Java isNan how it works?

Question

I was looking at the openjdk-1.7.0_25 source code and I have seen this method:

/**
 * Returns {@code true} if the specified number is a
 * Not-a-Num         


        

Answer 1

Simple.. Nan is always != NaN, these values are not equal to anything. See this:

As has already been described, NaN is unordered, so a numeric comparison operation involving one or two NaNs returns false and any != comparison involving NaN returns true, including x!=x when x is NaN.

So testing if v != v is sufficient to tell whether the value is NaN or not.