- All Implemented Interfaces:
public class LookaheadIteratorImpl extends java.lang.Object implements LookaheadIteratorThis class wraps any sequence iterator, turning it into a lookahead iterator, by looking ahead one item
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description
close()Close the iterator.
discharge()Calling this method instructs the iterator to release any resources it holds, while still remaining able to deliver the remaining items in the sequence.
hasNext()Determine whether there are more items to come.
next()Get the next item in the sequence.
supportsHasNext()Ask whether the hasNext() method can be called.
public static LookaheadIterator makeLookaheadIterator(SequenceIterator base) throws XPathException
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()Description copied from interface:
LookaheadIteratorDetermine 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.
This method must not be called unless the result of
public Item next()Get the next item in the sequence. This method changes the state of the iterator.
- 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()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
SequenceIterator.next()returns null, the iterator will be closed automatically. An explicit call on
SequenceIterator.close()is needed only when iteration is abandoned prematurely.
public void discharge()Calling this method instructs the iterator to release any resources it holds, while still remaining able to deliver the remaining items in the sequence. This may require the iterator to calculate the rest of the sequence eagerly. The method is called by a client if it anticipates that it might not read the iterator to completion, but it cannot guarantee that
SequenceIterator.close()will be called when no more items are needed.