Question

What was Hadoop written in?

Answer 1

The Hadoop framework is mostly written in the Java programming language, with some part of the code in C and command line utilities written as shell scripts. 

Java is a high-level, class-based, object-oriented programming language that is designed to have as few implementation dependencies as possible.

Though MapReduce Java code is common, any programming language can be used with Hadoop Streaming to implement the map and reduce parts of the user's program.