java - Why does Double.NaN==Double.NaN return false? - Stack Overflow

java - Why does Double.NaN==Double.NaN return false? - Stack Overflow

NaN means Not a Number. What is not a number? Anything. You can have anything in one side and anything in the other side, so nothing guarantees that both are equals. NaN is calculated with Double.longBitsToDouble(0x7ff8000000000000L) and as you can see in the documentation of longBitsToDouble:

If the argument is any value in the range 0x7ff0000000000001L through 0x7fffffffffffffffL or in the range 0xfff0000000000001L through 0xffffffffffffffffL, the result is a NaN.

Also, NaN is logically treated inside the API.

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