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.

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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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