net.sf.saxon.expr

Class SingleNodeExpression

public abstract class SingleNodeExpression extends Expression

A node set expression that will always return zero or one nodes
Method Summary
intcomputeCardinality()
Specify that the expression returns a singleton
intcomputeSpecialProperties()
booleaneffectiveBooleanValue(XPathContext context)
ItemevaluateItem(XPathContext context)
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
abstract NodeInfogetNode(XPathContext context)
Get the single node to which this expression refers.
SequenceIteratoriterate(XPathContext context)
Evaluate the expression in a given context to return an iterator
protected abstract StringnoContextMessage()
Customize the error message on type checking
Expressionoptimize(ExpressionVisitor visitor, ItemType contextItemType)
Perform optimisation of an expression and its subexpressions.
ExpressiontypeCheck(ExpressionVisitor visitor, ItemType contextItemType)
Type-check the expression.

Method Detail

computeCardinality

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

computeSpecialProperties

public int computeSpecialProperties()

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext context)

evaluateItem

public Item evaluateItem(XPathContext context)

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 StaticProperty.VARIABLES and StaticProperty.CURRENT_NODE

getItemType

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

Parameters: th the type hierarchy cache

Returns: Type.NODE

getNode

public abstract NodeInfo getNode(XPathContext context)
Get the single node to which this expression refers. Returns null if the node-set is empty

iterate

public SequenceIterator iterate(XPathContext context)
Evaluate the expression in a given context to return an iterator

Parameters: context the evaluation context

noContextMessage

protected abstract String noContextMessage()
Customize the error message on type checking

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

Throws: XPathException if an error is discovered during this phase (typically a type error)

typeCheck

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