net.sf.saxon.om
Class EmptyIterator

java.lang.Object
  net.sf.saxon.om.EmptyIterator

All Implemented Interfaces:

AxisIterator, GroundedIterator, LastPositionFinder, LookaheadIterator, ReversibleIterator, SequenceIterator

public class EmptyIterator

extends java.lang.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

ATOMIZABLE, GROUNDED, LAST_POSITION_FINDER, LOOKAHEAD

Constructor Summary

EmptyIterator()

Method Summary

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.
boolean	hasNext() Determine whether there are more items to come.
Value	materialize() Return a Value containing all the items in the sequence returned by this SequenceIterator.
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

Constructor Detail

EmptyIterator

public EmptyIterator()

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)

next

public Item next()

Get the next item. This method should not be called unless hasNext() returns true.

Specified by:

next in interface AxisIterator

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 AxisIterator

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 AxisIterator

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

getAnother

public SequenceIterator getAnother()

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

Specified by:

getAnother in interface AxisIterator

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 GROUNDED, LAST_POSITION_FINDER, and 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 Value 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