001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019package org.apache.hadoop.mapreduce.lib.aggregate;
020
021import java.util.ArrayList;
022
023import org.apache.hadoop.classification.InterfaceAudience;
024import org.apache.hadoop.classification.InterfaceStability;
025
026/**
027 * This interface defines the minimal protocol for value aggregators.
028 * 
029 */
030@InterfaceAudience.Public
031@InterfaceStability.Stable
032public interface ValueAggregator<E> {
033
034  /**
035   * add a value to the aggregator
036   * 
037   * @param val the value to be added
038   */
039  public void addNextValue(Object val);
040
041  /**
042   * reset the aggregator
043   *
044   */
045  public void reset();
046
047  /**
048   * @return the string representation of the agregator
049   */
050  public String getReport();
051
052  /**
053   * 
054   * @return an array of values as the outputs of the combiner.
055   */
056  public ArrayList<E> getCombinerOutput();
057
058}