Upper year CS major here. I'd say start with whatever you feel comfortable with. Some will say you have to start with Big Java: Early Objects and read every word, others will say you must start with C/C++ or python if they're more lax. Personally, I think all you really need is a project to keep you motivated to learn. Whether it be a website for yourself to display your resume and achievements, a simple game that you create, or just an everyday utility tool that you have found a use case for.
Stay motivated! And use a project you are interested in to facilitate your learning.