How can a Java variable be different from itself? [duplicate]

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?

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.

...

int x = 0;
if (x == x) {
    System.out.println("Not ok");
} else {
    System.out.println("Ok");
}

By the Java Language Specifications NaN is not equal to NaN.

Therefore any line that caused x to be equal to NaN would cause this, such as

double x=Math.sqrt(-1);

From the Java Language Specifications:

Floating-point operators produce no exceptions (§11). An operation that overflows produces a signed infinity, an operation that underflows produces a denormalized value or a signed zero, and an operation that has no mathematically definite result produces NaN. All numeric operations with NaN as an operand produce NaN as a result. As has already been described, NaN is unordered, so a numeric comparison operation involving one or two NaNs returns false and any != comparison involving NaN returns true, including x!=x when x is NaN.

Not sure if this is an option but changing x from local variable to a field would allow other thread to change its value between the reading left and right side in if statement.

Here is short demo:

class Test {

    static int x = 0;

    public static void main(String[] args) throws Exception {

        Thread t = new Thread(new Change());
        t.setDaemon(true);
        t.start();

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

class Change implements Runnable {
    public void run() {
        while (true)
            Test.x++;
    }
}

Output:

⋮
Ok
Ok
Ok
Ok
Ok
Ok
Ok
Ok
Not ok