They could be considered clever tricks because the Java type system does not seem very well suited to expressing such higher-level invariants. These excercises

They could be considered clever tricks because the Java type system does not seem very well suited to expressing such higher-level invariants. These excercises are interesting, but smarter solutions are not magically guaranteed to perform better in the real world. As for denotational semantics, you should either explain your point fully or this is nothing more than a trivial condescendig remark. [edited for grammar]