org.apache.hadoop.io
Interfaces 
Writable
WritableComparable
WritableFactory
Classes 
ArrayWritable
BooleanWritable
BooleanWritable.Comparator
BytesWritable
BytesWritable.Comparator
CompressedWritable
DataInputBuffer
DataOutputBuffer
FloatWritable
FloatWritable.Comparator
GenericWritable
IntWritable
IntWritable.Comparator
LongWritable
LongWritable.Comparator
LongWritable.DecreasingComparator
MD5Hash
MD5Hash.Comparator
NullWritable
ObjectWritable
Text
Text.Comparator
TwoDArrayWritable
VersionedWritable
VIntWritable
VLongWritable
WritableComparator
WritableFactories
WritableName
WritableUtils
Exceptions 
VersionMismatchException