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From: =?UTF-8?Q?Arne_Vajh=c3=b8j?= <arne@vajhoej.dk>
Newsgroups: comp.lang.java.programmer
Subject: Re: How to handle methods in a common interface that supports different versions of a message format
Date: Mon, 9 Dec 2019 21:24:30 -0500
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On 12/9/2019 2:51 AM, mike wrote:
> Den lördag 7 december 2019 kl. 03:49:27 UTC+1 skrev Arne Vajhøj:
>> On 12/6/2019 2:55 AM, mike wrote:
>>> I would need some advice in the following issue:
>>> 
>>> public interface Netconf {
>>> 
>>> void methodA();
>>> 
>>> void methodB();
>>> 
>>> }
>>> 
>>> The issue I have is that methodA() only supports NETCONF message
>>> 1.0 and methodB() only supports NETCONF message 1.1
>>> 
>>> 1. Is it better to have separate interfaces like: Netconf and
>>> Netconf_1.1 ( better naming?) 2. If we use one interface,
>>> Netconf, and in the implementation we have a property for
>>> netconfVersion should I just throw exception if methodA() is
>>> called and we have set netconfVersion 1.1?
>>> 
>>> Any other considerations I need to do when supporting multiple
>>> versions of a message like NETCONF?
>> 
>> If you want to use proper typing then I like:
>> 
>> public interface Netconf { NetconfVersion getVersion(); }
>> 
>> public interface Netconf10 extends Netconf { void methodA(); }
>> 
>> public interface Netconf11 extends Netconf { void methodB(); }
>> 
>> Having methods that should not be there and that throws an
>> exception is not good IMHO.

> Thanks for the reply. I like the idea. I have a follow-up question:
> 
> Since we only had support for 1.0 user only used Netconf interface.
> Now we will return two types of interfaces Netconf10 or Netconf11.
> This would mean that users using 1.0 (Netconf) now need to use
> Netconf10 in those cases they need Netconf 1.0 specific
> methods.Correct?

If I understand you correctly then your concern is backwards
compatibility.

So if you today have:

public interface Netconf {
     void methodA();
}

public class NetconfFactory {
     public static Netconf getOne() {
         ...
     }
}

and client code:

Netconf nc = NetconfFactory.getOne();
nc.methodA();

Then you will need to either change client code to ref Netconf10 or
use different namings:

interface NetconfBase
interface Netconf extends NetconfBase
interface Netconf11 extends NetconfBase

Arne