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public interface SequenceIterator extends java.io.CloseableA 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
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
- 8.4. Significant changes in 9.6. Generics added in 9.9, removed again in 10.0.
getProperties() method dropped in 11 (instead, callers should check whether the
iterator implements a more specific interface such as
Item next()Get the next item in the sequence. This method changes the state of the iterator.
- 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.
UncheckedXPathException- if an error occurs retrieving the next item
- 8.4. Changed in 11 so it no longer throws a checked exception; instead, any error that occurs is thrown as an unchecked exception.
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.
Closing an iterator is not necessary if the iterator is read to completion: if a call on
next()returns null, the iterator will be closed automatically. An explicit call on
close()is needed only when iteration is abandoned prematurely.
It is not possible to guarantee that an iterator that is not read to completion or will be closed. For example, if a lazy-evaluated variable
$varis passed to a user-written function, the function may access
$varonly; we have no way of knowing whether further items will be read. For this reason, any
SequenceIteratorthat holds resources which need to be closed should use the
Cleaner, and resources held by a
SequenceIteratorshould be registered with the
Cleaner; if the
SequenceIteratoris then garbage-collected without being closed, the
Cleanerwill ensure that the underlying resources are closed. (An example of a
SequenceIteratorthat uses this mechanism is the
- Specified by:
- Specified by:
- 9.1. Default implementation added in 9.9.