Which of the following is NOT a stateless operator in Kafka Streams?

• A. foreach
• B. map
• C. join
• D. branch

Answer: (C)

Kafka Streams differentiates stateless and stateful operators. Stateless operators process each record independently and don’t rely on previously seen data. Map applies a function to each record and emits a transformed one; foreach performs side effects per record without storing state; branch routes each input to different outputs based on a predicate and doesn’t need to remember past events. Join, however, is stateful because producing joined results requires keeping past records from one or both streams (often within a window) in a state store to be matched together. So the operator that is not stateless is join.