io - Hadoop Custom Values for a key -

i tried implement custom writable instead of using intwritable. reason behind want have pair of values. in particular want achieve following: user_id;counter;length_of_messages;

the input files of following sort:

user_id;time_stamp;length_of_messages

the output files should aggregate information

user_id;counter;length_of_messages

semantically, stats of user given periond (e.g. 1 week) aggregating number of times wrote message in week, , sum of lengths of messages in week.

public class valueswritable implements writable {   private int counter;   private int durations;  public void write (dataoutput out) throws ioexception{   out.writeint(counter);   out.writeint(durations); } public void readfields(datainput in) throws ioexception{   counter = in.readint();   durations = in.readint(); }  public valueswritable read(datainput in) throws ioexception{   valueswritable v = new valueswritable();   v.readfields(in);   return v; } } 

i included class innerclass in mapreduce job class. question is: how can interface class? dataoutput , datainput? read tutorial http://developer.yahoo.com/hadoop/tutorial/module5.html#keytypes , modified example purpose. can't compile classes.

thanks directions.