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.operation; 022 023import cascading.tuple.Fields; 024import cascading.tuple.TupleEntry; 025import cascading.tuple.TupleEntryCollector; 026 027/** 028 * Interface AggregatorCall provides access to the current {@link Aggregator} invocation arguments. 029 * <p/> 030 * This interface is generic, allowing the user to set a custom 'context' object when {@link Aggregator#start(cascading.flow.FlowProcess, AggregatorCall)} 031 * is called. The {@link OperationCall#setContext(Object)} and {@link OperationCall#getContext()} methods are 032 * inherited from {@link OperationCall}. 033 * 034 * @see Aggregator 035 * @see OperationCall 036 */ 037public interface AggregatorCall<C> extends OperationCall<C> 038 { 039 /** 040 * Returns the current grouping {@link TupleEntry}. 041 * 042 * @return TupleEntry 043 */ 044 TupleEntry getGroup(); 045 046 /** 047 * Returns {@link TupleEntry} of argument values. 048 * <p/> 049 * Will return {@code null} unless called in {@link Aggregator#aggregate(cascading.flow.FlowProcess, AggregatorCall)}. 050 * <p/> 051 * Note that the returned TupleEntry should not be cached (stored in a Collection), nor should the underlying Tuple 052 * instance. Where possible Cascading will re-use both TupleEntry and Tuple instances. 053 * <p/> 054 * To get a safe copy that can be cached, use {@link TupleEntry#getTupleCopy()}. 055 * 056 * @return TupleEntry 057 */ 058 TupleEntry getArguments(); 059 060 /** 061 * Return the resolved {@link cascading.tuple.Fields} declared by the current {@link Operation}. 062 * 063 * @return Fields 064 */ 065 Fields getDeclaredFields(); 066 067 /** 068 * Returns the {@link cascading.tuple.TupleEntryCollector} used to emit result values. 069 * <p/> 070 * Will return {@code null} unless called in {@link Aggregator#complete(cascading.flow.FlowProcess, AggregatorCall)}. 071 * 072 * @return TupleCollector 073 */ 074 TupleEntryCollector getOutputCollector(); 075 }