From Muppet Wiki
J Friends is a Sesame Street song sung by the Anything Muppets, who list their friends whose names begin with the letter J. The names include Joe, Jim, Jane, and Joan.
These singers were performed by Jerry Nelson, Jim Henson, Fran Brill and Frank Oz.
The names in the song also happen to be the names of notable people behind the scenes: Joe (Raposo), Jane (Henson), Jim (Henson) and Joan (Ganz Cooney).