I took 6.001 in the spring of 1997 and we did the simple "Decaf Java" interpreter (in Scheme). Decaf Java is an s-exp representation of a Java program's parse tree. It is foggy and distant now but I believe we did do a problem set in actual Java and then later in the semester after doing the Scheme in Scheme metacircular evaluator we did the Decaf Java interpreter. I don't have any other 6.001 experience to compare it to but I loved the version I took.