Java Minutiae - Reflex

Pop Quiz
The following is a method from a very decent implementation of Java SE. I've substituted x and y for the actual method name and parameter type. What are the values of x and y ?

public static boolean x(y z)isNaN(float z) {
  return z != z;
}

PS - it's a reasonable method. it may take you a few minutes to come up with the answer.

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x = isNaN, y = float

It turns out that Float.NaN != Float.NaN. Weird! The same is true for Double.NAN. Since they're the only values with this property, testing for a lack of reflexivity uniquely identifies these values.

# posted by Jesse Wilson on Monday, May 04, 2009