> Lisp is for working with computational ideas and expression, whereas Java is for expressing completed programs

Not my experience at all. I often use the type system to play with and shape ideas before writing any code. The type system is a very high level specification language that allows me to express complex ideas in a few type declarations. With the added benefit that my automatic assistant (the type checker) helps me ensure that I have thought about everything before writing even a single line of code. It is a wonderful way to think about concepts, ideas and the architecture before writing any code.