What will be the result of the following code execution?

public class Main {
    public static void main(String[] args) {
        double d = Math.sqrt(-1);
        System.out.println(Double.NaN == d);
        d = d / 0;

When performing the operation, the result of which is not defined mathematically (root of a negative number, 0.0 / 0.0, etc.) returns the special value NaN (Not a Number, not a number). In the wrapper-class of fractional numbers the corresponding constants are declared: Float.NaN and Double.NaN.

A feature of value NaN is that in any arithmetic operations with it it also turns NaN, but when you try to compare it to anything with == it always gets false.

If you want to check whether a value is NaN, then you need to use the methods Float.isNaN (float) or Double.isNaN (double).

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