net.sf.saxon.tree.iter
Class EmptyIterator

java.lang.Object
  net.sf.saxon.tree.iter.EmptyIterator

All Implemented Interfaces:

LastPositionFinder, SequenceIterator, AxisIterator, GroundedIterator, LookaheadIterator, ReversibleIterator, UnfailingIterator

public class EmptyIterator
extends Object
implements AxisIterator, ReversibleIterator, LastPositionFinder, GroundedIterator, LookaheadIterator

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

Method Summary

Value	atomize() Return the atomized value of the current node.
void	close() Close the iterator.
Item	current() Get the current item, that is, the item returned by the most recent call of next().
SequenceIterator	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	getLastPosition() Get the position of the last item in the sequence.
int	getProperties() Get properties of this iterator, as a bit-significant integer.
SequenceIterator	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.
AxisIterator	iterateAxis(byte axis, NodeTest test) Return an iterator over an axis, starting at the current node.
GroundedValue	materialize() Return a Value containing all the items in the sequence returned by this SequenceIterator.
boolean	moveNext() Move to the next node, without returning it.
Item	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

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)

moveNext

public boolean moveNext()

Move to the next node, without returning it. Returns true if there is a next node, false if the end of the sequence has been reached. After calling this method, the current node may be retrieved using the current() function.

Specified by:

moveNext in interface AxisIterator

next

public Item next()

Get the next item.

Specified by:

next in interface SequenceIterator

Specified by:

next in interface UnfailingIterator

Returns:

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

current

public Item current()

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

Specified by:

current in interface SequenceIterator

Specified by:

current in interface UnfailingIterator

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

Specified by:

position in interface UnfailingIterator

Returns:

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

getLastPosition

public int getLastPosition()

Get the position of the last item in the sequence.

Specified by:

getLastPosition in interface LastPositionFinder

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

iterateAxis

public AxisIterator iterateAxis(byte axis,
                                NodeTest test)

Return an iterator over an axis, starting at the current node.

Specified by:

iterateAxis in interface AxisIterator

Parameters:

axis - the axis to iterate over, using a constant such as Axis.CHILD

test - a predicate to apply to the nodes before returning them.

Throws:

NullPointerException - if there is no current node

atomize

public Value atomize()
              throws XPathException

Return the atomized value of the current node.

Specified by:

atomize in interface AxisIterator

Returns:

the atomized value.

Throws:

NullPointerException - if there is no current node

XPathException

getStringValue

public CharSequence getStringValue()

Return the string value of the current node.

Specified by:

getStringValue in interface AxisIterator

Returns:

the string value, as an instance of CharSequence.

Throws:

NullPointerException - if there is no current node

getAnother

public SequenceIterator getAnother()

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

Specified by:

getAnother in interface SequenceIterator

Specified by:

getAnother in interface UnfailingIterator

Returns:

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

getReverseIterator

public SequenceIterator getReverseIterator()

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

Specified by:

getReverseIterator in interface ReversibleIterator

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

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

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

Returns:

true if there are more nodes