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import java.io.IOException;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

// Define the SortStudNames class that contains the MapReduce job configuration
public class SortStudNames {

    // Mapper class that defines the map operation
    public static class SortMapper extends Mapper<LongWritable, Text, Text, Text> {
        @Override
        protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
            // Split the input line by comma
            String[] token = value.toString().split(",");
            // Write the student name as key, and a composite value (ID-name) as value
            context.write(new Text(token[1]), new Text(token[0] + "-" + token[1]));
        }
    }

    // Reducer class that defines the reduce operation
    public static class SortReducer extends Reducer<Text, Text, NullWritable, Text> {
        @Override
        public void reduce(Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException {
            // For each value in the list of values for the same key, write it to the context
            for (Text details : values) {
                context.write(NullWritable.get(), details);
            }
        }
    }

    // Main method to configure and submit the MapReduce job
    public static void main(String[] args) throws IOException, InterruptedException, ClassNotFoundException {
        Configuration conf = new Configuration();
        Job job = new Job(conf, "SortStudNames");
        
        job.setJarByClass(SortStudNames.class);
        job.setMapperClass(SortMapper.class);
        job.setReducerClass(SortReducer.class);
        
        // Set the types of the output key and value
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(Text.class);
        
        // Set the input and output paths (taken from command line arguments for flexibility)
        FileInputFormat.setInputPaths(job, new Path(args[0]));    
        FileOutputFormat.setOutputPath(job, new Path(args[1]));     
        
        // Exit with a success or failure notification
        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }
}
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