org.apache.hadoop.mapreduce
Classes 
Counter
CounterGroup
Counters
ID
InputFormat
InputSplit
Job
JobContext
JobID
MapContext
Mapper
OutputCommitter
OutputFormat
Partitioner
RecordReader
RecordWriter
ReduceContext
Reducer
StatusReporter
TaskAttemptContext
TaskAttemptID
TaskID
TaskInputOutputContext
Enums 
Job.JobState