The point of the article was too prove that it's hard to do Open Adressing in Java and beat HashMap performance, that uses Separate Chaining.

The article contains also a Robin Hood implementation that overall works worse than HashMap. If you can give something recommendation on how to improve it I would forever in debt.

you mean like Java? https://docs.oracle.com/en/java/javase/16/docs/api/jdk.incub...