net.sf.saxon.om

Interface SequenceIterator

All Known Subinterfaces:

AtomicIterator, AtomizedValueIterator, AxisIterator, FocusIterator, GroundedIterator, GroupIterator, LookaheadIterator, RegexIterator, ReversibleIterator, UnfailingIterator

All Known Implementing Classes:

AdjacentTextNodeMergingIterator, ARegexIterator, ArrayIterator, ATokenIterator, AtomizingIterator, AxiomDocument.FollowingSiblingIterator, AxiomDocument.PrecedingSiblingIterator, AxiomDocumentNodeWrapper.FollowingSiblingIterator, AxiomDocumentNodeWrapper.PrecedingSiblingIterator, AxiomParentNodeWrapper.ChildWrappingIterator, AxiomParentNodeWrapper.DescendantWrappingIterator, AxisAtomizingIterator, AxisIteratorImpl, AxisIteratorOverSequence, BigRangeIterator, BlockIterator, CardinalityCheckingIterator, CompiledBlockIterator, CompiledFilterIterator, ContextMappingIterator, DifferenceEnumeration, DistinctValues.DistinctIterator, DocumentOrderIterator, EmptyIterator, EmptyIterator.OfAtomic, EmptyIterator.OfNodes, ErrorIterator, EveryItemMappingIterator, FilterIterator, FilterIterator.NonNumeric, FocusTrackingIterator, GroupAdjacentIterator, GroupByIterator, GroupByIterator.ManualGroupByIterator, GroupEndingIterator, GroupMatchingIterator, GroupStartingIterator, HomogeneityCheckerIterator, IndexMatcher, InsertBefore.InsertIterator, IntersectionEnumeration, ItemMappingIterator, IteratorIterator, JRegexIterator, JTokenIterator, ListIterator, ListIterator.Atomic, LookaheadIteratorImpl, ManualGroupIterator, ManualIterator, MappingIterator, MemoClosure.ProgressiveIterator, MemoSequence.ProgressiveIterator, MergeGroupingIterator, MergeGroupingIterator.ManualMergeGroupingIterator, MergeIterator, MultithreadedContextMappingIterator, MultithreadedItemMappingIterator, Navigator.AncestorEnumeration, Navigator.AxisFilter, Navigator.DescendantEnumeration, Navigator.EmptyTextFilter, Navigator.FollowingEnumeration, Navigator.PrecedingEnumeration, NodeWrappingAxisIterator, OneToOneMappingIterator, PrependIterator, RangeIterator, Remove.RemoveIterator, ReturnClauseIterator, ReverseListIterator, ReverseRangeIterator, SequenceComposer, SingleAtomicIterator, SingleNodeIterator, SingletonIterator, SortedGroupIterator, SortedIterator, SteppingNavigator.DescendantAxisIterator, StringTokenIterator, StringValue.CharacterIterator, StringValue.UnicodeCharacterIterator, SubsequenceIterator, TailIterator, TextLinesIterator, UnionEnumeration, UnparsedTextIterator, UntypedAtomizingIterator, ValueTailIterator, VirtualCopy.VirtualCopier, WrappingIterator

public interface SequenceIterator

A SequenceIterator is used to iterate over any XPath 2 sequence (of values or nodes). To get the next item in a sequence, call next(); if this returns null, you've reached the end of the sequence.

The objects returned by the SequenceIterator will generally be either nodes (class NodeInfo), singleton values (class AtomicValue), or function items: these are represented collectively by the interface Item.

The interface to SequenceIterator is changed in Saxon 9.6 to drop support for the current() and position() methods. Internal iterators no longer need to maintain the values of the current item or the current position. This information is needed (in general) only for an iterator that acts as the current focus; that is, an iterator stored as the current iterator in an XPathContext. SequenceIterators than maintain the value of position() and last() are represented by the interface FocusIterator.

Since:

8.4; significant changes in 9.6.

Author:

Michael H. Kay

Field Summary

Fields

Modifier and Type	Field and Description
static int	ATOMIZING Property value: the iterator can deliver an atomized result.
static int	GROUNDED Property value: the iterator is "grounded".
static int	LAST_POSITION_FINDER Property value: the iterator knows the number of items that it will deliver.
static int	LOOKAHEAD Property value: the iterator knows whether there are more items still to come.

Method Summary

Methods

Modifier and Type	Method and Description
void	close() Close the iterator.
SequenceIterator	getAnother() Get another SequenceIterator that iterates over the same items as the original, but which is repositioned at the start of the sequence.
int	getProperties() Get properties of this iterator, as a bit-significant integer.
Item	next() Get the next item in the sequence.

Field Detail

GROUNDED

static final int GROUNDED

Property value: the iterator is "grounded". This means that (a) the iterator must be an instance of GroundedIterator, and (b) the implementation of the materialize() method must be efficient (in particular, it should not involve the creation of new objects)

See Also:

Constant Field Values

LAST_POSITION_FINDER

static final int LAST_POSITION_FINDER

Property value: the iterator knows the number of items that it will deliver. This means that (a) the iterator must be an instance of LastPositionFinder, and (b) the implementation of the getLastPosition() method must be efficient (in particular, it should take constant time, rather than time proportional to the length of the sequence)

See Also:

Constant Field Values

LOOKAHEAD

static final int LOOKAHEAD

Property value: the iterator knows whether there are more items still to come. This means that (a) the iterator must be an instance of LookaheadIterator, and (b) the implementation of the hasNext() method must be efficient (more efficient than the client doing it)

See Also:

Constant Field Values

ATOMIZING

static final int ATOMIZING

Property value: the iterator can deliver an atomized result. This means that the iterator must be an instance of AtomizingIterator.

See Also:

Constant Field Values

Method Detail

next

Item next()
          throws XPathException

Get the next item in the sequence. This method changes the state of the iterator, in particular it affects the result of subsequent calls of position() and current().

Returns:

the next item, or null if there are no more items. Once a call on next() has returned null, no further calls should be made. The preferred action for an iterator if subsequent calls on next() are made is to return null again, and all implementations within Saxon follow this rule.

Throws:

XPathException - if an error occurs retrieving the next item

Since:

8.4

close

void close()

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.)

Since:

9.1

getAnother

SequenceIterator getAnother()
                            throws XPathException

Get another SequenceIterator that iterates over the same items as the original, but which is repositioned at the start of the sequence.

This method allows access to all the items in the sequence without disturbing the current position of the iterator. Internally, its main use is in evaluating the last() function.

This method does not change the state of the iterator.

Some implementations of this method may regenerate the input sequence, creating new nodes with different identity from the original. This is not recommended, but is hard to prevent. This causes no problem for the primary usage of this method to support the last() function, but it has been known to cause trouble in other situations.

Returns:

a SequenceIterator that iterates over the same items, positioned before the first item

Throws:

XPathException - if any error occurs

Since:

8.4

getProperties

int getProperties()

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

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.

Since:

8.6