Is there any excuse not to know Java?
mark_l_watson: That is a strong statement, and not true for everyone, so I would vote for it not being necessary to know Java.Until about 3 years ago, I used Common Lisp and Java each roughly 40% in my work (I still think that if you search for "Java consultant" I am the number 1 Google hit :-)However, after I started using Ruby, I have transitioned to using Ruby for most of my work.Ruby is great because it provides most of the advantages of Lisp except for the fantastic run time performance (natively compiled Common Lisp is fast!). However, for many (at least web) applications, bottlenecks tend to be stuff like session handling across multiple servers, database access, dealing with network partitioning and server failure, etc.One problem with Lisp is the lack of a super rich ecology of libraries. Lots of great stuff is available for Lisp, but still weak compared to Ruby, Java, Python, etc. I'm rewriting a customers app right now because we learned what we needed to learn with a small Common Lisp prototype, and are now doing a hopefully final Ruby + Rails rich UI web portal (it is so much easier to write a rich web UI in Rails that in Lisp-based alternatives).I would advise concentrating on one language and platform, and only spend perhaps 5 to 10 hours a week (an evening and some weekend time) learning new languages and frameworks.BTW, feel free to substitute Python for Ruby, in my advice to your students - pick a primary language based on which you enjoy using the most. Also, Java as your primary language is fine also, if that suits you.