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ARQ is a SPARQL 1.1 query engine for Apache Jena
There is a newer version: 5.2.0
/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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.
 */

package org.apache.jena.sparql.resultset;

import java.util.ArrayList ;
import java.util.List ;

import org.apache.jena.atlas.iterator.PeekIterator ;
import org.apache.jena.atlas.lib.Lib ;
import org.apache.jena.query.QuerySolution ;
import org.apache.jena.query.ResultSet ;
import org.apache.jena.rdf.model.Model ;
import org.apache.jena.sparql.core.ResultBinding ;
import org.apache.jena.sparql.engine.binding.Binding ;

/** A result set held in-memory. rewindable.  
 */

public class ResultSetMem implements org.apache.jena.query.ResultSetRewindable, ResultSetPeekable
{
    protected List rows = new ArrayList<>();
    protected List varNames = null ;

    private int rowNumber = 0 ;
    private PeekIterator iterator = null ;
    private Model model = null ;

    /** Create an in-memory result set from another one
     *
     * @param imrs2     The other QueryResultsMem object
     */
    public ResultSetMem(ResultSetMem imrs2) {
        this(imrs2, false);
    }

    /**
     * Create an in-memory result set from another one
     *
     * @param imrs2
     *            The other ResultSetMem object
     * @param takeCopy
     *            Should we copy the rows?
     */

    public ResultSetMem(ResultSetMem imrs2, boolean takeCopy) {
        varNames = imrs2.varNames;
        if ( takeCopy )
            rows.addAll(imrs2.rows);
        else
                        // Share results (not the iterator).
                        rows = imrs2.rows;
        reset();
    }

    /**
     * Create an in-memory result set from any ResultSet object. If the
     * ResultSet is an in-memory one already, then no copying is done - the
     * necessary internal datastructures are shared. This operation destroys
     * (uses up) a ResultSet object that is not an in memory one.
     */

    public ResultSetMem(ResultSet qr) {
        model = qr.getResourceModel();
        if ( qr instanceof ResultSetMem ) {
            ResultSetMem qrm = (ResultSetMem)qr;
            this.rows = qrm.rows;
            this.varNames = qrm.varNames;
        } else {
            varNames = qr.getResultVars();
            while (qr.hasNext()) {
                Binding rb = qr.nextBinding();
                rows.add(rb);
            }
        }
        reset();
    }

    /**
     * Create an in-memory result set from an array of ResulSets. It is assumed
     * that all the ResultSets from the array have the same variables.
     * 
     * @param sets
     *            the ResultSet objects to concatenate.
     */

    public ResultSetMem(ResultSet... sets) {
        varNames = sets[0].getResultVars();

        for ( ResultSet rs : sets ) {
            if ( !varNames.equals(rs.getResultVars()) )
                throw new ResultSetException("ResultSet must have the same variables.");
            if ( rs instanceof ResultSetMem )
                rows.addAll(((ResultSetMem)rs).rows);
            else
                while (rs.hasNext())
                    rows.add(rs.nextBinding());
        }
        reset();
    }

    public ResultSetMem() {
        this.varNames = new ArrayList<>();
        reset();
    }

    // -------- ResultSet interface ------------------------------
   /**
     *  @throws UnsupportedOperationException always thrown.
     */

    @Override
    public void remove() throws java.lang.UnsupportedOperationException
    {
        throw new java.lang.UnsupportedOperationException(
            Lib.className(this)+": Attempt to remove an element");
    }

    /**
     * Is there another possibility?
     */
    @Override
    public boolean hasNext() { return iterator.hasNext() ; }

    /** Moves onto the next result possibility.
     */
    
    @Override
    public QuerySolution nextSolution()  { return new ResultBinding(model, nextBinding()) ; }
    
    @Override
    public Binding nextBinding()  { rowNumber++ ; return iterator.next() ; }

    /** Moves onto the next result possibility.
     *  The returned object should be of class QuerySolution
     */

    @Override
    public QuerySolution next() { return nextSolution() ; }

    /** Reset this result set back to the beginning */
    public void rewind( ) { reset() ; }

    @Override
    public void reset() { iterator = new PeekIterator<>(rows.iterator()) ; rowNumber = 0 ; }

    /** Return the "row" number for the current iterator item
     */
    @Override
    public int getRowNumber() { return rowNumber ; }

    @Override
    public Model getResourceModel()
    {
        return model ;
    }
    
    /** Return the number of rows
     */
    @Override
    public int size() { return rows.size() ; }
    
    /** Get the variable names for the projection
     */
    @Override
    public List getResultVars() { return varNames ; }

    @Override
    public QuerySolution peek() {
        return new ResultBinding(model, peekBinding());
    }

    @Override
    public Binding peekBinding() {
        //PeekIterator.element() is the one that throws NoSuchElementException.
        return iterator.element();
    }

}