Re: Comparing floating point values in Java

From:

Patricia Shanahan <pats@acm.org>

Newsgroups:

comp.lang.java.programmer

Date:

Sun, 31 Dec 2006 00:11:38 GMT

Message-ID:

<_eDlh.8898$X72.5952@newsread3.news.pas.earthlink.net>

Daniel Pitts wrote:

Eric Sosman wrote:

Philipp wrote:

[...]

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.

Perhaps you can avoid the entire issue by choosing a
different "distinguished value." Float.NaN, maybe, using
the Float.isNaN(float) method instead of an == test. (NaN
seems a more natural surrogate for "does not compute," too.)

--
Eric Sosman
esosman@acm-dot-org.invalid

Or even have a seperate boolean array to specify valid results.
Having a magic value isn't generally a good idea, although NaN would be
the way to go if you did.

Since the special cases are rare, one could also describe them by having
e.g. a HashSet<Integer> containing the index values of the special cases.

Using any magic value, including NaN, has the risk that a bug elsewhere
in the code will get hidden as the special case. The risk can be reduced
by using a specific NaN value and Float.floatToRawIntBits to check for it.

Patricia