net.sf.saxon.tree.iter
Class SingletonIterator<T extends Item>

java.lang.Object
  net.sf.saxon.tree.iter.SingletonIterator<T>

All Implemented Interfaces:

LastPositionFinder<T>, SequenceIterator<T>, GroundedIterator<T>, LookaheadIterator<T>, ReversibleIterator<T>, UnfailingIterator<T>

public class SingletonIterator<T extends Item>
extends Object
implements SequenceIterator<T>, UnfailingIterator<T>, ReversibleIterator<T>, LastPositionFinder<T>, GroundedIterator<T>, LookaheadIterator<T>

SingletonIterator: an iterator over a sequence of zero or one values

Field Summary

Fields inherited from interface net.sf.saxon.om.SequenceIterator

GROUNDED, LAST_POSITION_FINDER, LOOKAHEAD

Method Summary

void	close() Close the iterator.
T	current() Get the current value in the sequence (the one returned by the most recent call on next()).
SingletonIterator<T>	getAnother() Get another SequenceIterator that iterates over the same items as the original, but which is repositioned at the start of the sequence.
int	getLength() Get the last position (that is, the number of items in the sequence).
int	getProperties() Get properties of this iterator, as a bit-significant integer.
SingletonIterator<T>	getReverseIterator() Get a new SequenceIterator that returns the same items in reverse order.
T	getValue()
boolean	hasNext() Determine whether there are more items to come.
static <T extends Item> UnfailingIterator<T>	makeIterator(T item) Factory method.
GroundedValue	materialize() Return a Value containing all the items in the sequence returned by this SequenceIterator
T	next() Get the next item in the sequence.
int	position() Return the current position in the sequence.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

makeIterator

public static <T extends Item> UnfailingIterator<T> makeIterator(T item)

Factory method.

Parameters:

item - the item to iterate over

Returns:

a SingletonIterator over the supplied item, or an EmptyIterator if the supplied item is null.

hasNext

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.

Specified by:

hasNext in interface LookaheadIterator<T extends Item>

Returns:

true if there are more items

next

public T next()

Description copied from interface: SequenceIterator

Get the next item in the sequence. This method changes the state of the iterator, in particular it affects the result of subsequent calls of position() and current().

Specified by:

next in interface SequenceIterator<T extends Item>

Specified by:

next in interface UnfailingIterator<T extends Item>

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.

current

public T current()

Description copied from interface: SequenceIterator

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.

Specified by:

current in interface SequenceIterator<T extends Item>

Specified by:

current in interface UnfailingIterator<T extends Item>

Returns:

the current item, the one most recently returned by a call on next(). Returns null if next() has not been called, or if the end of the sequence has been reached.

position

public int position()

Return the current position in the sequence.

Specified by:

position in interface SequenceIterator<T extends Item>

Specified by:

position in interface UnfailingIterator<T extends Item>

Returns:

0 before the first call on next(); 1 before the second call on next(); -1 after the second call on next().

getLength

public int getLength()

Description copied from interface: LastPositionFinder

Get the last position (that is, the number of items in the sequence). This method is non-destructive: it does not change the state of the iterator. The result is undefined if the next() method of the iterator has already returned null. This method must not be called unless the result of getProperties() on the iterator includes the bit setting SequenceIterator.LAST_POSITION_FINDER

Specified by:

getLength in interface LastPositionFinder<T extends Item>

Returns:

the number of items in the sequence

close

public void close()

Description copied from interface: SequenceIterator

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.

(Currently, closing an iterator is important only 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 SequenceIterator<T extends Item>

getAnother

public SingletonIterator<T> getAnother()

Description copied from interface: SequenceIterator

Get another SequenceIterator that iterates over the same items as the original, but which is repositioned at the start of the sequence.

This method allows access to all the items in the sequence without disturbing the current position of the iterator. Internally, its main use is in evaluating the last() function.

This method does not change the state of the iterator.

Specified by:

getAnother in interface SequenceIterator<T extends Item>

Specified by:

getAnother in interface UnfailingIterator<T extends Item>

Returns:

a SequenceIterator that iterates over the same items, positioned before the first item

getReverseIterator

public SingletonIterator<T> getReverseIterator()

Description copied from interface: ReversibleIterator

Get 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.

Specified by:

getReverseIterator in interface ReversibleIterator<T extends Item>

Returns:

an iterator over the items in reverse order

getValue

public T getValue()

materialize

public GroundedValue materialize()

Return a Value containing all the items in the sequence returned by this SequenceIterator

Specified by:

materialize in interface GroundedIterator<T extends Item>

Returns:

the corresponding Value. If the value is a closure or a function call package, it will be evaluated and expanded.

getProperties

public int getProperties()

Get properties of this iterator, as a bit-significant integer.

Specified by:

getProperties in interface SequenceIterator<T extends Item>

Returns:

the properties of this iterator. This will be some combination of properties such as SequenceIterator.GROUNDED, SequenceIterator.LAST_POSITION_FINDER, and SequenceIterator.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.