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