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As you can see this creates 1 StateStore, and in the Materialized parameter requires 1 initializer, and 1 aggValueSerde. The user no longer has to worry about the intermediate values and the joiners. All they have to think about is how each stream impacts the creation of the final CG object. The idea is that you can collect many grouped streams with overlapping key spaces and any kind of value types. Once aggregated its value will be reduced into one type. This is why the user need only one initializer. Each aggregator will need to integrate the new value with the new object made in the initializer.

When a new input arrives lets say at "topic1" it will first go through a KStreamAggreagte and grab the current aggregate from storeName1. It will add its incoming object to the aggregate, update the store and pass the new aggregate on. This new aggregate goes through the KStreamCogroup which is pretty much just a pass through processor and you are done. 

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