Feature suggestion: Add static equals methods to Float and Double

[Joe Darcy]

Hello 99206970363698485155,h

On 1/4/2019 3:11 PM, some-java-user-99206970363698485155 at vodafonemail.de 
wrote:
> To test whether primitive float or double values are equal according to `Float.equals` and `Double.equals` you either have to create wrapper instances for them (possible performance decrease), use the respective static `compareTo` (verbose) or have to use the appropriate methods (`floatToIntBits` / `doubleToLongBits`) (verbose and error-prone since you could confuse them with the other conversion methods).


In the context of a mathematics course, it is common to define multiple 
equivalence relations over the same set of values. For objects in Java, 
we see this in object identity under "a == b" as possibly distinct from  
"a.equals(b)". For floating-point, I've written about this years back, 
please excuse some artifacts introduced by blog conversions:

     "Notions of Floating-Point Equality"
https://blogs.oracle.com/darcy/notions-of-floating-point-equality

tl;dr it would be helpful in some contexts to have an "is-equivalent" 
test for floating-point values. When I need this, say in numerics 
regression tests, I use

     Double.compare(a, b) == 0

or a method wrapping that or an equivalent expression. This expression 
distinguishes -0.0 from +0.0, but treats all NaNs as equivalent.

If writing test vectors for a specific chip, then the semantics of which 
NaN bit pattern is returned are generally defined and a 
"doubleToRawLongBits​" notion of equality would be appropriate instead.

If a static two-argument equals method were to to added to Double, to 
avoid confusion I think it would need to be added as

public boolean equals(double a, double b) {
    return a == b;
}

say, to provide the ability to have a method reference to the double == 
operation.

However, I don't think it is necessary to add that method and I don't 
find a sufficiently compelling case to add "isEquivalent" at this time.

Cheers,

-Joe


>
> It would be good to provide static methods for testing for equality of the primitive values:
>
> // In Float.java
>
> public static boolean equals(float a, float b) {
> return Float.floatToIntBits(a) == Float.floatToIntBits(b);
> }
>
> // In Double.java
>
> public static boolean equals(double a, double b) {
> return Double.doubleToLongBits(a) == Double.doubleToLongBits(b);
> }
>
> This would be very convenient for developers and prevent them from writing (possibly faulty) code for this themselves.