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

Because only NaN compares false with itself. So it will return true when you pass NaN to the method.

A comparison with a NaN always returns an unordered result even when comparing with itself. ... The equality and inequality predicates are non-signaling so x = x returning false can be used to test if x is a quiet NaN.

Source

It not just about Java, It is also true for all languages following IEEE754 standard.

Related question : Why does Double.NaN==Double.NaN return false?