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