Hi Andy, This is a big change, and I don't think there has been a lot of discussion about the pros and cons. What specific benefits do we get from transitioning to using an interface rather than an abstract class?
If we are serious about doing this, would it be cleaner to just change AdminClient from an abstract class to an interface in Kafka 3.0? It would break binary compatibility, but you have to break binary compatibility in any case to get what you want here (no abstract class). And it would have the advantage of not creating a lot of churn in the codebase as people replaced "AdminClient" with "Admin" all over the place. What do you think? On a related note, one problem I've seen is that people will subclass AdminClient for testing. Then, every time Kafka adds a new API, we add a new abstract method to the base class, which breaks compilation for them. Their test classes would have been fine simply failing when the new API was called. So perhaps one useful class would be a class that implements the AdminClient API, and throws UnimplementedException for every method. The test classes could subclass this method and never have to worry about new methods getting added again. Another pattern I've seen is people wanting to implement a class which is similar to KafkaAdminClient in every way, except for the behavior of close(). Specifically, people want to implement reference counting in order to reuse AdminClient instances. So they start by implementing essentially a delegating class, which just forwards every method to an underlying AdminClient instance. But this has the same problem that it breaks every time the upstream project adds an API. In order to support this, we could have an official DelegatingAdminClient base class that forwarded every method to an underlying AdminClient instance. Then the client code could override the methods they needed, like close. best, Colin On Tue, Jun 4, 2019, at 09:17, Andy Coates wrote: > Hi folks > > As there's been no chatter on this KIP I'm assuming it's non-contentious, > (or just boring), hence I'd like to call a vote for KIP-476: > > https://cwiki.apache.org/confluence/display/KAFKA/KIP-476%3A+Add+Java+AdminClient+Interface > > Thanks, > > Andy >
