Dev Nexus 2019 – Java Puzzlers NG S04 – JFrog

See the table of contents for my other blog posts from the conference

Baruch Sadogursky @jbaruch and Viktor Gamov @gamussa

#javapuzzlersng #devnexus


  • Java Puzzlers – 2001 at Oracle Open World. Did many years in a row
  • For later versions of Java
  • Slides with all answers at


  • Only a handful of people on Java 11.
  • Most people on Java 8
  • Unsurprisingly, hardly anyone on non-LTS versions

Note: they requested not posting the answers (even though they are online).


  • If you have an instance variable does This.this.this or this.this compile?

Fun facts that are not the answers

  • Can use non-English characters

How I did/observations

I got 33% (3/9) right. Well, slightly better than guessing randomly :).

  1. I was one of two people to get the first one right! It helps knowing it is a puzzler. I would have guessed compile otherwise!
  2. A lot of people including me got this right. It turns out a new an obscure bit of trivia that showed up in the question but wasn’t relevant to answer it. Fun!
  3. First one I got wrong. That was subtle!
  4. I got this wrong again. I knew the first trick, but not the second. Damn, the compiler is smart!
  5. Three wrong in a row. Again, I saw the first trick, but not the second.
  6. Fourth wrong in a row. Definitely a WTF moment for the answer! (These are great)
  7. Fifth wrong. “Good distribution of answers” – does that mean people voted randomly?
  8. Finally got one right after a while
  9. Ooh a Java 10 one! None of the tricks I could think of in this space are in the question. (Got it wrong of course)

My take

This was fun. They are great showman, have good rapport and had really obscure interesting puzzlers. I also like the showed docs for some of the obscure stuff.

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