| /** |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you under the Apache License, Version 2.0 (the |
| * "License"); you may not use this file except in compliance |
| * with the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package org.apache.hadoop.mapreduce; |
| |
| import java.io.IOException; |
| import java.util.Iterator; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.classification.InterfaceStability; |
| |
| /** |
| * The context passed to the {@link Reducer}. |
| * @param <KEYIN> the class of the input keys |
| * @param <VALUEIN> the class of the input values |
| * @param <KEYOUT> the class of the output keys |
| * @param <VALUEOUT> the class of the output values |
| */ |
| @InterfaceAudience.Public |
| @InterfaceStability.Evolving |
| public interface ReduceContext<KEYIN,VALUEIN,KEYOUT,VALUEOUT> |
| extends TaskInputOutputContext<KEYIN,VALUEIN,KEYOUT,VALUEOUT> { |
| |
| /** Start processing next unique key. */ |
| public boolean nextKey() throws IOException,InterruptedException; |
| |
| /** |
| * Iterate through the values for the current key, reusing the same value |
| * object, which is stored in the context. |
| * @return the series of values associated with the current key. All of the |
| * objects returned directly and indirectly from this method are reused. |
| */ |
| public Iterable<VALUEIN> getValues() throws IOException, InterruptedException; |
| |
| /** |
| * {@link Iterator} to iterate over values for a given group of records. |
| */ |
| interface ValueIterator<VALUEIN> extends MarkableIteratorInterface<VALUEIN> { |
| |
| /** |
| * This method is called when the reducer moves from one key to |
| * another. |
| * @throws IOException |
| */ |
| void resetBackupStore() throws IOException; |
| } |
| } |