net.sf.saxon.tree.iter
Class EmptyIterator<T extends Item>

java.lang.Object
  net.sf.saxon.tree.iter.EmptyIterator<T>

All Implemented Interfaces:

LastPositionFinder<T>, SequenceIterator<T>, GroundedIterator<T>, LookaheadIterator<T>, ReversibleIterator<T>, UnfailingIterator<T>

Direct Known Subclasses:

EmptyAxisIterator

public class EmptyIterator<T extends Item>
extends Object
implements SequenceIterator<T>, ReversibleIterator<T>, LastPositionFinder<T>, GroundedIterator<T>, LookaheadIterator<T>, UnfailingIterator<T>

EmptyIterator: an iterator over an empty sequence. Since such an iterator has no state, only one instance is required; therefore a singleton instance is available via the static getInstance() method.

Field Summary

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

GROUNDED, LAST_POSITION_FINDER, LOOKAHEAD

Constructor Summary

protected

EmptyIterator() Protected constructor

Method Summary

Value	atomize() Return the atomized value of the current node.
void	close() Close the iterator.
T	current() Get the current item, that is, the item returned by the most recent call of next().
static <T extends Item> EmptyIterator<T>	emptyIterator()
EmptyIterator<T>	getAnother() Get another iterator over the same items, positioned at the start.
static EmptyIterator	getInstance() Get an EmptyIterator, an iterator over an empty sequence.
int	getLength() Get the position of the last item in the sequence.
int	getProperties() Get properties of this iterator, as a bit-significant integer.
EmptyIterator<T>	getReverseIterator() Get another iterator over the same items, in reverse order.
CharSequence	getStringValue() Return the string value of the current node.
boolean	hasNext() Determine whether there are more items to come.
GroundedValue	materialize() Return a Value containing all the items in the sequence returned by this SequenceIterator.
T	next() Get the next item.
int	position() Get the position of the current item.

Methods inherited from class java.lang.Object

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

Constructor Detail

EmptyIterator

protected EmptyIterator()

Protected constructor

Method Detail

getInstance

public static EmptyIterator getInstance()

Get an EmptyIterator, an iterator over an empty sequence.

Returns:

an EmptyIterator (in practice, this always returns the same one)

emptyIterator

public static <T extends Item> EmptyIterator<T> emptyIterator()

next

public T next()

Get the next item.

Specified by:

next in interface SequenceIterator<T extends Item>

Specified by:

next in interface UnfailingIterator<T extends Item>

Returns:

the next item. For the EmptyIterator this is always null.

current

public T current()

Get the current item, that is, the item returned by the most recent call of next().

Specified by:

current in interface SequenceIterator<T extends Item>

Specified by:

current in interface UnfailingIterator<T extends Item>

Returns:

the current item. For the EmptyIterator this is always null.

position

public int position()

Get the position of the current item.

Specified by:

position in interface SequenceIterator<T extends Item>

Specified by:

position in interface UnfailingIterator<T extends Item>

Returns:

the position of the current item. For the EmptyIterator this is always zero (whether or not the next() method has been called).

getLength

public int getLength()

Get the position of the last item in the sequence.

Specified by:

getLength in interface LastPositionFinder<T extends Item>

Returns:

the position of the last item in the sequence, always zero in this implementation

close

public void close()

Description copied from interface: SequenceIterator

Close the iterator. This indicates to the supplier of the data that the client does not require any more items to be delivered by the iterator. This may enable the supplier to release resources. After calling close(), no further calls on the iterator should be made; if further calls are made, the effect of such calls is undefined.

(Currently, closing an iterator is important only when the data is being "pushed" in another thread. Closing the iterator terminates that thread and means that it needs to do no additional work. Indeed, failing to close the iterator may cause the push thread to hang waiting for the buffer to be emptied.)

Specified by:

close in interface SequenceIterator<T extends Item>

atomize

public Value atomize()

Return the atomized value of the current node.

Returns:

the atomized value.

Throws:

NullPointerException - always, because there is no current node

getStringValue

public CharSequence getStringValue()

Return the string value of the current node.

Returns:

the string value, as an instance of CharSequence.

Throws:

NullPointerException - if there is no current node

getAnother

public EmptyIterator<T> getAnother()

Get another iterator over the same items, positioned at the start.

Specified by:

getAnother in interface SequenceIterator<T extends Item>

Specified by:

getAnother in interface UnfailingIterator<T extends Item>

Returns:

another iterator over an empty sequence (in practice, it returns the same iterator each time)

getReverseIterator

public EmptyIterator<T> getReverseIterator()

Get another iterator over the same items, in reverse order.

Specified by:

getReverseIterator in interface ReversibleIterator<T extends Item>

Returns:

a reverse iterator over an empty sequence (in practice, it returns the same iterator each time)

getProperties

public int getProperties()

Get properties of this iterator, as a bit-significant integer.

Specified by:

getProperties in interface SequenceIterator<T extends Item>

Returns:

the properties of this iterator. This will be some combination of properties such as SequenceIterator.GROUNDED, SequenceIterator.LAST_POSITION_FINDER, and SequenceIterator.LOOKAHEAD. It is always acceptable to return the value zero, indicating that there are no known special properties. It is acceptable for the properties of the iterator to change depending on its state.

materialize

public GroundedValue materialize()

Return a Value containing all the items in the sequence returned by this SequenceIterator. This should be an "in-memory" value, not a Closure.

Specified by:

materialize in interface GroundedIterator<T extends Item>

Returns:

the corresponding Value

hasNext

public boolean hasNext()

Determine whether there are more items to come. Note that this operation is stateless and it is not necessary (or usual) to call it before calling next(). It is used only when there is an explicit need to tell if we are at the last element.

Specified by:

hasNext in interface LookaheadIterator<T extends Item>

Returns:

true if there are more nodes