net.sf.saxon.expr

Class ItemMappingIterator<F extends Item,T extends Item>

java.lang.Object

net.sf.saxon.expr.ItemMappingIterator<F,T>

All Implemented Interfaces:

LastPositionFinder<T>, SequenceIterator<T>, LookaheadIterator<T>

public final class ItemMappingIterator<F extends Item,T extends Item>
extends Object
implements SequenceIterator<T>, LookaheadIterator<T>, LastPositionFinder<T>

ItemMappingIterator applies a mapping function to each item in a sequence. The mapping function either returns a single item, or null (representing an empty sequence).

This is a specialization of the more general MappingIterator class, for use in cases where a single input item never maps to a sequence of more than one output item.

Field Summary

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

GROUNDED, LAST_POSITION_FINDER, LOOKAHEAD

Constructor Summary

Constructors

Constructor and Description
ItemMappingIterator(SequenceIterator<F> base, ItemMappingFunction<F,T> action) Construct an ItemMappingIterator that will apply a specified DummyItemMappingFunction to each Item returned by the base iterator.
ItemMappingIterator(SequenceIterator<F> base, ItemMappingFunction<F,T> action, boolean oneToOne) Construct an ItemMappingIterator that will apply a specified DummyItemMappingFunction to each Item returned by the base iterator.

Method Summary

Methods

Modifier and Type	Method and Description
void	close() Close the iterator.
T	current() Get the current value in the sequence (the one returned by the most recent call on next()).
SequenceIterator<T>	getAnother() Get another SequenceIterator that iterates over the same items as the original, but which is repositioned at the start of the sequence.
int	getLength() 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.
boolean	isOneToOne() Ask whether this ItemMappingIterator is one-to-one: that is, for every input item, there is always exactly one output item.
T	next() Get the next item in the sequence.
int	position() Get the current position.
void	setOneToOne(boolean oneToOne) Say whether this ItemMappingIterator is one-to-one: that is, for every input item, there is always exactly one output item.

Methods inherited from class java.lang.Object

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

Constructor Detail

ItemMappingIterator

public ItemMappingIterator(SequenceIterator<F> base,
                   ItemMappingFunction<F,T> action)

Construct an ItemMappingIterator that will apply a specified DummyItemMappingFunction to each Item returned by the base iterator.

Parameters:

base - the base iterator

action - the mapping function to be applied.

ItemMappingIterator

public ItemMappingIterator(SequenceIterator<F> base,
                   ItemMappingFunction<F,T> action,
                   boolean oneToOne)

Construct an ItemMappingIterator that will apply a specified DummyItemMappingFunction to each Item returned by the base iterator.

Parameters:

base - the base iterator

action - the mapping function to be applied

oneToOne - true if this iterator is one-to-one

Method Detail

setOneToOne

public void setOneToOne(boolean oneToOne)

Say whether this ItemMappingIterator is one-to-one: that is, for every input item, there is always exactly one output item. The default is false.

Parameters:

oneToOne - true if this iterator is one-to-one

isOneToOne

public boolean isOneToOne()

Ask whether this ItemMappingIterator is one-to-one: that is, for every input item, there is always exactly one output item. The default is false.

Returns:

true if this iterator is one-to-one

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 getProperties() on the iterator includes the bit setting SequenceIterator.LOOKAHEAD

Specified by:

hasNext in interface LookaheadIterator<T extends Item>

Returns:

true if there are more items in the sequence

next

public T 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<T extends Item>

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 T 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<T extends Item>

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<T extends Item>

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<T extends Item>

getAnother

public SequenceIterator<T> 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.

Some implementations of this method may regenerate the input sequence, creating new nodes with different identity from the original. This is not recommended, but is hard to prevent. This causes no problem for the primary usage of this method to support the last() function, but it has been known to cause trouble in other situations.

Specified by:

getAnother in interface SequenceIterator<T extends Item>

Returns:

a SequenceIterator that iterates over the same items, positioned before the first item

Throws:

XPathException - if any error occurs

getLength

public int getLength()
              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:

getLength in interface LastPositionFinder<T extends Item>

Returns:

the number of items in the sequence

Throws:

XPathException - if an error occurs evaluating the sequence in order to determine the number of items

getProperties

public int getProperties()

Get properties of this iterator, as a bit-significant integer.

Specified by:

getProperties in interface SequenceIterator<T extends Item>

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.