Package org.apache.kafka.streams.kstream

Interface Reducer<V>

Type Parameters:

V - value type

public interface Reducer<V>

The Reducer interface for combining two values of the same type into a new value. In contrast to Aggregator the result type must be the same as the input type.

The provided values can be either original values from input KeyValue pair records or be a previously computed result from apply(Object, Object).

Reducer can be used to implement aggregation functions like sum, min, or max.

See Also:

• KGroupedStream.reduce(Reducer)
• KGroupedStream.reduce(Reducer, Materialized)
• TimeWindowedKStream.reduce(Reducer)
• TimeWindowedKStream.reduce(Reducer, Materialized)
• SessionWindowedKStream.reduce(Reducer)
• SessionWindowedKStream.reduce(Reducer, Materialized)
• Aggregator

Method Summary

Modifier and Type	Method	Description
V	apply(V value1, V value2)	Aggregate the two given values into a single one.

Method Details

apply

V apply(V value1,
 V value2)

Aggregate the two given values into a single one.

Parameters:

value1 - the first value for the aggregation

value2 - the second value for the aggregation

Returns:

the aggregated value