expression structure
 boolean equals(java.lang.Object other)
          Is this expression the same as another expression?
 byte getAxis()
          Get the axis
 int getIntrinsicDependencies()
          Determine which aspects of the context the expression depends on.
 ItemType getItemType()
          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(XPathContext context)
          Evaluate the path-expression in a given context to return a NodeSet
 Expression simplify(StaticContext env)
          Simplify an expression
 
Methods inherited from class net.sf.saxon.expr.ComputedExpression
adoptChildExpression, computeDependencies, computeStaticProperties, dynamicError, dynamicError, effectiveBooleanValue, evaluateAsString, evaluateItem, getCardinality, getColumnNumber, getConstructType, getDependencies, getExecutable, getImplementationMethod, getInstructionInfo, getLineNumber, getLocationId, getParentExpression, getPublicId, getSpecialProperties, getSystemId, iterateSubExpressions, markTailFunctionCalls, process, promote, resetStaticProperties, setLocationId, setParentExpression, typeError
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, toString, 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(StaticContext env)
Simplify an expression

Specified by:
simplify in interface Expression
Overrides:
simplify in class ComputedExpression
Returns:
the simplified expression

analyze

public Expression analyze(StaticContext env,
                          ItemType contextItemType)
                   throws XPathException
Type-check the expression

Parameters:
env - the static context of the expression
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
XPathException

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

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

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 ComputedExpression

getItemType

public final ItemType getItemType()
Determine the data type of the items returned by this expression

Returns:
Type.NODE or a subtype, based on the NodeTest in the axis step

computeCardinality

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

Specified by:
computeCardinality in class ComputedExpression

getAxis

public byte getAxis()
Get the axis


getNodeTest

public NodeTest getNodeTest()
Get the NodeTest. Returns null if the AxisExpression can return any node.


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 Expression
Overrides:
iterate in class ComputedExpression
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

display

public void display(int level,
                    NamePool pool,
                    java.io.PrintStream out)
Diagnostic print of expression structure

Parameters:
level - indentation level for this expression
pool - NamePool used to expand any names appearing in the expression
out - Output destination