It's mostly a novelty today. Felleisen is a programming language theorist, and him writing a little Java tutorial sounds absurd.
The book itself takes you on a journey to reinvent the Visitor pattern, in a version of Java that predates generics. You can probably find a better explainer for the Visitor pattern in Java.
The book itself takes you on a journey to reinvent the Visitor pattern, in a version of Java that predates generics. You can probably find a better explainer for the Visitor pattern in Java.