net.sf.saxon.expr.sort

Class MergeIterator

java.lang.Object

net.sf.saxon.expr.sort.MergeIterator

All Implemented Interfaces:

SequenceIterator, LookaheadIterator

public class MergeIterator
extends java.lang.Object
implements SequenceIterator, LookaheadIterator

An iterator representing the sorted merge of two merge inputs, retaining all duplicates. This iterator simply returns the items from all the inputs merged into a single sequence; it does not do any grouping of adjacent items that share the same merge key.

Field Summary

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

ATOMIZING, GROUNDED, LAST_POSITION_FINDER, LOOKAHEAD

Constructor Summary

Constructors

Constructor and Description
MergeIterator(SequenceIterator p1, SequenceIterator p2, ItemOrderComparer comparer) Create the iterator.

Method Summary

Modifier and Type	Method and Description
void	close() Close the iterator.
int	getProperties() Get properties of this iterator, as a bit-significant integer.
boolean	hasNext() Determine whether there are more items to come.
ObjectValue<ItemWithMergeKeys>	next() Get the next item in the sequence.

Methods inherited from class java.lang.Object

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

Constructor Detail

MergeIterator

public MergeIterator(SequenceIterator p1,
                     SequenceIterator p2,
                     ItemOrderComparer comparer)
              throws XPathException

Create the iterator. The two input iterators must return nodes in merge key order for this to work.

Parameters:

p1 - iterator over the first operand sequence (in document order)

p2 - iterator over the second operand sequence

comparer - used to test whether nodes are in document order. Different versions are used for intra-document and cross-document operations

Throws:

XPathException - if an error occurs reading from either input iterator

Method Detail

hasNext

public boolean hasNext()

Description copied from interface: LookaheadIterator

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.

This method must not be called unless the result of getProperties() on the iterator includes the bit setting SequenceIterator.LOOKAHEAD

Specified by:

hasNext in interface LookaheadIterator

Returns:

true if there are more items in the sequence

next

public ObjectValue<ItemWithMergeKeys> next()
                                    throws XPathException

Description copied from interface: SequenceIterator

Get the next item in the sequence. This method changes the state of the iterator.

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

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

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.