Re: Comparing floating point values in Java

"Daniel Pitts" <>
30 Dec 2006 10:33:25 -0800
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: )

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?

Thanks for answers. Phil

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

Look into StrictMath.

It might also be worthwhile to learn how to calculate error, and
compare signifigant figures only. If you only need a "probably equal",
then you can use a delta, eg:

public class FloatEquality {
    public static boolean areEqual(float a, float b, float delta) {
        return Math.abs(a - b) < delta;
    public static float DELTA_F = 0.00000001f;
    public static void main(String[] args) {
        float a = 1f;
        float b = 1f;
        System.out.println("a == b?: " + areEqual(a, b, DELTA_F);

Hope this helps.


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