net.sf.saxon.expr
Class SingleNodeExpression

java.lang.Object
  |
  +--net.sf.saxon.expr.ComputedExpression
        |
        +--net.sf.saxon.expr.SingleNodeExpression
All Implemented Interfaces:
Expression, java.io.Serializable
Direct Known Subclasses:
ParentNodeExpression, RootExpression

public abstract class SingleNodeExpression
extends ComputedExpression

A node set expression that will always return zero or one nodes

See Also:
Serialized Form

Field Summary
 
Fields inherited from class net.sf.saxon.expr.ComputedExpression
lineNumber, NO_ARGUMENTS, staticProperties
 
Constructor Summary
SingleNodeExpression()
           
 
Method Summary
 Expression analyze(StaticContext env)
          Type-check the expression.
 int computeCardinality()
          Specify that the expression returns a singleton
 boolean effectiveBooleanValue(XPathContext context)
          Get the effective boolean value of the expression.
 Item evaluateItem(XPathContext context)
          Evaluate an expression as a single item.
 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
abstract  NodeInfo getNode(XPathContext context)
          Get the single node to which this expression refers.
 SequenceIterator iterate(XPathContext context)
          Evaluate the expression in a given context to return an iterator
 
Methods inherited from class net.sf.saxon.expr.ComputedExpression
computeDependencies, computeSpecialProperties, computeStaticProperties, dynamicError, evaluateAsString, getCardinality, getDependencies, getLineNumber, getSourceLocator, getSpecialProperties, getSubExpressions, markTailFunctionCalls, promote, setLineNumber, simplify, typeError
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 
Methods inherited from interface net.sf.saxon.expr.Expression
display
 

Constructor Detail

SingleNodeExpression

public SingleNodeExpression()
Method Detail

analyze

public Expression analyze(StaticContext env)
                   throws XPathException
Type-check the expression.

Parameters:
env - the static context of the expression
Returns:
the original expression, rewritten to perform necessary run-time type checks, and to perform other type-related optimizations
XPathException

computeCardinality

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

Specified by:
computeCardinality in class ComputedExpression

getItemType

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

Returns:
Type.NODE

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

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

getNode

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

XPathException

iterate

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

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

evaluateItem

public Item evaluateItem(XPathContext context)
                  throws XPathException
Description copied from class: ComputedExpression
Evaluate an expression as a single item. This always returns either a single Item or null (denoting the empty sequence). No conversion is done. This method should not be used unless the static type of the expression is a subtype of "item" or "item?": that is, it should not be called if the expression may return a sequence. There is no guarantee that this condition will be detected.

Specified by:
evaluateItem in interface Expression
Overrides:
evaluateItem in class ComputedExpression
Parameters:
context - The context in which the expression is to be evaluated
Returns:
the node or atomic value that results from evaluating the expression; or null to indicate that the result is an empty sequence
Throws:
XPathException - if any dynamic error occurs evaluating the expression

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext context)
                              throws XPathException
Description copied from class: ComputedExpression
Get the effective boolean value of the expression. This returns false if the value is the empty sequence, a zero-length string, a number equal to zero, or the boolean false. Otherwise it returns true.

Specified by:
effectiveBooleanValue in interface Expression
Overrides:
effectiveBooleanValue in class ComputedExpression
Parameters:
context - The context in which the expression is to be evaluated
Returns:
the effective boolean value
Throws:
XPathException - if any dynamic error occurs evaluating the expression