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
    p         


        

Answer 1

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

Answer 2

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.

...

Answer 3

Using the same skip/change output approach from another answers:

class Condition {
    public static void main(String[] args) {
        try {
            int x = 1 / 0;
            if (x == x) {
                System.out.println("Ok");
            } else {
                System.out.println("Not ok");
            }
        } catch (Exception e) {
            System.out.println("Not ok");
        }
    }
}

Answer 4

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