net.sf.saxon.value
Class EmptySequence

java.lang.Object
  |
  +--net.sf.saxon.value.Value
        |
        +--net.sf.saxon.value.SequenceValue
              |
              +--net.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, getStringValue, itemAt, nodeToJavaPreference

 

Methods inherited from class net.sf.saxon.value.Value

analyze, asItem, asValue, collapseWhitespace, getDependencies, getSubExpressions, inverse, normalizeWhitespace, promote, simplify, 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

Returns:

one of the values Cardinality.ONE_OR_MORE, Cardinality.ZERO_OR_MORE, Cardinality.EXACTLY_ONE, Cardinality.ZERO_OR_ONE, Cardinality.EMPTY. This default implementation returns ZERO_OR_MORE (which effectively gives no information).

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

Returns:

zero

equals

public boolean equals(java.lang.Object other)

Is this expression the same as another expression?

Overrides:

equals in class java.lang.Object

Throws:

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

hashCode

public int hashCode()

Overrides:

hashCode in class java.lang.Object

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

Parameters:

level - indentation level for this expression