Java isNan how it works?
floating-point, java, nan
Solution
That method can return true for certain operations, for example:
System.out.println(Float.isNaN(0.0f / 0.0f));
System.out.println(Double.isNaN(Math.sqrt(-1)));
Basically, `NaN` represents an undefined value. The value of `0.0 / 0.0` is `NaN`, and `Nan != NaN`. It may seem logical because `Math.sqrt(-1)` also gives you `NaN`.
See the javadoc of `Double.NaN`:
It is equivalent to the value returned by `Double.longBitsToDouble(0x7ff8000000000000L)`
And then `Double.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`. No IEEE 754 floating-point operation provided by Java can distinguish between two NaN values of the same type with different bit patterns.
Problem
I was looking at the `openjdk-1.7.0_25` source code and I have seen this method: ``` /** * Returns {@code true} if the specified number is a * Not-a-Number (NaN) value, {@code false} otherwise. * * @param v the value to be tested. * @return {@code true} if the argument is NaN; * {@code false} otherwise. */ static public boolean isNaN(float v) { return (v != v); } ``` I can't understand how it works, when this method can return `true`?