8182482: Module System spec updates

[Alex Buckley]

Hi Remi,

On 6/20/2017 6:29 AM, forax at univ-mlv.fr wrote:
> ok, let's focus on abstract class defining a service.

I would be happy for the "Designing services" section to give more 
advice about the tradeoffs between an interface and an abstract class. 
Two sentences, written in a style that leads a junior developer but does 
not judge them if they don't follow the advice. Can you write it? :-

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A service is a single type, usually an interface or abstract class. 
***REMI'S TEXT HERE*** A concrete class can be used, but this is not 
recommended. The type may have any accessibility.

The methods of a service are highly ...
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Alex