net.sf.saxon.expr.sort
Class SortedIterator

java.lang.Object
  net.sf.saxon.expr.sort.SortedIterator

All Implemented Interfaces:

LastPositionFinder, Sortable, SequenceIterator, LookaheadIterator

Direct Known Subclasses:

SortedGroupIterator, SortedTupleIterator

public class SortedIterator
extends Object
implements SequenceIterator, LastPositionFinder, LookaheadIterator, Sortable

Class to do a sorted iteration

Field Summary

protected SequenceIterator	base
protected AtomicComparer[]	comparators
protected XPathContext	context
protected int	count
protected Object[]	nodeKeys
protected int	position
protected int	recordSize
protected SortKeyEvaluator	sortKeyEvaluator

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

GROUNDED, LAST_POSITION_FINDER, LOOKAHEAD

Constructor Summary

SortedIterator(XPathContext context, SequenceIterator base, SortKeyEvaluator sortKeyEvaluator, AtomicComparer[] comparators)
Create a sorted iterator

Method Summary

protected void	buildArray() Create an array holding the items to be sorted and the values of their sort keys
void	close() Close the iterator.
int	compare(int a, int b) Compare two items in sorted sequence (needed to implement the Sortable interface)
Item	current() Get the current value in the sequence (the one returned by the most recent call on next()).
SequenceIterator	getAnother() Get another SequenceIterator that iterates over the same items as the original, but which is repositioned at the start of the sequence.
int	getLastPosition() 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.
boolean	hasNext() Determine whether there are more items to come.
Item	next() Get the next item, in sorted order
int	position() Get the current position.
void	setHostLanguage(int language) Set the host language
void	swap(int a, int b) Swap two items (needed to implement the Sortable interface)

Methods inherited from class java.lang.Object

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

Field Detail

base

protected SequenceIterator base

sortKeyEvaluator

protected SortKeyEvaluator sortKeyEvaluator

comparators

protected AtomicComparer[] comparators

recordSize

protected int recordSize

nodeKeys

protected Object[] nodeKeys

count

protected int count

position

protected int position

context

protected XPathContext context

Constructor Detail

SortedIterator

public SortedIterator(XPathContext context,
                      SequenceIterator base,
                      SortKeyEvaluator sortKeyEvaluator,
                      AtomicComparer[] comparators)

Create a sorted iterator

Parameters:

context - the dynamic XPath evaluation context

base - an iterator over the sequence to be sorted

sortKeyEvaluator - an object that allows the n'th sort key for a given item to be evaluated

comparators - an array of AtomicComparers, one for each sort key, for comparing sort key values

Method Detail

setHostLanguage

public void setHostLanguage(int language)

Set the host language

Parameters:

language - the host language (for example Configuration.XQUERY)

hasNext

public boolean hasNext()

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 Item next()
          throws XPathException

Get the next item, in sorted order

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.

getLastPosition

public int getLastPosition()
                    throws XPathException

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 result of getProperties() on the iterator includes the bit setting SequenceIterator.LAST_POSITION_FINDER

Specified by:

getLastPosition in interface LastPositionFinder

Throws:

XPathException

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 SequenceIterator 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.

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

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.

buildArray

protected void buildArray()
                   throws XPathException

Create an array holding the items to be sorted and the values of their sort keys

Throws:

XPathException

compare

public int compare(int a,
                   int b)

Compare two items in sorted 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 items (needed to implement the Sortable interface)

Specified by:

swap in interface Sortable