Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.java.programmer > #24762

Re: Interface with implied Constructor

Show all headers | View raw

On 07/19/2013 04:38 PM, Gene Wirchenko wrote:
> On Thu, 18 Jul 2013 23:21:35 -0300, Arved Sandstrom
> <asandstrom2@eastlink.ca> wrote:
>
> [snip]
>
>> I'll be honest, Robert, personally I consider the behaviour of an object
>> - the kinds of things you could specify in an interface - to be what the
>> *initialized* object can (should) do.
>
>       But there is more to it than that.  There is also getting it
> initialised.  That should also be part of the API.  I would not
> enforce that it has to, but I sure would like the option to specify
> constructor signatures in an interface.

Apart from other problems with constructors in interfaces (e.g. a class 
implements 2 interfaces, both of which have constructors: which ctor do 
you ignore and hence violate a contract?), what do you intend to mandate 
by requiring a constructor with a given signature? That all implementing 
classes create matching private fields that are exposed by accessors? 
Why would you want to do that?

Although it's usually an anti-pattern, I believe a better idea would be 
to specify some important getters in an interface, if you need something 
like this. Rather than wanting to control how an object initializes 
itself and is implemented, typically what you're really after is to 
require that an object can provide some synthetic state information.

>> I seriously dislike init() methods, not just in Java. Particularly if
>> there is no sensible un-init()'ed object for the class. I just don't see
>> any credible argument for them. Like Richard said, actually: "half-baked".
>>
>> Often the best way to properly initialize an object is to call a
>> constructor with arguments. That's what they are for. And to be honest
>> once again, a ctor *is* an implementation thing, IMO: it's not the
>
>       A method is an implementation thing, too, but we have interface
> specifications for them.

The *body* of a method is implementation. Interface or no interface, the 
method as called, the way it represents to callers, is behaviour.

I've seen people in threads make your argument. To call everything 
behaviour is not helpful. A constructor builds an object. I don't 
consider that behaviour.

>> business of an interface to dictate how an implementation will
>> initialize objects that can support the interface contract. After all,
>
>        That is exactly what it is for.  How the implementation works is
> not the business of the interface, but how to call it is.

I don't consider a constructor a "call". Invoking a method on a properly 
initialized method, yes; *building* the object, no.

>> how can an interface even possibly imagine what the internal state of an
>> initialized object, hence what ctor args are required, is?
>
>       Internal state is implementation and so is not in an interface's
> scope.  How to call it is.
>
>> No problem with factory methods, except they are for specific
>> situations. And I think they also lean more towards implementation.
>
> Sincerely,
>
> Gene Wirchenko
>
AHS

-- 
When a true genius appears, you can know him by this sign:
that all the dunces are in a confederacy against him.
-- Jonathan Swift

Back to comp.lang.java.programmer | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Interface with implied Constructor Richard Maher <maher_rjSPAMLESS@hotmail.com> - 2013-07-09 18:41 +0800
  Re: Interface with implied Constructor Robert Klemme <shortcutter@googlemail.com> - 2013-07-09 04:08 -0700
    Re: Interface with implied Constructor Richard Maher <maher_rjSPAMLESS@hotmail.com> - 2013-07-10 06:46 +0800
      Re: Interface with implied Constructor Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-07-09 21:08 -0400
      Re: Interface with implied Constructor Kevin McMurtrie <mcmurtrie@pixelmemory.us> - 2013-07-11 19:11 -0700
        Re: Interface with implied Constructor Robert Klemme <shortcutter@googlemail.com> - 2013-07-14 17:53 +0200
          Re: Interface with implied Constructor Kevin McMurtrie <mcmurtrie@pixelmemory.us> - 2013-07-15 08:58 -0700
            Re: Interface with implied Constructor Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2013-07-15 10:57 -0700
              [OT] Re: Interface with implied Constructor Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-07-15 14:13 -0400
                Re: [OT] Re: Interface with implied Constructor Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2013-07-15 12:58 -0700
            Re: Interface with implied Constructor Robert Klemme <shortcutter@googlemail.com> - 2013-07-15 20:45 +0200
      Re: Interface with implied Constructor Robert Klemme <shortcutter@googlemail.com> - 2013-07-14 18:03 +0200
        Re: Interface with implied Constructor Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-07-18 23:21 -0300
          Re: Interface with implied Constructor Gene Wirchenko <genew@telus.net> - 2013-07-19 12:38 -0700
            Re: Interface with implied Constructor Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-07-19 17:56 -0300
              Re: Interface with implied Constructor Gene Wirchenko <genew@telus.net> - 2013-07-22 12:39 -0700
                Re: Interface with implied Constructor Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-07-22 16:02 -0400
                Re: Interface with implied Constructor Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-07-22 18:08 -0300
                Re: Interface with implied Constructor Gene Wirchenko <genew@telus.net> - 2013-07-23 14:32 -0700
                Re: Interface with implied Constructor Jim Gibson <jimsgibson@gmail.com> - 2013-07-23 14:43 -0700
                Re: Interface with implied Constructor Gene Wirchenko <genew@telus.net> - 2013-07-24 13:27 -0700
                Re: Interface with implied Constructor Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-07-24 18:20 -0300
                Re: Interface with implied Constructor Robert Klemme <shortcutter@googlemail.com> - 2013-07-26 00:03 +0200
                Re: Interface with implied Constructor Martin Gregorie <martin@address-in-sig.invalid> - 2013-07-24 21:18 +0000
                Re: Interface with implied Constructor Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-07-24 17:42 -0400
                Re: Interface with implied Constructor Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-07-23 18:19 -0400
                Re: Interface with implied Constructor Gene Wirchenko <genew@telus.net> - 2013-07-24 13:31 -0700
                Re: Interface with implied Constructor Steven Simpson <ss@domain.invalid> - 2013-07-27 04:06 +0100
            Re: Interface with implied Constructor Martin Gregorie <martin@address-in-sig.invalid> - 2013-07-19 21:21 +0000
              Re: Interface with implied Constructor Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-07-19 18:56 -0300
                Re: Interface with implied Constructor Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-07-19 18:10 -0400
                Re: Interface with implied Constructor Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-07-19 20:46 -0300
                Re: Interface with implied Constructor Richard Maher <maher_rjSPAMLESS@hotmail.com> - 2013-07-20 12:42 +0800
                Re: Interface with implied Constructor Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-07-20 09:08 -0300
                Re: Interface with implied Constructor Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-07-20 09:08 -0400
              Re: Interface with implied Constructor Kevin McMurtrie <mcmurtrie@pixelmemory.us> - 2013-07-19 19:20 -0700
                Re: Interface with implied Constructor markspace <markspace@nospam.nospam> - 2013-07-19 20:11 -0700
                Re: Interface with implied Constructor Richard Maher <maher_rjSPAMLESS@hotmail.com> - 2013-07-20 12:26 +0800
                Re: Interface with implied Constructor Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-07-20 09:38 -0300
              Re: Interface with implied Constructor Robert Klemme <shortcutter@googlemail.com> - 2013-07-20 19:46 +0200
                Re: Interface with implied Constructor Martin Gregorie <martin@address-in-sig.invalid> - 2013-07-20 19:12 +0000
                Re: Interface with implied Constructor Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-07-20 17:12 -0400
                Re: Interface with implied Constructor Martin Gregorie <martin@address-in-sig.invalid> - 2013-07-20 21:18 +0000
                Re: Interface with implied Constructor Robert Klemme <shortcutter@googlemail.com> - 2013-07-21 12:13 +0200
                Re: Interface with implied Constructor Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-07-21 16:18 -0300
                Re: Interface with implied Constructor markspace <markspace@nospam.nospam> - 2013-07-21 13:45 -0700
                Re: Interface with implied Constructor Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-07-21 16:58 -0400
                Re: Interface with implied Constructor Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-07-21 21:19 -0300
          Re: Interface with implied Constructor Robert Klemme <shortcutter@googlemail.com> - 2013-07-20 20:09 +0200
            Re: Interface with implied Constructor Robert Klemme <shortcutter@googlemail.com> - 2013-07-20 20:21 +0200
            Re: Interface with implied Constructor Joerg Meier <joergmmeier@arcor.de> - 2013-07-20 23:17 +0200
              Re: Interface with implied Constructor Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-07-20 17:32 -0400
                Re: Interface with implied Constructor Joerg Meier <joergmmeier@arcor.de> - 2013-07-21 00:10 +0200
            Re: Interface with implied Constructor Arved Sandstrom <asandstrom2@eastlink.ca> - 2013-07-21 17:53 -0300
  Re: Interface with implied Constructor markspace <markspace@nospam.nospam> - 2013-07-09 18:13 -0700
    Re: Interface with implied Constructor Richard Maher <maher_rjSPAMLESS@hotmail.com> - 2013-07-10 18:03 +0800
      Re: Interface with implied Constructor markspace <markspace@nospam.nospam> - 2013-07-10 08:41 -0700
        Re: Interface with implied Constructor Richard Maher <maher_rjSPAMLESS@hotmail.com> - 2013-07-11 06:53 +0800
  Re: Interface with implied Constructor Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2013-07-09 21:41 -0700
    Re: Interface with implied Constructor Richard Maher <maher_rjSPAMLESS@hotmail.com> - 2013-07-10 17:55 +0800
    Re: Interface with implied Constructor Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2013-07-10 14:52 -0700
  Re: Interface with implied Constructor Roedy Green <see_website@mindprod.com.invalid> - 2013-07-10 16:02 -0700

csiph-web