net.sf.saxon.tree.iter

Class EmptyIterator

java.lang.Object

net.sf.saxon.tree.iter.EmptyIterator

All Implemented Interfaces:

LastPositionFinder, AtomizedValueIterator, SequenceIterator, GroundedIterator, LookaheadIterator, ReversibleIterator, UnfailingIterator

Direct Known Subclasses:

EmptyIterator.OfAtomic, EmptyIterator.OfNodes

public class EmptyIterator
extends java.lang.Object
implements SequenceIterator, ReversibleIterator, LastPositionFinder, GroundedIterator, LookaheadIterator, UnfailingIterator, AtomizedValueIterator

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.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	EmptyIterator.OfAtomic An empty iterator for use where a sequence of atomic values is required
static class	EmptyIterator.OfNodes An empty iterator for use where a sequence of nodes is required

Field Summary

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

ATOMIZING, GROUNDED, LAST_POSITION_FINDER, LOOKAHEAD

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	EmptyIterator() Protected constructor

Method Summary

Modifier and Type	Method and Description
void	close() Close the iterator.
static EmptyIterator	emptyIterator()
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.
GroundedValue	getResidue() Return a GroundedValue containing all the remaining items in the sequence returned by this SequenceIterator, starting at the current position.
EmptyIterator	getReverseIterator() Get another iterator over the same items, in reverse order.
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.
Item	next() Get the next item.
AtomicSequence	nextAtomizedValue() Deliver the atomic value that is next in the atomized result

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 EmptyIterator emptyIterator()

nextAtomizedValue

public AtomicSequence nextAtomizedValue()
                                 throws XPathException

Deliver the atomic value that is next in the atomized result

Specified by:

nextAtomizedValue in interface AtomizedValueIterator

Returns:

the next atomic value

Throws:

XPathException - if a failure occurs reading or atomizing the next value

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.

getLength

public int getLength()

Get the position of the last item in the sequence.

Specified by:

getLength 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

getReverseIterator

public EmptyIterator 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

getResidue

public GroundedValue getResidue()
                         throws XPathException

Description copied from interface: GroundedIterator

Return a GroundedValue containing all the remaining items in the sequence returned by this SequenceIterator, starting at the current position. This should be an "in-memory" value, not a Closure.

Specified by:

getResidue in interface GroundedIterator

Returns:

the corresponding Value

Throws:

XPathException - in the cases of subclasses (such as the iterator over a MemoClosure) which cause evaluation of expressions while materializing the 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