net.sf.saxon.expr
Class CardinalityCheckingIterator

java.lang.Object
  net.sf.saxon.expr.CardinalityCheckingIterator

All Implemented Interfaces:

SequenceIterator

public final class CardinalityCheckingIterator
extends Object
implements SequenceIterator

CardinalityCheckingIterator returns the items in an underlying sequence unchanged, but checks that the number of items conforms to the required cardinality. Because cardinality checks are required to take place even if the consumer of the sequence does not require all the items, we read the first two items at initialization time. This is sufficient to perform the checks; after that we can simply return the items from the base sequence.

Field Summary

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

GROUNDED, LAST_POSITION_FINDER, LOOKAHEAD

Constructor Summary

CardinalityCheckingIterator(SequenceIterator base, int requiredCardinality, RoleLocator role, SourceLocator locator)
Construct an CardinalityCheckingIterator that will return the same items as the base sequence, checking how many there are

Method Summary

void	close() Close the iterator.
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	getProperties() Get properties of this iterator, as a bit-significant integer.
Item	next() Get the next item in the sequence.
int	position() Get the current position.

Methods inherited from class java.lang.Object

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

Constructor Detail

CardinalityCheckingIterator

public CardinalityCheckingIterator(SequenceIterator base,
                                   int requiredCardinality,
                                   RoleLocator role,
                                   SourceLocator locator)
                            throws XPathException

Construct an CardinalityCheckingIterator that will return the same items as the base sequence, checking how many there are

Parameters:

base - the base iterator

requiredCardinality - the required Cardinality

Throws:

XPathException

Method Detail

next

public Item 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

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.

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.