"A surge in interest in "big data" analytics is leading many development team managers to consider Hadoop technology. When they do, they also need to take inventory of skills available for dealing with Hadoop.
Based on Google’s MapReduce model, Hadoop distributes computing jobs and then combines results. Hadoop is Java-based, so it typically requires Java-programming abilities.
Implementing Hadoop is not the same type of Java development project that enterprise application development teams are probably used to, although effective big data analytics does share some similarity with traditional SOA -- and even batch-oriented development."
It’s not really an “either or” equation. Hadoop is written in Java. It might not be absolutely necessary to know Java, but if you are using Hadoop, it would probably be to your advantage so that you would be able to write UDFs and debug.