net.sf.saxon.om

Class MemoSequence.ProgressiveIterator

java.lang.Object

net.sf.saxon.om.MemoSequence.ProgressiveIterator

All Implemented Interfaces:

LastPositionFinder, SequenceIterator, GroundedIterator

Enclosing class:

MemoSequence

public final class MemoSequence.ProgressiveIterator
extends Object
implements SequenceIterator, LastPositionFinder, GroundedIterator

A ProgressiveIterator starts by reading any items already held in the reservoir; when the reservoir is exhausted, it reads further items from the inputIterator, copying them into the reservoir as they are read.

Field Summary

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

GROUNDED, LAST_POSITION_FINDER, LOOKAHEAD

Constructor Summary

Constructors

Constructor and Description
MemoSequence.ProgressiveIterator() Create a ProgressiveIterator

Method Summary

Methods

Modifier and Type	Method and Description
void	close() Close the iterator.
Item	current() Get the current value in the sequence (the one returned by the most recent call on next()).
MemoSequence.ProgressiveIterator	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.
GroundedValue	materialize() Return a value containing all the items in the sequence returned by this SequenceIterator
Item	next() Get the next item in the sequence.
int	position() Get the current position.

Methods inherited from class java.lang.Object

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

Constructor Detail

MemoSequence.ProgressiveIterator

public MemoSequence.ProgressiveIterator()

Create a ProgressiveIterator

Method Detail

next

public Item next()
          throws XPathException

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

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.

Throws:

XPathException - if an error occurs retrieving the next item

current

public Item 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

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()

Description copied from interface: SequenceIterator

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:

position in interface SequenceIterator

Returns:

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.

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

getAnother

public MemoSequence.ProgressiveIterator 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.

Some implementations of this method may regenerate the input sequence, creating new nodes with different identity from the original. This is not recommended, but is hard to prevent. This causes no problem for the primary usage of this method to support the last() function, but it has been known to cause trouble in other situations.

Specified by:

getAnother in interface SequenceIterator

Returns:

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

getLength

public int getLength()
              throws XPathException

Get the last position (that is, the number of items in the sequence)

Specified by:

getLength in interface LastPositionFinder

Returns:

the number of items in the sequence

Throws:

XPathException - if an error occurs evaluating the sequence in order to determine the number of items

materialize

public GroundedValue materialize()

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

Specified by:

materialize in interface GroundedIterator

Returns:

the corresponding value

getProperties

public int getProperties()

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

Specified by:

getProperties in interface SequenceIterator

Returns:

the properties of this iterator. This will be some combination of properties such as SequenceIterator.GROUNDED and SequenceIterator.LAST_POSITION_FINDER. It is always acceptable to return the value zero, indicating that there are no known special properties.