net.sf.saxon.value

Class EmptySequence

java.lang.Object

net.sf.saxon.value.EmptySequence

All Implemented Interfaces:

GroundedValue, Sequence

public final class EmptySequence
extends java.lang.Object
implements GroundedValue

An EmptySequence object represents a sequence containing no members.

Method Summary

Modifier and Type	Method and Description
Item	asItem() Return the value in the form of an Item
boolean	effectiveBooleanValue() Get the effective boolean value - always false
boolean	equals(java.lang.Object other) Is this expression the same as another expression?
static EmptySequence	getInstance() Get the implicit instance of this class
int	getLength() Get the length of the sequence
java.lang.String	getStringValue() Get the string value of this sequence.
java.lang.CharSequence	getStringValueCS() Get the string value of this sequence.
int	hashCode()
Item	head() Get the first item in the sequence.
Item	itemAt(int n) Get the n'th item in the sequence (starting from 0).
UnfailingIterator	iterate() Return an iteration over the sequence
GroundedValue	reduce() Reduce the sequence to its simplest form.
GroundedValue	subsequence(int min, int length) Get a subsequence of the value
java.lang.String	toString() Returns a string representation of the object.

Methods inherited from class java.lang.Object

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

Method Detail

getInstance

public static EmptySequence getInstance()

Get the implicit instance of this class

Returns:

the singular instances of this class: an empty sequence

getStringValue

public java.lang.String getStringValue()
                                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:

getStringValue 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)

getStringValueCS

public java.lang.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()

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

iterate

public UnfailingIterator iterate()

Return an iteration over the sequence

Specified by:

iterate in interface GroundedValue

Specified by:

iterate in interface Sequence

Returns:

an iterator over all the items

asItem

public Item asItem()

Return the value in the form of an Item

Returns:

the value in the form of an Item

getLength

public final int getLength()

Get the length of the sequence

Specified by:

getLength in interface GroundedValue

Returns:

always 0 for an empty sequence

equals

public boolean equals(java.lang.Object other)

Is this expression the same as another expression?

Overrides:

equals in class java.lang.Object

Throws:

java.lang.ClassCastException - if the values are not comparable

hashCode

public int hashCode()

Overrides:

hashCode in class java.lang.Object

effectiveBooleanValue

public boolean effectiveBooleanValue()

Get the effective boolean value - always false

Specified by:

effectiveBooleanValue in interface GroundedValue

Returns:

the effective boolean value

itemAt

public Item 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

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 min,
                                 int length)

Get a subsequence of the value

Specified by:

subsequence in interface GroundedValue

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 java.lang.String toString()

Returns a string representation of the object.

Overrides:

toString in class java.lang.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