One of the more amusing bugs I had to figure out resulted from the fact that some of the autoboxed values get cached, resulting in peculiar behaviour when someone managed to reflectively change the boxed primitive value...

i.e. something like:

  Integer x = 42
  highlyQuestionableCode(x);
  println(x); // "24" WAT?

I'm a fan of JEP-500...

https://openjdk.org/jeps/500