net.sf.saxon.om

Class MemoSequence<T extends Item<?>>

java.lang.Object

net.sf.saxon.om.MemoSequence<T>

All Implemented Interfaces:

Sequence<T>

public class MemoSequence<T extends Item<?>>
extends java.lang.Object
implements Sequence<T>

A Sequence implementation that represents a lazy evaluation of a supplied iterator. Items are read from the base iterator only when they are first required, and are then remembered within the local storage of the MemoSequence, which eventually (if the sequence is read to the end) contains the entire value.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
class	MemoSequence.ProgressiveIterator A ProgressiveIterator starts by reading any items already held in the reservoir; when the reservoir is exhausted, it reads further items from the inputIterator, copying them into the reservoir as they are read.

Field Summary

Fields

Modifier and Type	Field and Description
protected static int	EMPTY
protected int	state

Constructor Summary

Constructors

Constructor and Description
MemoSequence(SequenceIterator<T> iterator)

Method Summary

Modifier and Type	Method and Description
T	head() Get the first item in the sequence.
Item	itemAt(int n) Get the Nth item in the sequence (0-based), reading new items into the internal reservoir if necessary
SequenceIterator<T>	iterate() Get a SequenceIterator over all the items in the sequence

Methods inherited from class java.lang.Object

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

Methods inherited from interface net.sf.saxon.om.Sequence

asIterable, makeRepeatable, materialize

Field Detail

state

protected int state

EMPTY

protected static final int EMPTY

See Also:

Constant Field Values

Constructor Detail

MemoSequence

public MemoSequence(SequenceIterator<T> iterator)

Method Detail

head

public T head()
       throws XPathException

Description copied from interface: Sequence

Get the first item in the sequence.

Specified by:

head in interface Sequence<T extends Item<?>>

Returns:

the first item in the sequence if there is one, or null if the sequence is empty

Throws:

XPathException - in the situation where the sequence is evaluated lazily, and evaluation of the first item causes a dynamic error.

iterate

public SequenceIterator<T> iterate()
                            throws XPathException

Description copied from interface: Sequence

Get a SequenceIterator over all the items in the sequence

Specified by:

iterate in interface Sequence<T extends Item<?>>

Returns:

an iterator (specifically, a Saxon SequenceIterator, which is not a Iterator) over all the items

Throws:

XPathException - in the situation where the sequence is evaluated lazily, and constructing an iterator over the items causes a dynamic error.

itemAt

public Item itemAt(int n)
            throws XPathException

Get the Nth item in the sequence (0-based), reading new items into the internal reservoir if necessary

Parameters:

n - the index of the required item

Returns:

the Nth item if it exists, or null otherwise

Throws:

XPathException - if the input sequence cannot be read