Helper classes

Zhong Yu zhong.j.yu at
Mon Apr 15 15:01:56 PDT 2013

Also there's another design possibility: a vacuous interface,
containing no abstract methods, but all default methods, for example

    public interface Math
        int max(int, int)

as contrast to the traditional way: a vacuous class, not a template
for objects, but only as a namespace hosting static methods.

Zhong Yu

On Mon, Apr 15, 2013 at 4:23 PM, Sam Pullara <spullara at> wrote:
> I don't feel like we would be having this discussion if Java always
> had statics in interfaces. It is the obvious place to put helpers that
> are factories and other cases that do not act directly on the
> interface type. So much so that people often put an inner class in the
> interface just to get some semblance of this behavior.
> Sam
> On Apr 15, 2013, at 1:59 PM, Luc Duponcheel <luc.duponcheel at> wrote:
>> Hello,
>> Here is my opinion on this:
>> Functionality naturally belongs to interface, say Zyx, if one of it's
>> parameters is of type Zyx
>> (and if an argument passed to it is, naturally, eagerly evaluated).
>> Other functionality naturally belongs to helper class. say Zyxs (or
>> ZyxStatics for that matter).
>> for example:
>> - transforming an element to a singleton list containing it naturally
>> belongs to the helper class
>> - joining a list of lists naturally belongs to the helper class
>> On the other hand it is sometimes useful to have static versions of methods
>> in Zyx in Zyxs because they can naturally be used as method references.
>> About discoverability:
>> When, for example, working with lists, I hope that there will be zipper
>> functionaity transforming a tuple of lists into a list of tuples. That
>> functionality naturally fits in the interface Zyx (maybe with a copy in the
>> class Zyxs). I also hope that there will be unzipper functionality
>> transforming a list of tuples into a tuple of lists. That functionality
>> naturally fits in the class Zyxs. So, if you know what method you are
>> looking for (also in terms of its signature) you often know where to look
>> it for.
>> By the way:
>> my experimental JavaZ library ( contains many
>> examples:
>> e.g. bindF (a.k.a. map) in Zyx has a version liftF in ZyxStatics (its
>> method reference is used in foreach)
>> Luc
>> --
>>   __~O
>>  -\ <,
>> (*)/ (*)
>> reality goes far beyond imagination

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