Actually back in 2012 Java wasn't that popular. Here's the language stats for the 200 teams 1.5 years ago:

  Ruby 28.4%  
  Python 27.5%
  Clojure 10.1%
  Java 9.2%
  CoffeeScript 8.3%
  Haskell 6.4%
  JavaScript 5.5%
  Scala 1.8%
  Go 1.8%
  Groovy 0.9%

This year Java rise and Ruby's drop are quite obvious when compared to the old stats.