net.sf.saxon.value
Class EmptySequence<T extends Item>

java.lang.Object
  net.sf.saxon.value.Value<T>
      net.sf.saxon.value.EmptySequence<T>

All Implemented Interfaces:

GroundedValue<T>, ValueRepresentation<T>

public final class EmptySequence<T extends Item>
extends Value<T>
implements GroundedValue<T>

An EmptySequence object represents a sequence containing no members.

Field Summary

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

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 <T extends Item> EmptySequence<T>	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()
T	itemAt(int n) Get the n'th item in the sequence (starting from 0).
SequenceIterator<T>	iterate() Return an iteration over the sequence
GroundedValue<T>	subsequence(int min, int length) Get a subsequence of the value
String	toString() Returns a string representation of the object.

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

asItem, asIterator, asValue, checkPermittedContents, convertToJava, fromItem, getCanonicalLexicalRepresentation, getIterator, getSchemaComparable, getSequenceLength, getStringValue, getStringValueCS, isIdentical, process, reduce

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

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

getStringValue, getStringValueCS

Method Detail

getInstance

public static <T extends Item> EmptySequence<T> getInstance()

Get the implicit instance of this class

Returns:

the singular instances of this class: an empty sequence

iterate

public SequenceIterator<T> iterate()

Return an iteration over the sequence

Specified by:

iterate in class Value<T extends Item>

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<T extends Item>

Returns:

the value in the form of an Item

getItemType

public ItemType getItemType(TypeHierarchy th)

Determine the item type

Overrides:

getItemType in class Value<T extends Item>

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<T extends Item>

Returns:

the cardinality

getLength

public final int getLength()

Get the length of the sequence

Specified by:

getLength in interface GroundedValue<T extends Item>

Overrides:

getLength in class Value<T extends Item>

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<T extends Item>

Throws:

ClassCastException - if the values are not comparable

hashCode

public int hashCode()

Overrides:

hashCode in class Value<T extends Item>

effectiveBooleanValue

public boolean effectiveBooleanValue()

Get the effective boolean value - always false

Overrides:

effectiveBooleanValue in class Value<T extends Item>

Returns:

the effective boolean value

itemAt

public T 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<T extends Item>

Overrides:

itemAt in class Value<T extends Item>

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<T> subsequence(int min,
                                    int length)

Get a subsequence of the value

Specified by:

subsequence in interface GroundedValue<T extends Item>

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

toString

public String toString()

Returns a string representation of the object.

Overrides:

toString in class Object