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

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

All Implemented Interfaces:

GroundedValue<T>, ValueRepresentation<T>

public class SingletonItem<T extends Item>
extends Value<T>
implements GroundedValue<T>

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)

Field Summary

protected T

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

Method Summary

T	asItem() Return the value in the form of an Item
boolean	effectiveBooleanValue() Get the effective boolean value
int	getCardinality() Determine the static cardinality
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.
T	itemAt(int n) Get the n'th item in the sequence (starting from 0).
SequenceIterator<T>	iterate() Return an enumeration of this nodeset value.
void	process(XPathContext context) Process the instruction, without returning any tail calls
GroundedValue<T>	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, getSequenceLength, getStringValueCS, hashCode, isIdentical, 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 T extends Item item

Constructor Detail

SingletonItem

public SingletonItem(T 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 T 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

process

public void process(XPathContext context)
             throws XPathException

Process the instruction, without returning any tail calls

Overrides:

process in class Value<T extends Item>

Parameters:

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

Throws:

XPathException - if an error occurs (for example if the value is a closure that needs to be evaluated)

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<T extends Item>

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<T extends Item>

Returns:

the cardinality

getLength

public 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:

the number of items in the sequence

itemAt

public T 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<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 start,
                                    int length)

Get a subsequence of the value

Specified by:

subsequence in interface GroundedValue<T extends Item>

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

iterate

public SequenceIterator<T> iterate()

Return an enumeration of this nodeset value.

Specified by:

iterate in class Value<T extends Item>

Returns:

an iterator over the sequence of items

effectiveBooleanValue

public boolean effectiveBooleanValue()

Get the effective boolean value

Overrides:

effectiveBooleanValue in class Value<T extends Item>

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<T extends Item>

Overrides:

getStringValue in class Value<T extends Item>

Returns:

the result of converting the value to a string