net.sf.saxon.om

Interface SequenceIterator<T extends Item<?>>

All Superinterfaces:

java.lang.AutoCloseable, java.io.Closeable

All Known Subinterfaces:

AtomicIterator, AtomizedValueIterator<T>, AxisIterator, FocusIterator<T>, GroundedIterator<T>, GroupIterator, LookaheadIterator<T>, RegexIterator, ReversibleIterator<T>, UnfailingIterator<T>

All Known Implementing Classes:

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

public interface SequenceIterator<T extends Item<?>>
extends java.io.Closeable

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

Modifier and Type	Method and Description
default void	close() Close the iterator.
default void	forEachOrFail(ItemConsumer<T> consumer) Process all the remaining items delivered by the SequenceIterator using a supplied consumer function.
default int	getProperties() Get properties of this iterator, as a bit-significant integer.
default GroundedValue<T>	materialize() Create a GroundedValue (a sequence materialized in memory) containing all the values delivered by this SequenceIterator.
T	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

T next()
throws XPathException

Get the next item in the sequence. This method changes the state of the iterator.

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

default 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.

For example, the iterator returned by the unparsed-text-lines() function has a close() method that causes the underlying input stream to be closed, whether or not the file has been read to completion.

Closing an iterator is important 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 java.lang.AutoCloseable

Specified by:

close in interface java.io.Closeable

Since:

9.1. Default implementation added in 9.9.

getProperties

default 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. Default implementation added in 9.9.

forEachOrFail

default void forEachOrFail(ItemConsumer<T> consumer)
                    throws XPathException

Process all the remaining items delivered by the SequenceIterator using a supplied consumer function.

Parameters:

consumer - the supplied consumer function

Throws:

XPathException - if either (a) an error occurs obtaining an item from the input sequence, or (b) the consumer throws an exception.

materialize

default GroundedValue<T> materialize()
                              throws XPathException

Create a GroundedValue (a sequence materialized in memory) containing all the values delivered by this SequenceIterator. The method must only be used when the SequenceIterator is positioned at the start. If it is not positioned at the start, then it is implementation-dependant whether the returned sequence contains all the nodes delivered by the SequenceIterator from the beginning, or only those delivered starting at the current position.

It is implementation-dependant whether this method consumes the SequenceIterator. (More specifically, in the current implementation: if the iterator is backed by a GroundedValue, then that value is returned and the iterator is not consumed; otherwise, the iterator is consumed and the method returns the remaining items after the current position only).

Returns:

a sequence containing all the items delivered by this SequenceIterator.

Throws:

XPathException - if reading the SequenceIterator throws an error