Re: Comparing floating point values in Java

Arne Vajhøj wrote:
Philipp wrote:
I'm aware of problems (rounding, NaN etc) when comparing floating point values in computers.
In C++ this goes a bit further as you cannot compare with certitude floating point numbers even if you have made exactly the same operations on each of them (see eg: http://www.parashift.com/c++-faq-lite/newbie.html#faq-29.18 )

My question: In Java, will unchanged values compare strictly true if equal?
Is it _guaranteed_ that the following code does output "true" on all JVMs?

example code:
public class Test {
public static void main(String[] args) {
float a = 1;
float b = 1;
System.out.println("a == b?: " + (a == b));
}
}

Your example is not equivalent to the example in your link.

Yes I'm aware of that. The point in the link is that compiler optimization can lead to unequal floats even if exactly the same operations were performed on it. Is this also true for Java?

But in general you should not use == to compare floating
points in Java either.

Agree

Your example are just more simple than real life code.

No! (If I ask the question it's because I met this problem)

I was calculating an array of float values from some user input. But sometimes (rarely) the calculation cannot be done (this is correct behavior).
I then want to mark these values by setting them to -1 and treat this special case later on. So I later need to test for -1 in my array.

Philipp
.

Relevant Pages

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