[jira] [Created] (KAFKA-7435) Consider standardizing the config object pattern on interface/implementation.

["John Roesler (JIRA)" <ji...@apache.org>]

John Roesler created KAFKA-7435:
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             Summary: Consider standardizing the config object pattern on interface/implementation.
                 Key: KAFKA-7435
                 URL: https://issues.apache.org/jira/browse/KAFKA-7435
             Project: Kafka
          Issue Type: Improvement
          Components: streams
            Reporter: John Roesler
             Fix For: 3.0.0


Currently, the majority of Streams's config objects are structured as a "external" builder class (with protected state) and an "internal" subclass exposing getters to the state. This is serviceable, but there is an alternative we can consider: to use an interface for the external API and the implementation class for the internal one.

Advantages:
 * we could use private state, which improves maintainability
 * the setters and getters would all be defined in the same class, improving readability
 * users browsing the public API would be able to look at an interface that contains less extraneous internal details than the current class
 * there is more flexibility in implementation

Alternatives
 * instead of external-class/internal-subclass, we could use an external *final* class with package-protected state and an internal accessor class (not a subclass, obviously). This would make it impossible for users to try and create custom subclasses of our config objects, which is generally not allowed already, but is currently a runtime class cast exception.

Example implementation: [https://github.com/apache/kafka/pull/5677]

This change would break binary, but not source, compatibility, so the earliest we could consider it is 3.0.

To be clear, I'm *not* saying this *should* be done, just calling for a discussion. Otherwise, I'd make a KIP.

Thoughts?



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