- All Implemented Interfaces:
public class SubsequenceIterator extends java.lang.Object implements SequenceIterator, LastPositionFinder, LookaheadIteratorA SubsequenceIterator selects a subsequence of a sequence
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description
close()Close the iterator.
getLength()Get the last position (that is, the number of items in the sequence).
hasNext()Test whether there are any more items available in the sequence
make(SequenceIterator base, int min, int max)Static factory method.
next()Get the next item if there is one
supportsGetLength()Ask whether this iterator supports use of the
supportsHasNext()Ask whether the hasNext() method can be called.
public static SequenceIterator make(SequenceIterator base, int min, int max) throws XPathExceptionStatic factory method. Creates a SubsequenceIterator, unless for example the base Iterator is an ArrayIterator, in which case it optimizes by creating a new ArrayIterator directly over the underlying array. This optimization is important when doing recursion over a node-set using repeated calls of
base- An iteration of the items to be filtered
min- The position of the first item to be included (base 1)
max- The position of the last item to be included (base 1)
- an iterator over the requested subsequence
XPathException- if a dynamic error occurs
public boolean supportsHasNext()Description copied from interface:
LookaheadIteratorAsk whether the hasNext() method can be called. This method must be called before calling hasNext(), because some iterators implement this interface, but only support look-ahead under particular circumstances (this is usually because they delegate to another iterator)
public boolean hasNext()Test whether there are any more items available in the sequence
public Item next()Get the next item if there is one
- Specified by:
- 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.
public void close()Description copied from interface:
SequenceIteratorClose 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
SequenceIterator.next()returns null, the iterator will be closed automatically. An explicit call on
SequenceIterator.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
public boolean supportsGetLength()Ask whether this iterator supports use of the
getLength()method. This method should always be called before calling
getLength(), because an iterator that implements this interface may support use of
getLength()in some situations and not in others