Re: Comparing floating point values in Java

From:

=?ISO-8859-1?Q?Arne_Vajh=F8j?= <arne@vajhoej.dk>

Newsgroups:

comp.lang.java.programmer

Date:

Sat, 30 Dec 2006 14:29:54 -0500

Message-ID:

<4596be33$0$49200$14726298@news.sunsite.dk>

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));
    }
}

Most C++ implementations use IEEE floating point.

Java uses IEEE floating point.

You should expect the same floating point issues in
Java as in C++.

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

I believe that the above should always write true in Java.

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

Your example are just more simple than real life code.

Arne