net.sf.saxon.om

Class ZeroOrOne<T extends Item>

java.lang.Object

net.sf.saxon.om.ZeroOrOne<T>

All Implemented Interfaces:

GroundedValue, Sequence

Direct Known Subclasses:

One

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

A value that is a sequence containing zero or one items.

Constructor Summary

Constructors

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

Method Summary

Methods

Modifier and Type	Method and Description
boolean	effectiveBooleanValue() Get the effective boolean value
static <T extends Item> ZeroOrOne<T>	empty() Return the instance of ZeroOrOne that represents the empty sequenec
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.
T	head() Get the first item in the sequence.
T	itemAt(int n) Get the n'th item in the sequence (starting from 0).
UnfailingIterator	iterate() Return an enumeration of this nodeset value.
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 (used only for diagnostics).

Methods inherited from class java.lang.Object

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

Constructor Detail

ZeroOrOne

public ZeroOrOne(T item)

Create a sequence containing zero or one items

Parameters:

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

Method Detail

empty

public static <T extends Item> ZeroOrOne<T> empty()

Return the instance of ZeroOrOne that represents the empty sequenec

Returns:

a representation of the empty sequence that satisfies the type ZeroOrOne

getStringValueCS

public CharSequence getStringValueCS()
                              throws XPathException

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)

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.

head

public T head()

Get the first item in the sequence.

Specified by:

head in interface GroundedValue

Specified by:

head in interface Sequence

Returns:

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

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 UnfailingIterator iterate()

Return an enumeration of this nodeset value.

Specified by:

iterate in interface GroundedValue

Specified by:

iterate in interface Sequence

Returns:

an iterator over all the items

effectiveBooleanValue

public boolean effectiveBooleanValue()
                              throws XPathException

Get the effective boolean value

Specified by:

effectiveBooleanValue in interface GroundedValue

Returns:

the effective boolean value

Throws:

XPathException - if the sequence has no effective boolean value (for example a sequence of two integers)

toString

public String toString()

Returns a string representation of the object (used only for diagnostics).

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