net.sf.saxon.value

Class SingletonItem<T extends Item>

java.lang.Object

net.sf.saxon.value.SingletonItem<T>

All Implemented Interfaces:

GroundedValue, Sequence

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

A value that is a sequence containing zero or one items. Used only for nodes.

Field Summary

Fields

Modifier and Type	Field and Description
protected T	item

Constructor Summary

Constructors

Constructor and Description
SingletonItem(T item) Create a sequence containing zero or one items

Method Summary

Methods

Modifier and Type	Method and Description
T	asItem() Return the value in the form of an Item
boolean	effectiveBooleanValue() Get the effective boolean value
int	getCardinality() Determine the static cardinality
int	getLength() Get the length of the sequence
String	getStringValue() Convert the value to a string, using the serialization rules.
CharSequence	getStringValueCS() Get the string value of this sequence.
Item	head() Get the first item in the sequence.
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	reduce() Reduce the sequence to its simplest form.
GroundedValue	subsequence(int start, int length) Get a subsequence of the value
String	toString() Returns a string representation of the object.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

item

protected T extends Item item

Constructor Detail

SingletonItem

public SingletonItem(T item)

Create a sequence containing zero or one items

Parameters:

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

Method Detail

getStringValueCS

public CharSequence getStringValueCS()
                              throws XPathException

Description copied from interface: GroundedValue

Get the string value of this sequence. The string value of an item is the result of applying the string() function. The string value of a sequence is the space-separated result of applying the string-join() function using a single space as the separator

Specified by:

getStringValueCS in interface GroundedValue

Returns:

the string value of the sequence.

Throws:

XPathException - if the sequence contains items that have no string value (for example, function items)

head

public Item head()
          throws XPathException

Get the first item in the sequence.

Specified by:

head in interface Sequence

Returns:

the first item in the sequence if there is one, or null if the sequence is empty

Throws:

XPathException - in the situation where the sequence is evaluated lazily, and evaluation of the first item causes a dynamic error.

asItem

public T asItem()

Return the value in the form of an 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

Parameters:

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

Throws:

XPathException

getCardinality

public int getCardinality()

Determine the static cardinality

getLength

public int getLength()

Get the length of the sequence

Specified by:

getLength in interface GroundedValue

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

Parameters:

n - the index of the required item, with 0 representing the first item in the sequence

Returns:

the n'th item if it exists, or null otherwise

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

iterate

public SequenceIterator<T> iterate()

Return an enumeration of this nodeset value.

Specified by:

iterate in interface Sequence

Returns:

an iterator over all the items

effectiveBooleanValue

public boolean effectiveBooleanValue()

Get the effective boolean value

Specified by:

effectiveBooleanValue in interface GroundedValue

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 GroundedValue

Returns:

the string value of the sequence.

toString

public String toString()

Returns a string representation of the object.

Overrides:

toString in class Object

Returns:

a string representation of the object.

reduce

public GroundedValue reduce()

Reduce the sequence to its simplest form. If the value is an empty sequence, the result will be EmptySequence.getInstance(). If the value is a single atomic value, the result will be an instance of AtomicValue. If the value is a single item of any other kind, the result will be an instance of SingletonItem. Otherwise, the result will typically be unchanged.

Specified by:

reduce in interface GroundedValue

Returns:

the simplified sequence