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    
019    package org.apache.hadoop.mapreduce.lib.aggregate;
020    
021    import java.util.ArrayList;
022    
023    import org.apache.hadoop.classification.InterfaceAudience;
024    import 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
032    public 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    }