Answer / Akhilendra Kumar Singh

"The Key and Value classes in Hadoop MapReduce have some restrictions: 1) Both keys and values must implement the interfaces Writable or comparable, as well as their respective Comparable interface (Comparable<Key> and Comparable<Value>). 2) Keys and Values should be serializable. 3) The Key class should implement the public no-arg constructor to enable Hadoop framework's deserialization of key objects.

Where is hadoop-env.sh file present?

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Which one is default?

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Name the most common input formats defined in hadoop?

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