[cat199]

plus:

it's common lisp. if the language spec hasn't changed, and your code works, you don't really need to change the interpreter.

[iak8god]

ABCL's interoperability with Java is not part of the CL spec, but an add-on. This can make it easy to quickly get things done in a situation where Java libraries are the best tool for the task, but at the cost of portability between CL implementations.