net.sf.saxon.value
Class EmptySequence

java.lang.Object
  extended bynet.sf.saxon.value.Value
      extended bynet.sf.saxon.value.SequenceValue
          extended bynet.sf.saxon.value.EmptySequence
All Implemented Interfaces:
Expression, java.io.Serializable

public final class EmptySequence
extends SequenceValue

An EmptySequence object represents a sequence containing no members.

See Also:
Serialized Form

Method Summary
 void display(int level, NamePool pool)
          Diagnostic print of expression structure
 boolean effectiveBooleanValue(XPathContext context)
          Get the effective boolean value - always false
 boolean equals(java.lang.Object other)
          Is this expression the same as another expression?
 int getCardinality()
          Determine the static cardinality
static EmptySequence getInstance()
          Get the implicit instance of this class
 ItemType getItemType()
          Determine the item type
 int getSpecialProperties()
          Get the static properties of this expression (other than its type).
 int hashCode()
           
 SequenceIterator iterate(XPathContext context)
          Return an iteration over the sequence
 
Methods inherited from class net.sf.saxon.value.SequenceValue
conversionPreference, convertToJava, evaluateAsString, evaluateItem, itemAt, nodeToJavaPreference
 
Methods inherited from class net.sf.saxon.value.Value
analyze, asItem, asValue, collapseWhitespace, getDependencies, getSubExpressions, inverse, normalizeWhitespace, promote, simplify, stringToInteger, stringToNumber, trimWhitespace
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait
 

Method Detail

getInstance

public static EmptySequence getInstance()
Get the implicit instance of this class


iterate

public SequenceIterator iterate(XPathContext context)
                         throws XPathException
Return an iteration over the sequence

Parameters:
context - supplies the context for evaluation
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

getItemType

public ItemType getItemType()
Determine the item type

Specified by:
getItemType in interface Expression
Overrides:
getItemType in class SequenceValue
Returns:
AnyItemType (not known)

getCardinality

public int getCardinality()
Determine the static cardinality

Specified by:
getCardinality in interface Expression
Overrides:
getCardinality in class SequenceValue

getSpecialProperties

public int getSpecialProperties()
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.

Specified by:
getSpecialProperties in interface Expression
Overrides:
getSpecialProperties in class Value

equals

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

Throws:
java.lang.ClassCastException - if the values are not comparable

hashCode

public int hashCode()

effectiveBooleanValue

public boolean effectiveBooleanValue(XPathContext context)
Get the effective boolean value - always false

Specified by:
effectiveBooleanValue in interface Expression
Overrides:
effectiveBooleanValue in class SequenceValue
Parameters:
context - The context in which the expression is to be evaluated
Returns:
the effective boolean value

display

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

Specified by:
display in interface Expression
Overrides:
display in class SequenceValue