net.sf.saxon.expr
Class FilterIterator

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

All Implemented Interfaces:

SequenceIterator

Direct Known Subclasses:

FilterIterator.NonNumeric

public class FilterIterator
extends Object
implements SequenceIterator

A FilterIterator filters an input sequence using a filter expression. Note that a FilterIterator is not used where the filter is a constant number (PositionFilter is used for this purpose instead), so this class does no optimizations for numeric predicates.

Nested Class Summary

static class

FilterIterator.NonNumeric Subclass to handle the common special case where it is statically known that the filter cannot return a numeric value

Field Summary

protected SequenceIterator	base
protected Expression	filter
protected XPathContext	filterContext

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

GROUNDED, LAST_POSITION_FINDER, LOOKAHEAD

Constructor Summary

FilterIterator(SequenceIterator base, Expression filter, XPathContext context)
Constructor

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 iterator to return the same nodes
protected Item	getNextMatchingItem() Get the next item in the base sequence that matches the filter predicate if there is such an item, or null if not.
int	getProperties() Get properties of this iterator, as a bit-significant integer.
protected boolean	matches() Determine whether the context item matches the filter predicate
Item	next() Get the next item if there is one
int	position() Get the current position.

Methods inherited from class java.lang.Object

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

Field Detail

base

protected SequenceIterator base

filter

protected Expression filter

filterContext

protected XPathContext filterContext

Constructor Detail

FilterIterator

public FilterIterator(SequenceIterator base,
                      Expression filter,
                      XPathContext context)

Constructor

Parameters:

base - An iteration of the items to be filtered

filter - The expression defining the filter predicate

context - The context in which the expression is being evaluated

Method Detail

next

public Item next()
          throws XPathException

Get the next item if there is one

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

getNextMatchingItem

protected Item getNextMatchingItem()
                            throws XPathException

Get the next item in the base sequence that matches the filter predicate if there is such an item, or null if not.

Returns:

the next item that matches the predicate

Throws:

XPathException

matches

protected boolean matches()
                   throws XPathException

Determine whether the context item matches the filter predicate

Returns:

true if the context item matches

Throws:

XPathException

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

Get another iterator to return the same nodes

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.