net.sf.saxon.expr.sort

Class MergeIterator

java.lang.Object

net.sf.saxon.expr.sort.MergeIterator

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable, 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.

Constructor Summary

Constructors

Constructor and Description
MergeIterator(SequenceIterator p1, SequenceIterator p2, java.util.Comparator<ObjectValue<ItemWithMergeKeys>> comparer) Create the iterator.

Method Summary

Modifier and Type	Method and Description
void	close() Close the iterator.
void	discharge() Calling this method instructs the iterator to release any resources it holds, while still remaining able to deliver the remaining items in the sequence.
boolean	hasNext() Determine whether there are more items to come.
ObjectValue<ItemWithMergeKeys>	next() Get the next item in the sequence.
boolean	supportsHasNext() Ask whether the hasNext() method can be called.

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,
                     java.util.Comparator<ObjectValue<ItemWithMergeKeys>> 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

supportsHasNext

public boolean supportsHasNext()

Description copied from interface: LookaheadIterator

Ask 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)

Specified by:

supportsHasNext in interface LookaheadIterator

Returns:

true if the LookaheadIterator.hasNext() method is available

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 LookaheadIterator.supportsHasNext() is true.

Specified by:

hasNext in interface LookaheadIterator

Returns:

true if there are more items in the sequence

next

public ObjectValue<ItemWithMergeKeys> next()

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.

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.

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.

Specified by:

close in interface java.io.Closeable

Specified by:

close in interface java.lang.AutoCloseable

Specified by:

close in interface SequenceIterator

discharge

public void discharge()

Description copied from interface: SequenceIterator

Calling this method instructs the iterator to release any resources it holds, while still remaining able to deliver the remaining items in the sequence. This may require the iterator to calculate the rest of the sequence eagerly. The method is called by a client if it anticipates that it might not read the iterator to completion, but it cannot guarantee that SequenceIterator.close() will be called when no more items are needed.

Specified by:

discharge in interface SequenceIterator