net.sf.saxon.expr

Class SubsequenceIterator

java.lang.Object

net.sf.saxon.expr.SubsequenceIterator

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable, LastPositionFinder, SequenceIterator, LookaheadIterator

public class SubsequenceIterator
extends java.lang.Object
implements SequenceIterator, LastPositionFinder, LookaheadIterator

A SubsequenceIterator selects a subsequence of a sequence

Method Summary

Modifier and Type	Method and Description
void	close() Close the iterator.
void	discharge() Calling this method instructs the iterator to release any resources it holds, while still remaining able to deliver the remaining items in the sequence.
int	getLength() Get the last position (that is, the number of items in the sequence).
boolean	hasNext() Test whether there are any more items available in the sequence
static SequenceIterator	make(SequenceIterator base, int min, int max) Static factory method.
Item	next() Get the next item if there is one
boolean	supportsGetLength() Ask whether this iterator supports use of the 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

Method Detail

make

public static SequenceIterator make(SequenceIterator base,
                                    int min,
                                    int max)
                             throws XPathException

Static factory method. Creates a SubsequenceIterator, unless for example the base Iterator is an ArrayIterator, in which case it optimizes by creating a new ArrayIterator directly over the underlying array. This optimization is important when doing recursion over a node-set using repeated calls of $nodes[position()>1]

Parameters:

base - An iteration of the items to be filtered

min - The position of the first item to be included (base 1)

max - The position of the last item to be included (base 1)

Returns:

an iterator over the requested subsequence

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()

Test whether there are any more items available in the sequence

Specified by:

hasNext in interface LookaheadIterator

Returns:

true if there are more items in the sequence

next

public Item next()

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.

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.

Specified by:

close in interface java.io.Closeable

Specified by:

close in interface java.lang.AutoCloseable

Specified by:

close in interface SequenceIterator

discharge

public void discharge()

Description copied from interface: SequenceIterator

Calling this method instructs the iterator to release any resources it holds, while still remaining able to deliver the remaining items in the sequence. This may require the iterator to calculate the rest of the sequence eagerly. The method is called by a client if it anticipates that it might not read the iterator to completion, but it cannot guarantee that SequenceIterator.close() will be called when no more items are needed.

Specified by:

discharge in interface SequenceIterator

supportsGetLength

public boolean supportsGetLength()

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

Specified by:

supportsGetLength in interface LastPositionFinder

Returns:

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

getLength

public int getLength()

Get the last position (that is, the number of items in the sequence).

Specified by:

getLength in interface LastPositionFinder

Returns:

the number of items in the sequence