if statement - How can a Java variable be different from itself?

Question

I am wondering if this question can be solved in Java (I'm new to the language). This is the code:

class Condition {
    // you can change in the main
    public static void main(String[] args) { 
        int x = 0;
        if (x == x) {
            System.out.println("Ok");
        } else {
            System.out.println("Not ok");
        }
    }
}

I received the following question in my lab: How can you skip the first case (i.e. make the x == x condition false) without modifying the condition itself?

Answer 1

One simple way is to use Float.NaN:

float x = Float.NaN;  // <--

if (x == x) {
    System.out.println("Ok");
} else {
    System.out.println("Not ok");
}

Not ok

You can do the same with Double.NaN.

---

From JLS §15.21.1. Numerical Equality Operators == and !=:

Floating-point equality testing is performed in accordance with the rules of the IEEE 754 standard:

• If either operand is NaN, then the result of == is false but the result of != is true.

  Indeed, the test x!=x is true if and only if the value of x is NaN.

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