net.sf.saxon.value
Class EmptySequence

java.lang.Object
  net.sf.saxon.value.Value
      net.sf.saxon.value.EmptySequence

All Implemented Interfaces:

Serializable, SequenceIterable, GroundedValue, ValueRepresentation

public final class EmptySequence
extends Value
implements GroundedValue

An EmptySequence object represents a sequence containing no members.

See Also:

Serialized Form

Field Summary

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

EMPTY_CLASS_ARRAY, INDETERMINATE_ORDERING

Fields inherited from interface net.sf.saxon.om.ValueRepresentation

EMPTY_VALUE_ARRAY

Method Summary

Item	asItem() Return the value in the form of an Item
boolean	effectiveBooleanValue() Get the effective boolean value - always false
boolean	equals(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(TypeHierarchy th) Determine the item type
int	getLength() Get the length of the sequence
int	hashCode()
Item	itemAt(int n) Get the n'th item in the sequence (starting from 0).
SequenceIterator	iterate() Return an iteration over the sequence
GroundedValue	subsequence(int min, int length) Get a subsequence of the value

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

asItem, asIterator, asValue, checkPermittedContents, convertJavaObjectToXPath, convertToJava, convertToJava, fromItem, getCanonicalLexicalRepresentation, getIterator, getSchemaComparable, getStringValue, getStringValueCS, iterate, makeQNameValue, process, reduce, stringToNumber, toString

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface net.sf.saxon.om.ValueRepresentation

getStringValue, getStringValueCS

Method Detail

getInstance

public static EmptySequence getInstance()

Get the implicit instance of this class

iterate

public SequenceIterator iterate()

Return an iteration over the sequence

Specified by:

iterate in class Value

Returns:

an iterator over the sequence of items

asItem

public Item asItem()

Return the value in the form of an Item

Overrides:

asItem in class Value

Returns:

the value in the form of an Item

getItemType

public ItemType getItemType(TypeHierarchy th)

Determine the item type

Overrides:

getItemType in class Value

Parameters:

th - the type hierarchy cache

Returns:

for the default implementation: AnyItemType (not known)

getCardinality

public int getCardinality()

Determine the static cardinality

Overrides:

getCardinality in class Value

Returns:

the cardinality

getLength

public final int getLength()

Get the length of the sequence

Overrides:

getLength in class Value

Returns:

always 0 for an empty sequence

equals

public boolean equals(Object other)

Is this expression the same as another expression?

Overrides:

equals in class Value

Throws:

ClassCastException - if the values are not comparable

hashCode

public int hashCode()

Overrides:

hashCode in class Object

effectiveBooleanValue

public boolean effectiveBooleanValue()

Get the effective boolean value - always false

Overrides:

effectiveBooleanValue in class Value

Returns:

the effective boolean value

itemAt

public Item itemAt(int n)

Get the n'th item in the sequence (starting from 0). This is defined for all Values, but its real benefits come for a sequence Value stored extensionally (or for a MemoClosure, once all the values have been read)

Specified by:

itemAt in interface GroundedValue

Overrides:

itemAt in class Value

Parameters:

n - position of the required item, counting from zero.

Returns:

the n'th item in the sequence, where the first item in the sequence is numbered zero. If n is negative or >= the length of the sequence, returns null.

subsequence

public GroundedValue subsequence(int min,
                                 int length)

Get a subsequence of the value

Specified by:

subsequence in interface GroundedValue

Parameters:

min - the index of the first item to be included in the result, counting from zero. A negative value is taken as zero. If the value is beyond the end of the sequence, an empty sequence is returned

length - the number of items to be included in the result. Specify Integer.MAX_VALUE to get the subsequence up to the end of the base sequence. If the value is negative, an empty sequence is returned. If the value goes off the end of the sequence, the result returns items up to the end of the sequence

Returns:

the required subsequence. If min is