hadoop reduce function is not excuted?

Question

I am running the mapreduce program, but I realize that although I write a reduce function, the mapreduce does not exceute it. I then try to add @Override, the error says the reduce function does not override any super methods.

Job configuration information is as below

        preProcess.setJobName("GeneProcessing program for 100 SNP");

        preProcess.setMapperClass(PreprocessMapper.class);
        preProcess.setReducerClass(PreprocessReducer.class);

        preProcess.setInputFormatClass(TextInputFormat.class);
        //setInputFormat(TextInputFormat.class);
    preProcess.setOutputFormatClass(TextOutputFormat.class);


    preProcess.setMapOutputKeyClass(Text.class);
    preProcess.setMapOutputValueClass(Text.class);  

        preProcess.setOutputKeyClass(NullWritable.class);
    preProcess.setOutputValueClass(Text.class);

    //preProcess.setNumMapTasks(4);
    preProcess.setNumReduceTasks(4);
    FileInputFormat.setInputPaths(preProcess, preprocessInputPath);
    FileOutputFormat.setOutputPath(preProcess, preprocessOutputPath);
    //JobClient.runJob(preProcess);
        preProcess.waitForCompletion(true);

Reduce code is as below

import java.io.*;
import java.util.*;


import org.apache.hadoop.io.*;
import org.apache.hadoop.mapreduce.Reducer;
    public class PreprocessReducer extends Reducer<Text, Text, NullWritable, Text> 
    {
        public Text newKey = new Text("");

            //no enter the reduce task
            @Override
        protected void reduce(Text key, Iterator<Text> values, Context output)                 
             throws IOException, InterruptedException                
            {

            do something here

        }

    }

Answer 1

Your signature for the reduce method is wrong - the second argument should be Iterable<Text> rather than Iterator<Text>:

@Override
protected void reduce(Text arg0, Iterable<Text> arg1,
         Context arg2)
         throws IOException, InterruptedException {

}

What IDE are you using? Eclipse has a Source -> Override / Implement method menu option which makes getting the signature correct much easier. I'm sure Netbeans has a similar function.