[rfc][icedtea-web] immutbale transaltor

[Jiri Vanek]

On 09/17/2014 09:57 PM, Omair Majid wrote:
> * Jiri Vanek <jvanek at redhat.com> [2014-09-17 07:00]:


ok. I thought the answer will be like that:)

Note - I do not insist on this patch. But I would really like to know why is which approach better.
They both have advantages and disadvantages.  From my point of view, the "my" approach is little bit 
better.

>> Attached patch is changing our new Transaltor to be immutable.
>
> That's great! I love immutable classes!
>
>> And so get rid of enum in favor of class, and so use handler idiom for creation....
>
> Wait, what. How does this follow from the above?

Testability?

>
>> Personally,  why people use enums for singletons?!?!?!
>
> Please see Effective Java for an explanation. There's a summary on
> StackOverflow [0] too.

I read both. The approaches seems to me equal.  And whether use enum or "my" depends on actual needs.

>
>> Well very simple
>> singletons .. yes, but once there is some logic... Ouch they are so so
>> *clumsy* ... So clamsy taht they can not be even properly tested ( no
>> instance!, no overrload!).
>
>> And once singleton is not immutbale.... Is it still singleton?
>
> A singleton is a class designed to be instantiated (at max) once. It
> should not be instantiated again. If you class is, by design, acceptable
> to instantiate more than once, then it's not a singleton.

Is lit like that? :)) Yes, the "A singleton is a class designed to be instantiated (at max) once. " 
is absolutely correct. But in scope of application, not universe,or not?

 From definition of singleton is clear that it have to have max 1 isntance in app. But nowhere is 
written, that you are forbid to create testing instances.
>
> I am not sure how immutability affects singleton. I mean, most
> singletons are mutable, but it might be possible that you have a global
> shared resources that can be initialized only once and is basically
> immutable (or a constant) after.
>
>> +    Translator() {
>
>> +    Translator(String s) {
>
>> +    Translator(ResourceBundle resources) {
>
> Is it intentional that these constructs are now visible package-wide?
> Because this kind of violates the singleton instance requirement. I

Does it? The principle says, that there is none or one isntance, not that you are not allwoed to 
create another (esepcially for testing)

> mean, it's fine if you want to lean more heavily towards having a
> testable class rather than
> hell-will-break-loose-if-another-instance-of-this-class-is-created

It does not :)
> class.
>
> Thanks,
> Omair
>
> [0] http://stackoverflow.com/a/71399/3561275

Thank you!

However, the benefits of enum over the holder pattern (in this case) were not told:)

Any ideas how to
  - keep enum, made it immutbale, and test it?
or
  - made it immutbale, testable and eget rid of those constructors?
    - here I have idea - to made the properties actually protected final. And to hide all 
contructors in Transaltor itself, but create special constructor in TestableTrasnslator?



Again, thank you for inputs.


J