hadoop compiling - hadoop

Question

I'm new to hadoop. I got this code from net
import java.io.IOException;
import java.util.*;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.conf.*;
import org.apache.hadoop.io.*;
import org.apache.hadoop.mapred.*;
import org.apache.hadoop.util.*;
public class Gender {
private static String genderCheck = "female";
public static class Map extends MapReduceBase implements Mapper {
private final static IntWritable one = new IntWritable(1);
private Text locText = new Text();
public void map(LongWritable key, Text value, OutputCollector output, Reporter reporter) throws IOException {
String line = value.toString();
String location = line.split(",")[14] + "," + line.split(",")[15];
long male = 0L;
long female = 0L;
if (line.split(",")[17].matches("\d+") && line.split(",")[18].matches("\d+")) {
male = Long.parseLong(line.split(",")[17]);
female = Long.parseLong(line.split(",")[18]);
}
long diff = male - female;
locText.set(location);
if (Gender.genderCheck.toLowerCase().equals("female") && diff < 0) {
output.collect(locText, new LongWritable(diff * -1L));
}
else if (Gender.genderCheck.toLowerCase().equals("male") && diff
> 0) {
output.collect(locText, new LongWritable(diff));
}
} }
public static void main(String[] args) throws Exception {
JobConf conf = new JobConf(Gender.class);
conf.setJobName("gender");
conf.setOutputKeyClass(Text.class);
conf.setOutputValueClass(LongWritable.class);
conf.setMapperClass(Map.class);
if (args.length != 3) {
System.out.println("Usage:");
System.out.println("[male/female] /path/to/2kh/files /path/to/output");
System.exit(1);
}
if (!args[0].equalsIgnoreCase("male") && !args[0].equalsIgnoreCase("female")) {
System.out.println("first argument must be male or female");
System.exit(1);
}
Gender.genderCheck = args[0];
conf.setInputFormat(TextInputFormat.class);
conf.setOutputFormat(TextOutputFormat.class);
FileInputFormat.setInputPaths(conf, new Path(args[1]));
FileOutputFormat.setOutputPath(conf, new Path(args[2]));
JobClient.runJob(conf); }
}
when I compile this code using "javac -cp /usr/local/hadoop/hadoop-core-1.0.3.jar Gender.java"
getting the following error:
"Gender.Map is not abstract and does not override abstract method
map(java.lang.Object,java.lang.Object,org.apache.hadoop.mapred.OutputCollector,org.apache.hadoop.mapred.Reporter)
in org.apache.hadoop.mapred.Mapper
public static class Map extends MapReduceBase implements Mapper "
How can I compile it correctly?

Answer 1

Change the class Maper class declaration as follows:
public static class Map extends MapReduceBase implements Mapper<LongWritable,Text,Text, LongWritable>
If you do not specify any specific class names, you would need to have the map function as follows:
#Override
public void map(Object arg0, Object arg1, OutputCollector arg2, Reporter arg3) throws IOException {
// TODO Auto-generated method stub
}
Now, the specific types denote here the expected input key-value pair types and the output key-value types from the mapper.
In your case the input key-value pair are LongWritable-Text.
And, guessing from your output.collect method calls, your mapper output key-value pair is Text-LongWritable.
Hence, your Map class shall implememnt Mapper<LongWritable,Text,Text, LongWritable>.
There was one more error in your code -
Using "\d+" will not compile as \d has no meaning, after backslash it expects a special escape sequence, so I guess for you the following should work:
line.split(",")[17].matches("\\d+")

Answer 2

Change the map class as follows:
public static class Map extends MapReduceBase implements Mapper <Input key, Input value, Output Key , Output Value>
In your case the input key is LongWritable, Input value is Text, Output Key is Text , Output value is LongWritable
public static class Map extends MapReduceBase implements Mapper <LongWritable, Text, Text,LongWritable>