org.openrdf.sesame.sail.query.Union Maven / Gradle / Ivy
/* Sesame - Storage and Querying architecture for RDF and RDF Schema
* Copyright (C) 2001-2006 Aduna
*
* Contact:
* Aduna
* Prinses Julianaplein 14 b
* 3817 CS Amersfoort
* The Netherlands
* tel. +33 (0)33 465 99 87
* fax. +33 (0)33 465 99 87
*
* http://aduna-software.com/
* http://www.openrdf.org/
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
package org.openrdf.sesame.sail.query;
import java.io.IOException;
import org.openrdf.sesame.sail.RdfSource;
/**
* Determines the union of two sets of values that are produced by queries.
*
* @author Jeen Broekstra
*/
public class Union extends SetOperator {
/**
* Creates a new Union object that reports the union of the query answers
* that are reported by both the left- and right argument.
**/
public Union(Query leftArg, Query rightArg, boolean all) {
super(leftArg, rightArg, all);
}
// implements Query.evaluate()
public void evaluate(RdfSource rdfSource, QueryAnswerListener listener)
throws SailQueryException
{
if (!_all) {
listener = new DuplicatesFilter(listener);
}
ContinueEvaluationListener cel = new ContinueEvaluationListener(listener);
_leftArg.evaluate(rdfSource, cel);
if (cel.continueEvaluation()) {
_rightArg.evaluate(rdfSource, listener);
}
}
public String toString() {
return
"(" + _leftArg.toString() +
" UNION " + (_all ? "ALL " : "") +
_rightArg.toString() + ")";
}
/*---------------------------------------+
| Inner class ContinueEvaluationListener |
+---------------------------------------*/
private static class ContinueEvaluationListener implements QueryAnswerListener {
private boolean _continueEvaluation = true;
private QueryAnswerListener _listener;
public ContinueEvaluationListener(QueryAnswerListener l) {
_listener = l;
}
public boolean queryAnswer(QueryAnswer qa)
throws IOException
{
_continueEvaluation = _listener.queryAnswer(qa);
return _continueEvaluation;
}
public void clear() {
}
public boolean continueEvaluation() {
return _continueEvaluation;
}
}
}
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