code: package it.unibz.inf.ontop.query.resultset.impl;
  
  /*
   * #%L
   * ontop-reformulation-core
   * %%
   * Copyright (C) 2009 - 2014 Free University of Bozen-Bolzano
   * %%
   * Licensed under the Apache License, Version 2.0 (the "License");
   * you may not use this file except in compliance with the License.
   * You may obtain a copy of the License at
   *
   *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   * #L%
   */
  
  import com.google.common.collect.ImmutableList;
  import it.unibz.inf.ontop.answering.logging.QueryLogger;
  import it.unibz.inf.ontop.query.resultset.OntopBindingSet;
  import it.unibz.inf.ontop.query.resultset.TupleResultSet;
  import it.unibz.inf.ontop.model.term.Variable;
  import it.unibz.inf.ontop.utils.ImmutableCollectors;
  
  import java.util.List;
  import java.util.NoSuchElementException;
  
  public class EmptyTupleResultSet implements TupleResultSet {
  
  	private final ImmutableList<String> signature;
  	private final QueryLogger queryLogger;
  	private boolean hasNextCalled = false;
  
  	public EmptyTupleResultSet(ImmutableList<Variable> answerVariables,
  							   QueryLogger queryLogger) {
  		this.signature = answerVariables.stream()
  				.map(Variable::getName)
  				.collect(ImmutableCollectors.toList());
  
  		this.queryLogger = queryLogger;
  	}
  
  	@Override
  	public void close() {
  	}
  
  	@Override
  	public int getColumnCount()  {
  		return signature.size();
  	}
  
  	@Override
  	public boolean isConnectionAlive() {
  		return false;
  	}
  
  	@Override
  	public OntopBindingSet next() {
  		throw new NoSuchElementException();
  	}
  
  	@Override
  	public List<String> getSignature() {
  		return signature;
  	}
  
  	@Override
  	public boolean hasNext()  {
  		if (!hasNextCalled)
  			queryLogger.declareLastResultRetrievedAndSerialize(0);
  		hasNextCalled = true;
  		return false;
  	}
  
  }
  