- All Implemented Interfaces:
public class SingletonIterator extends java.lang.Object implements SequenceIterator, FocusIterator, ReversibleIterator, LastPositionFinder, GroundedIterator, LookaheadIteratorSingletonIterator: an iterator over a sequence exactly one value
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description
close()Close the iterator.
current()Get the current value in the sequence (the one returned by the most recent call on next()).
getLength()Get the position of the last item in the sequence
getResidue()Return a GroundedValue containing all the remaining items in the sequence returned by this SequenceIterator, starting at the current position.
getReverseIterator()Get a new SequenceIterator that returns the same items in reverse order.
hasNext()Determine whether there are more items to come.
isActuallyGrounded()Ask if the iterator is actually grounded.
makeIterator(Item item)Factory method.
materialize()Return a Value containing all the items in the sequence returned by this SequenceIterator
next()Get the next item in the sequence.
position()Get the current position.
supportsGetLength()Ask whether this iterator supports use of the
supportsHasNext()Ask whether the hasNext() method can be called.
public SingletonIterator(Item value)Constructor
value- the item to iterate over. Must not be null.
public static SequenceIterator makeIterator(Item item)Factory method.
item- the item to iterate over
- a SingletonIterator over the supplied item, or an EmptyIterator if the supplied item is null.
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()Determine 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.
public Item next()Description copied from interface:
SequenceIteratorGet 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 Item current()Get the current value in the sequence (the one returned by the most recent call on next()). This will be null before the first call of next(). This method does not change the state of the iterator.
public int position()Get the current position. This will usually be zero before the first call on next(), otherwise it will be the number of times that next() has been called. Once next() has returned null, the preferred action is for subsequent calls on position() to return -1, but not all existing implementations follow this practice. (In particular, the EmptyIterator is stateless, and always returns 0 as the value of position(), whether or not next() has been called.)
This method does not change the state of the iterator.
- Specified by:
- the current position, the position of the item returned by the most recent call of next(). This is 1 after next() has been successfully called once, 2 after it has been called twice, and so on. If next() has never been called, the method returns zero. If the end of the sequence has been reached, the value returned will always be <= 0; the preferred value is -1.
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()Description copied from interface:
LastPositionFinderAsk whether this iterator supports use of the
LastPositionFinder.getLength()method. This method should always be called before calling
LastPositionFinder.getLength(), because an iterator that implements this interface may support use of
LastPositionFinder.getLength()in some situations and not in others
public int getLength()Get the position of the last item in the sequence
public boolean isActuallyGrounded()Description copied from interface:
GroundedIteratorAsk if the iterator is actually grounded. This method must be called before calling
GroundedIterator.getResidue(), because the iterator might be grounded under some conditions and not others (usually when it delegates to another iterator)
public SingletonIterator getReverseIterator()Description copied from interface:
ReversibleIteratorGet a new SequenceIterator that returns the same items in reverse order. If this SequenceIterator is an AxisIterator, then the returned SequenceIterator must also be an AxisIterator.
public Item getValue()
public GroundedValue materialize()Return a Value containing all the items in the sequence returned by this SequenceIterator
public GroundedValue getResidue()Description copied from interface:
GroundedIteratorReturn a GroundedValue containing all the remaining items in the sequence returned by this SequenceIterator, starting at the current position. This should be an "in-memory" value, not a Closure. This method does not change the state of the iterator (in particular, it does not consume the iterator).