net.sf.saxon.expr

Class AxisExpression

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.

Field Summary
intcomputedCardinality
Constructor Summary
AxisExpression(byte axis, NodeTest nodeTest)
Constructor
Method Summary
intcomputeCardinality()
Specify that the expression returns a singleton
intcomputeSpecialProperties()
Get the static properties of this expression (other than its type).
voiddisplay(int level, NamePool pool, PrintStream out)
Diagnostic print of expression structure
booleanequals(Object other)
Is this expression the same as another expression?
bytegetAxis()
Get the axis
intgetIntrinsicDependencies()
Determine which aspects of the context the expression depends on.
ItemTypegetItemType(TypeHierarchy th)
Determine the data type of the items returned by this expression
NodeTestgetNodeTest()
Get the NodeTest.
inthashCode()
get HashCode for comparing two expressions
SequenceIteratoriterate(XPathContext context)
Evaluate the path-expression in a given context to return a NodeSet
Expressionoptimize(Optimizer opt, StaticContext env, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
Expressionsimplify(StaticContext env)
Simplify an expression
StringtoString()
Represent the expression as a string for diagnostics
StringtoString(NamePool pool)
Represent the expression as a string for diagnostics
ExpressiontypeCheck(StaticContext env, ItemType contextItemType)
Type-check the expression

Field Detail

computedCardinality

int computedCardinality

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

computeCardinality

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

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.

display

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

equals

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

getAxis

public byte getAxis()
Get the axis

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

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

getNodeTest

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

hashCode

public int hashCode()
get HashCode for comparing two expressions

iterate

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

Parameters: context the evaluation context

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 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 ITEM_TYPE

Returns: the original expression, rewritten if appropriate to optimize execution

simplify

public Expression simplify(StaticContext env)
Simplify an expression

Returns: the simplified expression

toString

public String toString()
Represent the expression as a string for diagnostics

toString

public String toString(NamePool pool)
Represent the expression as a string for diagnostics

typeCheck

public Expression typeCheck(StaticContext env, ItemType contextItemType)
Type-check the expression