What does this expression mean?

Question

https://code.sololearn.com/czVzb5TqCGSv/?ref=app

Can someone explain me this code ?

Answer 1

NaN means "not a number"

Double.isNaN(your Double) checks if your double is a number or not.

for example:
double a = 0.0/0.0
Double.isNaN(a) returns true because it is not a number
--> print a --> output: NaN

Double.isNaN(-1.0/0.0) returns false because it is a number
(output: - infinity)

Double.isNaN(7) --> false

double a = Double.isNaN does not work.
a tip: if a method starts with is then it returns a boolean (true or false)
isDigit(), isLetter(), ...

You can also look here:
https://www.tutorialspoint.com/java/lang/double_isnan.htm