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// Copyright (c) 2013 Saxonica Limited.
// This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0.
// If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
// This Source Code Form is "Incompatible With Secondary Licenses", as defined by the Mozilla Public License, v. 2.0.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
package net.sf.saxon.om;
import net.sf.saxon.trans.XPathException;
/**
* A SequenceIterator is used to iterate over any XPath 2 sequence (of values or nodes).
* To get the next item in a sequence, call next(); if this returns null, you've
* reached the end of the sequence.
*
* A SequenceIterator keeps track of the current Item and the current position.
* The objects returned by the SequenceIterator will always be either nodes
* (class NodeInfo) or singleton values (class AtomicValue): these are represented
* collectively by the interface Item.
*
* This interface forms part of the public Saxon API. The JavaDoc "since" flag is used from
* release 8.4 onwards to indicate methods that are considered to be a stable part
* of the API. Methods without a "since" flag should not be regarded as a stable part
* of the API.
*
* Note that the stability of this interface applies to classes that use the interface,
* not to classes that implement it. The interface may be extended in future to add new methods.
*
* @author Michael H. Kay
* @since 8.4
*/
public 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().
* @throws XPathException if an error occurs retrieving the next item
* @return 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.
* @since 8.4
*/
/*@Nullable*/ public T next() throws XPathException;
/**
* 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.
*
* @return 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.
* @since 8.4
*/
/*@Nullable*/ public T current();
/**
* 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.
*
* @return 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.
*
* @since 8.4
*/
public int position();
/**
* 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.)
*
* @since 9.1
*/
public void close();
/**
* 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.
*
* @exception XPathException if any error occurs
* @return a SequenceIterator that iterates over the same items,
* positioned before the first item
* @since 8.4
*/
/*@NotNull*/
public SequenceIterator getAnother() throws XPathException;
/**
* Get properties of this iterator, as a bit-significant integer.
* @return the properties of this iterator. This will be some combination of
* properties such as {@link #GROUNDED}, {@link #LAST_POSITION_FINDER},
* and {@link #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.
* @since 8.6
*/
public int getProperties();
/**
* Property value: the iterator is "grounded". This means that (a) the
* iterator must be an instance of {@link net.sf.saxon.tree.iter.GroundedIterator}, and (b) the
* implementation of the materialize() method must be efficient (in particular,
* it should not involve the creation of new objects)
*/
public static final int GROUNDED = 1;
/**
* Property value: the iterator knows the number of items that it will deliver.
* This means that (a) the iterator must be an instance of {@link net.sf.saxon.expr.LastPositionFinder},
* and (b) the implementation of the getLastPosition() method must be efficient (in particular,
* it should take constant time, rather than time proportional to the length of the sequence)
*/
public static final int LAST_POSITION_FINDER = 1<<1;
/**
* Property value: the iterator knows whether there are more items still to come. This means
* that (a) the iterator must be an instance of {@link net.sf.saxon.tree.iter.LookaheadIterator}, and (b) the
* implementation of the hasNext() method must be efficient (more efficient than the client doing
* it)
*/
public static final int LOOKAHEAD = 1<<2;
}