In looking at https://ci.apache.org/projects/flink/flink-docs-release-1.4/dev/stream/operators/windows.html#processwindowfunction-with-incremental-aggregation, I noticed a few errors...
- "This allows to incrementally compute windows" should be "This allows it to incrementally compute windows"
- DataStream<Tuple2<String, Long> input = ...; should be DataStream<Tuple2<String, Long>> input = ...;
- The getResult() method needs to cast one of the accumulator values to a double, if that's what it is going to return.
- MyProcessWindowFunction needs to extend, not implement ProcessWindowFunction
- MyProcessWindowFunction needs to implement a process() method, not an apply() method.
- The call to .timeWindow takes a Time parameter, not a window assigner.