Package net.sf.saxon.expr.sort

Class GroupAdjacentIterator

java.lang.Object

net.sf.saxon.expr.sort.GroupAdjacentIterator

All Implemented Interfaces:

Closeable, AutoCloseable, LastPositionFinder, GroupIterator, SequenceIterator, LookaheadIterator

public class GroupAdjacentIterator
extends Object
implements GroupIterator, LastPositionFinder, LookaheadIterator

A GroupAdjacentIterator iterates over a sequence of groups defined by xsl:for-each-group group-adjacent="x". The groups are returned in order of first appearance.

Each step of this iterator advances to the first item of the next group, leaving the members of that group in a saved list.

Constructor Summary

Constructors

Constructor	Description
GroupAdjacentIterator(PullEvaluator select, Expression keyExpression, XPathContext baseContext, StringCollator collator, boolean composite)

Method Summary

Modifier and Type	Method	Description
void	close()	Close the iterator.
GroundedValue	currentGroup()	Get a sequence containing the members of the current group, in population order.
AtomicSequence	getCurrentGroupingKey()	Get the grouping key of the current group
int	getLength()	Get the last position (that is, the number of items in the sequence).
ManualGroupIterator	getSnapShot(XPathContext context)	Get a pseudo-iterator which represents a snapshot of this sequence at the current position
boolean	hasNext()	Determine whether there are more items to come.
Item	next()	Get the next item in the sequence.
boolean	supportsGetLength()	Ask whether this iterator supports use of the LastPositionFinder.getLength() method.
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 Details

GroupAdjacentIterator

public GroupAdjacentIterator(PullEvaluator select,
 Expression keyExpression,
 XPathContext baseContext,
 StringCollator collator,
 boolean composite)
                      throws XPathException

Throws:

XPathException

Method Details

supportsGetLength

public boolean supportsGetLength()

Description copied from interface: LastPositionFinder

Ask whether this iterator supports use of the LastPositionFinder.getLength() method. This method should always be called before calling LastPositionFinder.getLength(), because an iterator that implements this interface may support use of LastPositionFinder.getLength() in some situations and not in others

Specified by:

supportsGetLength in interface LastPositionFinder

Returns:

true if the LastPositionFinder.getLength() method can be called to determine the length of the underlying sequence.

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 LastPositionFinder.supportsGetLength() has been called and has returned true.

Specified by:

getLength in interface LastPositionFinder

Returns:

the number of items in the sequence

getCurrentGroupingKey

public AtomicSequence getCurrentGroupingKey()

Description copied from interface: GroupIterator

Get the grouping key of the current group

Specified by:

getCurrentGroupingKey in interface GroupIterator

Returns:

the current grouping key in the case of group-by or group-adjacent, or null in the case of group-starting-with and group-ending-with

currentGroup

public GroundedValue currentGroup()
                           throws XPathException

Description copied from interface: GroupIterator

Get a sequence containing the members of the current group, in population order. This may be a MemoSequence rather than a grounded value

Specified by:

currentGroup in interface GroupIterator

Returns:

a sequence containing all the members of the current group, in population order.

Throws:

XPathException - if a dynamic error occurs

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 Item 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.

It is not possible to guarantee that an iterator that is not read to completion or will be closed. For example, if a lazy-evaluated variable $var is passed to a user-written function, the function may access $var[1] only; we have no way of knowing whether further items will be read. For this reason, any SequenceIterator that holds resources which need to be closed should use the Cleaner mechanism. The Configuration holds a Cleaner, and resources held by a SequenceIterator should be registered with the Cleaner; if the SequenceIterator is then garbage-collected without being closed, the Cleaner will ensure that the underlying resources are closed. (An example of a SequenceIterator that uses this mechanism is the UnparsedTextIterator).

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Specified by:

close in interface SequenceIterator

getSnapShot

public ManualGroupIterator getSnapShot(XPathContext context)

Description copied from interface: GroupIterator

Get a pseudo-iterator which represents a snapshot of this sequence at the current position

Specified by:

getSnapShot in interface GroupIterator

Parameters:

context - the XPath context

Returns:

the snapshot sequence