/** * Copyright 2005 The Apache Software Foundation * * Licensed 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.mapred.lib;import java.io.IOException;import java.util.Iterator;import org.apache.hadoop.mapred.Reducer;import org.apache.hadoop.mapred.OutputCollector;import org.apache.hadoop.mapred.Reporter;import org.apache.hadoop.mapred.MapReduceBase;import org.apache.hadoop.io.WritableComparable;import org.apache.hadoop.io.LongWritable;/** A {@link Reducer} that sums long values. */public class LongSumReducer extends MapReduceBase implements Reducer {  public void reduce(WritableComparable key, Iterator values,                     OutputCollector output, Reporter reporter)    throws IOException {    // sum all values for this key    long sum = 0;    while (values.hasNext()) {      sum += ((LongWritable)values.next()).get();    }    // output sum    output.collect(key, new LongWritable(sum));  }}