What does calling the next () method return?

In the reducer, the MapReduce API provides you with an iterator over Writable values.

What does calling the next () method return?
A . It returns a reference to a different Writable object time.
B . It returns a reference to a Writable object from an object pool.
C . It returns a reference to the same Writable object each time, but populated with different data.
D . It returns a reference to a Writable object. The API leaves unspecified whether this is a reused object or a new object.
E . It returns a reference to the same Writable object if the next value is the same as the previous value, or a new Writable object otherwise.

Answer: C

Explanation:

Calling Iterator.next() will always return the SAME EXACT instance of IntWritable, with the contents of that instance replaced with the next value.

Reference: manupulating iterator in mapreduce