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 }