Taking the mapper apart
Sunday, February 28, 2010
8:51 PM
Taking the mapper apart: 
public void map(WritableComparable key, Writable value,
  OutputCollector<Text, IntWritable> output, Reporter reporter)
WritableComparable: 
an interface requiring support for set, <, ==, >. 
Writable: 
an interface requiring support for just set. 
(WritableComparable extends Writable)
OutputCollector: 
a place to put output from the mapping process, e.g., via
output.collect(word, one)
Reporter: 
a way to communicate problems to the user.  