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Because the added interface methods are default with a reasonable default, those additions are backwards compatible. However, given that now there would be two ways
A user may continue to "connect" state stores to a low level processor, we would have to specify how they behave together. I believe the correct decision is to enforce that for a given call of processor by passing stateStoreNames when calling stream.process/transform(...) or stream.transform(...) it should only be possible to specify state stores one of the two ways, either through the stateStoreNames argument or by implementing the stores method of ConnectedStoreProvider . Specifically: if ConnectedStoreProvider::stores returns non-null and stateStoreNames is passed, an exception will be thrown making it clear that the user should choose one way or the other. This may be used in combination with a Supplier that provides its own state stores by implementing ConnectedStoreProvider::stores() .
If a StoreBuilder that was manually added is also returned by a ConnectedStoreProvider , there is no issue since adding a state store will now be idempotent.
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