java - Java 变量如何与自身不同？

Question

我想知道这个问题是否可以用 Java 解决(我是该语言的新手)。这是代码:

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");
        }
    }
}

我在实验室收到了以下问题:如何在不修改条件本身的情况下跳过第一种情况(即使 x == x 条件为假)？

Answer 1

一种简单的方法是使用 Float.NaN :

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

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

Not ok

你可以用 Double.NaN 做同样的事情.

---

来自 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.

...