minjcho commented on code in PR #22078:
URL: https://github.com/apache/kafka/pull/22078#discussion_r3278999866
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docs/streams/developer-guide/running-app.md:
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@@ -44,6 +44,118 @@ When you start your application you are launching a Kafka
Streams instance of yo
When the application instance starts running, the defined processor topology
will be initialized as one or more stream tasks. If the processor topology
defines any state stores, these are also constructed during the initialization
period. For more information, see the State restoration during workload
rebalance section).
+# Listeners and callbacks
+
+`KafkaStreams` provides several listeners and callbacks that let you observe
the internal state and behavior of your application. All listeners must be set
**before** calling `start()`. Attempting to set a listener after `start()` has
been called will throw an `IllegalStateException`. Each listener can only be
set once per `KafkaStreams` instance; setting a new listener replaces any
previously set listener.
Review Comment:
I have changed the wording, could you check if it is clear?
```diff
- Each listener can only be set once per `KafkaStreams` instance; setting
a new listener replaces any previously set listener.
+ A setter may be called multiple times before `start()`. Only the most
recent listener takes effect.
```
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