001/*
002 * Copyright (c) 2016-2017 Chris K Wensel <chris@wensel.net>. All Rights Reserved.
003 * Copyright (c) 2007-2017 Xplenty, Inc. All Rights Reserved.
004 *
005 * Project and contact information: http://www.cascading.org/
006 *
007 * This file is part of the Cascading project.
008 *
009 * Licensed under the Apache License, Version 2.0 (the "License");
010 * you may not use this file except in compliance with the License.
011 * You may obtain a copy of the License at
012 *
013 *     http://www.apache.org/licenses/LICENSE-2.0
014 *
015 * Unless required by applicable law or agreed to in writing, software
016 * distributed under the License is distributed on an "AS IS" BASIS,
017 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
018 * See the License for the specific language governing permissions and
019 * limitations under the License.
020 */
021
022package cascading.pipe.joiner;
023
024import java.io.Serializable;
025import java.util.Iterator;
026
027import cascading.tuple.Tuple;
028
029/**
030 * Interface Joiner allows for custom join strategies against a {@link cascading.pipe.CoGroup}.
031 * <p>
032 * Joins perform based on the equality of the join keys. In the case of null values, Java treats two
033 * null values as equivalent. SQL does not treat null values as equal. To produce SQL like results in a given
034 * join, a new {@link java.util.Comparator} will need to be used on the joined values to prevent null from
035 * equaling null. As a convenience, see the {@link cascading.util.NullNotEquivalentComparator} class.
036 */
037public interface Joiner extends Serializable
038  {
039  /**
040   * Returns an iterator that joins the given CoGroupClosure co-groups.
041   *
042   * @param closure of type GroupClosure
043   * @return an iterator
044   */
045  Iterator<Tuple> getIterator( JoinerClosure closure );
046
047  /**
048   * Returns the number of joins this instance can handle. A value of -1 denotes there is no limit.
049   *
050   * @return an int
051   */
052  int numJoins();
053  }