Wörter zählen

public static class TokenizerMapper 
   extends Mapper<Object, Text, Text, IntWritable>{
   public void map(Object key, Text value, Context context) { } }
public static class IntSumReducer 
   extends Reducer<Text,IntWritable,Text,IntWritable> {
   public void reduce(Text key, Iterable<IntWritable> values, Context context ) { } } 
 }
public static void main(String[] args) { ...
   job.setMapperClass(TokenizerMapper.class);
   job.setCombinerClass(IntSumReducer.class);
   job.setReducerClass(IntSumReducer.class);  .. }

hadoop/src/examples/org/apache/hadoop/examples/WordCount.java