The process in which a relatively unspecialized cell acquires the characteristics of a mature hemocyte. Hemocytes are blood cells associated with a hemocoel (the cavity containing most of the major organs of the arthropod body) which are involved in defense and clotting of hemolymph, but not involved in transport of oxygen. [ GOC:jl GOC:mtg_sensu http://purl.obolibrary.org/obo/CL_0000387 http://www.ncbi.nlm.nih.gov/pubmed/9550723 ]