net.sf.saxon.expr

Class AxisExpression

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 call on reverse().

Field Summary
intcomputedCardinality
Constructor Summary
AxisExpression(byte axis, NodeTest nodeTest)
Constructor
Method Summary
PathMap.PathMapNodeSetaddToPathMap(PathMap pathMap, PathMap.PathMapNodeSet pathMapNodeSet)
Add a representation of this expression to a PathMap.
intcomputeCardinality()
Specify that the expression returns a singleton
intcomputeSpecialProperties()
Get the static properties of this expression (other than its type).
Expressioncopy()
Copy an expression.
booleanequals(Object other)
Is this expression the same as another expression?
voidexplain(ExpressionPresenter destination)
Diagnostic print of expression structure.
bytegetAxis()
Get the axis
ItemTypegetContextItemType()
Get the static type of the context item for this AxisExpression.
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
booleanisSubtreeExpression()
Determine whether the expression can be evaluated without reference to the part of the context document outside the subtree rooted at the context node.
SequenceIteratoriterate(XPathContext context)
Evaluate the path-expression in a given context to return a NodeSet
SequenceIteratoriterate(Item origin)
Iterate the axis from a given starting node, without regard to context
Expressionoptimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
Expressionsimplify(ExpressionVisitor visitor)
Simplify an expression
StringtoString()
Represent the expression as a string for diagnostics
StringtoString(NamePool pool)
Represent the expression as a string for diagnostics
ExpressiontypeCheck(ExpressionVisitor visitor, 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

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.

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

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.

copy

public Expression copy()
Copy an expression. This makes a deep copy.

Returns: the copy of the original expression

equals

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

explain

public void explain(ExpressionPresenter destination)
Diagnostic print of expression structure. The abstract expression tree is written to the supplied output destination.

getAxis

public byte getAxis()
Get the axis

Returns: the axis number, for example CHILD

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

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 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

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

hashCode

public int hashCode()
get HashCode for comparing two expressions

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.

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.

iterate

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

Parameters: context the evaluation context

iterate

public SequenceIterator iterate(Item origin)
Iterate the axis from a given starting node, without regard to context

Parameters: origin the starting node

Returns: the iterator over the axis

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.

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 ITEM_TYPE

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

simplify

public Expression simplify(ExpressionVisitor visitor)
Simplify an expression

Parameters: visitor an expression visitor

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

Parameters: pool the name pool, used for expanding names in the node test

Returns: a string representation of the expression

typeCheck

public Expression typeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Type-check the expression