net.sf.saxon.expr.sort

Class DocumentOrderIterator

java.lang.Object

net.sf.saxon.expr.sort.DocumentOrderIterator

All Implemented Interfaces:

Sortable, SequenceIterator

public final class DocumentOrderIterator
extends Object
implements SequenceIterator, Sortable

DocumentOrderIterator takes as input an iteration of nodes in any order, and returns as output an iteration of the same nodes in document order, eliminating any duplicates.

Field Summary

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

ATOMIZING, GROUNDED, LAST_POSITION_FINDER, LOOKAHEAD

Constructor Summary

Constructors

Constructor and Description
DocumentOrderIterator(SequenceIterator base, ItemOrderComparer comparer) Iterate over a sequence in document order.

Method Summary

Methods

Modifier and Type	Method and Description
void	close() Close the iterator.
int	compare(int a, int b) Compare two nodes in document sequence (needed to implement the Sortable interface)
DocumentOrderIterator	getAnother() Get another SequenceIterator that iterates over the same items as the original, but which is repositioned at the start of the sequence.
int	getProperties() Get properties of this iterator, as a bit-significant integer.
NodeInfo	next() Get the next item in the sequence.
void	swap(int a, int b) Swap two nodes (needed to implement the Sortable interface)

Methods inherited from class java.lang.Object

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

Constructor Detail

DocumentOrderIterator

public DocumentOrderIterator(SequenceIterator base,
                     ItemOrderComparer comparer)
                      throws XPathException

Iterate over a sequence in document order.

Parameters:

base - the input sequence to be sorted

comparer - the comparer used for comparing node positions

Throws:

XPathException - if the input sequence cannot be evaluated

Method Detail

compare

public int compare(int a,
          int b)

Compare two nodes in document sequence (needed to implement the Sortable interface)

Specified by:

compare in interface Sortable

Returns:

<0 if obj[a]0 if obj[a]>obj[b]

swap

public void swap(int a,
        int b)

Swap two nodes (needed to implement the Sortable interface)

Specified by:

swap in interface Sortable

next

public NodeInfo 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

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, 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.

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 DocumentOrderIterator getAnother()
                                 throws XPathException

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

Throws:

XPathException - if any error occurs