I was about to write a similar comment but you wrote it a minute earlier. :) Seriously, the writing is long-winded and meandering.

To add to the summary:

"This particular trick also no longer works. As I found out while writing this article, modern JDKs do not allocate any space in a HashSet until something is added."

So.. The article might have been better organized (and edited to 1/4 length) and focused on the section, "Four one liners every Java programmer should know". Unfortunately, it'd still be a click-baity title.