Why does Double.NaN==Double.NaN return false?
阿新 • • 發佈:2019-04-05
I was just studying OCPJP questions and I found this strange code:
public static void main(String a[]) { System.out.println(Double.NaN==Double.NaN); System.out.println(Double.NaN!=Double.NaN); }
When I ran the code, I got:
false true
How is the output
false
when we're comparing two things that look the same as each other? What doesNaN
mean?
NaN is by definition not equal to any number including NaN. This is part of the IEEE 754 standard and implemented by the CPU/FPU. It is not something the JVM has to add any logic to support.
http://en.wikipedia.org/wiki/NaN
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.
Java treats