Is there an Java API viewer on command line like man for c and ri for ruby?

Is there an Java API viewer on command line?

I have been using man for C programming and ri for Ruby programming. Both of them seems very convenient for me, and now I am looking for something alike for Java API.

I apologize if this question has been raised before. I did many Google searches but no result shows up. I think I might have been using the wrong terms.