Might not be Java but still interesting, it made me think of one of my favorite little quirks in C++:

  #include <cmath>
  
  //Floating point model: Strict:Precise:Fast
  //Will code execute
  float a = nanf("");
  if (a == a)//S:No P:No F:Yes
      (do something);

  if (a != a)//S:Yes P:Yes F:No
      (do something);

  if (a < 0.f || a > 2.f)//S:No P:No F:Yes
      (do something);

  if (isnan(a))//S:Yes P:Yes F:Yes
      (do something);

NaN's (Not A Number) can propagate a long way through your code, possibly reaching places where they cause real problems. When dealing with input, especially networking, one should always check for NaN's. Basically the rule with NaN's is: The comparison always returns false if any NaN is involved. But as you can see; specifying the fast model throws that out of the window. (Code was otherwise unoptimized.)

In the third statement an otherwise fine check is done to make sure the value in a is sane, it doesn't get changed but its certainly not what you'd want it to be.

Whole lots of fun can be had when serving this to game servers. :D