| Interface | Description | 
|---|---|
| AsyncFlatMapFunction<M,OM> | Asynchronous variant of the  FlatMapFunctionused in tandem withMessageStream.flatMapAsync(AsyncFlatMapFunction)to transform a collection of 0 or more messages. | 
| ClosableFunction | A function that can be closed after its execution. | 
| FilterFunction<M> | Specifies whether a message should be retained for further processing. | 
| FlatMapFunction<M,OM> | Transforms an input message into a collection of 0 or more messages, possibly of a different type. | 
| FoldLeftFunction<M,WV> | Incrementally updates the aggregated value as messages are added. | 
| InitableFunction | A function that can be initialized before execution. | 
| JoinFunction<K,M,JM,RM> | Joins incoming messages in two streams by key. | 
| MapFunction<M,OM> | Transforms an input message into another message, possibly of a different type. | 
| ScheduledFunction<K,OM> | Allows scheduling a callback for a specific epoch-time. | 
| SinkFunction<M> | Allows sending a message to an output system. | 
| StreamTableJoinFunction<K,M,R,JM> | Joins incoming messages with records from a table by the join key. | 
| SupplierFunction<T> | A supplier to return a new value at each invocation | 
| WatermarkFunction<T> | Allows handling of watermarks. |