The Wikipedia page about operator precedence explains Javaluator uses the standard operator precedence (-2^2=-4). Excel or bash shell script use another convention where -2^2=4. This can be set using the DoubleEvaluator.Style class in version 1.2.1. Support is available through the tickets and the discussion tabs.
Works great, but it is hard to get help. Maby the javaluator should have had a forum? Minor bug however: -2^2 = -4 (-2)^2 = 4