net.sf.saxon.value
Class SingletonItem

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

All Implemented Interfaces:

Serializable, SequenceIterable, GroundedValue, ValueRepresentation

public class SingletonItem
extends Value
implements GroundedValue

A value that is a sequence containing zero or one items. Used only for items that are not atomic values (that is, nodes, and function items)

See Also:

Serialized Form

Field Summary

protected Item

item

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

INDETERMINATE_ORDERING

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

EMPTY_VALUE_ARRAY

Constructor Summary

SingletonItem(Item item)
Create a node-set containing zero or one nodes

Method Summary

Item	asItem() Return the value in the form of an Item
boolean	effectiveBooleanValue() Get the effective boolean value
int	getCardinality() Determine the static cardinality
Item	getItem() Get the node that forms the node-set.
ItemType	getItemType(TypeHierarchy th) Determine the data type of the items in the expression.
int	getLength() Get the length of the sequence
String	getStringValue() Convert the value to a string, using the serialization rules.
Item	itemAt(int n) Get the n'th item in the sequence (starting from 0).
SequenceIterator	iterate() Return an enumeration of this nodeset value.
void	process(XPathContext context) Process the instruction, without returning any tail calls
GroundedValue	subsequence(int start, int length) Get a subsequence of the value

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

asItem, asIterator, asValue, checkPermittedContents, convertToJava, equals, fromItem, getCanonicalLexicalRepresentation, getIterator, getSchemaComparable, getStringValueCS, hashCode, isIdentical, iterate, reduce

Methods inherited from class java.lang.Object

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

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

getStringValueCS

Field Detail

item

protected Item item

Constructor Detail

SingletonItem

public SingletonItem(Item item)

Create a node-set containing zero or one nodes

Parameters:

item - The node or function-item to be contained in the node-set, or null if the sequence is to be empty

Method Detail

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

process

public void process(XPathContext context)
             throws XPathException

Process the instruction, without returning any tail calls

Overrides:

process in class Value

Parameters:

context - The dynamic context, giving access to the current node, the current variables, etc.

Throws:

XPathException

getItemType

public ItemType getItemType(TypeHierarchy th)

Determine the data type of the items in the expression. This method determines the most precise type that it can, because it is called when testing that the node conforms to a required type.

Overrides:

getItemType in class Value

Parameters:

th - the type hierarchy cache

Returns:

the most precise possible type of the node.

getCardinality

public int getCardinality()

Determine the static cardinality

Overrides:

getCardinality in class Value

Returns:

the cardinality

getLength

public int getLength()
              throws XPathException

Get the length of the sequence

Overrides:

getLength in class Value

Returns:

the number of items in the sequence

Throws:

XPathException

itemAt

public Item itemAt(int n)

Get the n'th item in the sequence (starting from 0). This is defined for all SequenceValues, but its real benefits come for a SequenceValue 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 start,
                                 int length)

Get a subsequence of the value

Specified by:

subsequence in interface GroundedValue

Parameters:

start - 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

getItem

public Item getItem()

Get the node that forms the node-set. Return null if there is none.

iterate

public SequenceIterator iterate()

Return an enumeration of this nodeset value.

Specified by:

iterate in class Value

Returns:

an iterator over the sequence of items

effectiveBooleanValue

public boolean effectiveBooleanValue()

Get the effective boolean value

Overrides:

effectiveBooleanValue in class Value

Returns:

the effective boolean value

getStringValue

public String getStringValue()

Convert the value to a string, using the serialization rules. For atomic values this is the same as a cast; for sequence values it gives a space-separated list. For QNames and NOTATIONS, or lists containing them, it fails.

Specified by:

getStringValue in interface ValueRepresentation

Overrides:

getStringValue in class Value