001/**
002 * Copyright (c) 2011, The University of Southampton and the individual contributors.
003 * All rights reserved.
004 *
005 * Redistribution and use in source and binary forms, with or without modification,
006 * are permitted provided that the following conditions are met:
007 *
008 *   *  Redistributions of source code must retain the above copyright notice,
009 *      this list of conditions and the following disclaimer.
010 *
011 *   *  Redistributions in binary form must reproduce the above copyright notice,
012 *      this list of conditions and the following disclaimer in the documentation
013 *      and/or other materials provided with the distribution.
014 *
015 *   *  Neither the name of the University of Southampton nor the names of its
016 *      contributors may be used to endorse or promote products derived from this
017 *      software without specific prior written permission.
018 *
019 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
020 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
021 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
022 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
023 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
024 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
025 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
026 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
027 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
028 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
029 */
030package org.openimaj.util.stream.combine;
031
032import java.util.List;
033
034import org.openimaj.util.stream.AbstractStream;
035import org.openimaj.util.stream.Stream;
036
037/**
038 * Given a {@link List} of streams of a given type, present a stream of that
039 * type which asks each stream in the {@link List} for an item in turn. If any
040 * stream in the {@link List} says it has no item, this {@link Stream} will
041 * report it has no item and likely stop processing all streams. The specifics
042 * of this behaviour are that if when it comes to a stream's turn to provide an
043 * item it fails to do so, all the streams will stop being asked simultaneously.
044 * 
045 * @author Sina Samangooei (ss@ecs.soton.ac.uk)
046 * 
047 * @param <T>
048 *            Type of items in the streams being combined
049 */
050public class RoundRobinStreamCombiner<T> extends AbstractStream<T> {
051        private List<Stream<T>> streams;
052        private int currentStream;
053
054        /**
055         * Construct with the given streams. Items from each stream will be consumed
056         * in a round-robin fashion, starting with the first stream given.
057         * 
058         * @param streams
059         *            the streams to consume
060         */
061        public RoundRobinStreamCombiner(List<Stream<T>> streams) {
062                this.streams = streams;
063                this.currentStream = 0;
064        }
065
066        @Override
067        public boolean hasNext() {
068                return streams.get(currentStream).hasNext();
069        }
070
071        @Override
072        public T next() {
073                final T toRet = this.streams.get(currentStream).next();
074
075                nextStream();
076
077                return toRet;
078        }
079
080        private void nextStream() {
081                this.currentStream++;
082
083                if (this.currentStream >= streams.size())
084                        this.currentStream = 0;
085        }
086}