What is the best way for a visitor to Dublin to get to/from Giant's Causeway in a single day?

I am considering a trip to Dublin in the near future and would love to visit Giant's Causeway. I do not plan on getting a car. I have seen guide books which give directions from Belfast, but there do not appear to be any trip planners that outline a trip from Dublin. I don't know much about the trains or other services, and would love to get a better understanding of what my options are. Thanks!