public class TestClass {
public static void equality () {
double dd = 3.5;
float ff = 3.5f;
System.out.println(String.format("dd vs ff == %b", dd==ff));
double dd2 = 3.2;
float ff2 = 3.2f;
System.out.println(String.format("dd2 vs ff2 == %b", dd2==ff2));
}
}
REPL output:
=> (idem.core.TestClass/equality)
nil
Console output:
nREPL server started on port 38698 on host 127.0.0.1 - nrepl://127.0.0.1:38698
dd vs ff == true
dd2 vs ff2 == false
We are talking about values as primitive types, not boxed values as objects:
The equals method for class Object implements the most discriminating possible
equivalence relation on objects; that is, for any non-null reference values x
and y, this method returns true if and only if x and y refer to the same object
(x == y has the value true).
=> (class (float 3.2))
java.lang.Float
=> (class (double 3.2))
java.lang.Double
Oupse... :)
Luc P.
On Fri, 23 Jan 2015 01:31:31 -0800
Mark Engelberg <[email protected]> wrote:
> On Fri, Jan 23, 2015 at 1:10 AM, Luc Prefontaine <
> [email protected]> wrote:
>
> > Agree, it's broken... in java...
> >
>
> I think it's more frustrating in Clojure than in Java, though,
> because in Java you have those big, ugly type annotations on every
> single variable, input and output, so there's really no question when
> you're working with a mixture of floats and doubles. In Clojure,
> it's much easier for this kind of thing to slip into your program
> unnoticed. Call a couple of external libraries that produce floats
> or doubles -- Clojure will happily hide the difference from you and
> then you get burned.
>
> As I frequently find myself explaining to newcomers to Clojure, one of
> Clojure's biggest weaknesses is that it goes to great pains to hide
> type details (floats vs doubles, boxed vs unboxed, hash sets vs array
> sets, etc.) and every once in a while it really matters -- a lot --
> what the types actually are and there aren't many tools for
> discovering the flow of types through your code.
>
> So I wouldn't necessarily go blaming this on Java.
>
> Furthermore, I'm not so sure it is broken in Java:
>
> => (.equals (float 2) (double 2))
> false
>
> => (.compareTo (float 2) (double 2))
> ClassCastException Cannot cast java.lang.Double to java.lang.Float
> java.lang.Class.cast (Class.java:3258)
>
> So Java doesn't appear to transparently treat floats and doubles as
> equal (which is consistent with the fact that Java's hashes of floats
> and doubles can be different).
>
--
Luc Préfontaine
SoftAddicts inc.
Québec, Canada
Mobil: (514) 993-0320
Fax: (514) 800-2017
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