/*
* $Header$
* $Revision: 624 $
* $Date: 2006-06-24 21:02:12 +1000 (Sat, 24 Jun 2006) $
*
* ====================================================================
*
* The Apache Software License, Version 1.1
*
* Copyright (c) 2003, 2004 The JRDF Project. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. The end-user documentation included with the redistribution, if
* any, must include the following acknowlegement:
* "This product includes software developed by the
* the JRDF Project (http://jrdf.sf.net/)."
* Alternately, this acknowlegement may appear in the software itself,
* if and wherever such third-party acknowlegements normally appear.
*
* 4. The names "The JRDF Project" and "JRDF" must not be used to endorse
* or promote products derived from this software without prior written
* permission. For written permission, please contact
* newmana@users.sourceforge.net.
*
* 5. Products derived from this software may not be called "JRDF"
* nor may "JRDF" appear in their names without prior written
* permission of the JRDF Project.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the JRDF Project. For more
* information on JRDF, please see <http://jrdf.sourceforge.net/>.
*/
package org.jrdf.graph.mem;
import org.jrdf.graph.GraphElementFactory;
import org.jrdf.graph.GraphException;
import org.jrdf.graph.Triple;
import org.jrdf.util.ClosableIterator;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
/**
* An iterator that iterates over a group with a single fixed node.
* Relies on internal iterators which iterate over all entries in
* a submap, and the sets they point to.
* The thirdIndexIterator is used to indicate the current position.
* It will always be set to return the next value until it reaches
* the end of the group.
*
* @author <a href="mailto:pgearon@users.sourceforge.net">Paula Gearon</a>
* @author Andrew Newman
*/
public class OneFixedIterator implements ClosableIterator<Triple> {
/** The iterator for the second index. */
private Iterator<Map.Entry<Long,Set<Long>>> secondIndexIterator;
/** The iterator for the third index. */
private Iterator<Long> thirdIndexIterator;
/** The current element for the iterator on the second index. */
private Map.Entry<Long,Set<Long>> secondEntry;
/** The factory used to create the nodes to be returned in the triples. */
private GraphElementFactoryImpl factory;
/** The index of this iterator. Only needed for initialization and the remove method. */
private Map<Long,Map<Long,Set<Long>>> index;
/** The subIndex of this iterator. Only needed for initialization and the remove method. */
private Map<Long,Set<Long>> subIndex;
/** The fixed item. */
private Long first;
/** The offset for the index. */
private int var;
/** The current subject predicate and object, last returned from next(). Only needed by the remove method. */
private Long[] currentNodes;
/** Handles the removal of nodes */
private GraphHandler handler;
/**
* Constructor. Sets up the internal iterators.
* @throws IllegalArgumentException Must pass in a GraphElementFactory memory implementation.
*/
OneFixedIterator(Map<Long,Map<Long,Set<Long>>> newIndex, int newVar, Long newFirst,
GraphElementFactory newFactory, GraphHandler newHandler, Map<Long,Set<Long>> newSubIndex) {
if (!(newFactory instanceof GraphElementFactoryImpl)) {
throw new IllegalArgumentException("Must use the memory implementation of GraphElementFactory");
}
// store the node factory and other starting data
factory = (GraphElementFactoryImpl)newFactory;
handler = newHandler;
first = newFirst;
var = newVar;
index = newIndex;
currentNodes = null;
// initialise the iterators to empty
thirdIndexIterator = null;
secondIndexIterator = null;
// find the subIndex from the main index
subIndex = newSubIndex;
// check that data exists
if (null != subIndex) {
// now get an iterator to the sub index map
secondIndexIterator = subIndex.entrySet().iterator();
// check if there is data available - structural constraints say there should be
assert secondIndexIterator.hasNext();
}
}
/**
* Returns true if the iteration has more elements.
* @return <code>true</code> If there is an element to be read.
*/
public boolean hasNext() {
// confirm we still have an item iterator, and that it has data available
return null != thirdIndexIterator && thirdIndexIterator.hasNext() ||
null != secondIndexIterator && secondIndexIterator.hasNext();
}
/**
* Returns the next element in the iteration.
* @return the next element in the iteration.
* @throws NoSuchElementException iteration has no more elements.
*/
public Triple next() throws NoSuchElementException {
if (null == secondIndexIterator) {
throw new NoSuchElementException();
}
// move to the next position
updatePosition();
if (null == secondIndexIterator) {
throw new NoSuchElementException();
}
// get the next item
Long third = thirdIndexIterator.next();
// construct the triple
Long second = secondEntry.getKey();
// get back the nodes for these IDs and build the triple
currentNodes = new Long[]{first, second, third};
return new TripleImpl(factory, var, first, second, third);
}
/**
* Helper method to move the iterators on to the next position.
* If there is no next position then {@link #thirdIndexIterator thirdIndexIterator}
* will be set to null, telling {@link #hasNext() hasNext} to return
* <code>false</code>.
*/
private void updatePosition() {
// progress to the next item if needed
if (null == thirdIndexIterator || !thirdIndexIterator.hasNext()) {
// the current iterator been exhausted
if (!secondIndexIterator.hasNext()) {
// the subiterator has been exhausted
// tell the secondIndexIterator to finish
secondIndexIterator = null;
return;
}
// get the next entry of the sub index
secondEntry = secondIndexIterator.next();
// get an iterator to the next set from the sub index
thirdIndexIterator = secondEntry.getValue().iterator();
assert thirdIndexIterator.hasNext();
}
}
/**
* Implemented for java.util.Iterator.
*/
public void remove() {
if (null != thirdIndexIterator) {
// now remove from the other 2 indexes
try {
thirdIndexIterator.remove();
handler.remove(currentNodes);
// check if a set was cleaned out
Set<Long> subGroup = secondEntry.getValue();
if (subGroup.isEmpty()) {
// remove the entry for the set
secondIndexIterator.remove();
// check if a subindex was cleaned out
if (subIndex.isEmpty()) {
// remove the subindex
index.remove(first);
subIndex = null;
}
}
} catch (GraphException ge) {
throw new IllegalStateException(ge.getMessage());
}
} else {
throw new IllegalStateException("Next not called or beyond end of data");
}
}
/**
* Closes the iterator by freeing any resources that it current holds.
* Nothing to be done for this class.
* @return <code>true</code> indicating success.
*/
public boolean close() {
return true;
}
}