org.apache.kafka.streams.kstream.Initializer Maven / Gradle / Ivy
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* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
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* See the License for the specific language governing permissions and
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*/
package org.apache.kafka.streams.kstream;
/**
* The {@code Initializer} interface for creating an initial value in aggregations.
* {@code Initializer} is used in combination with {@link Aggregator}.
*
* @param aggregate value type
* @see Aggregator
* @see KGroupedStream#aggregate(Initializer, Aggregator)
* @see KGroupedStream#aggregate(Initializer, Aggregator, Materialized)
* @see TimeWindowedKStream#aggregate(Initializer, Aggregator)
* @see TimeWindowedKStream#aggregate(Initializer, Aggregator, Materialized)
* @see SessionWindowedKStream#aggregate(Initializer, Aggregator, Merger)
* @see SessionWindowedKStream#aggregate(Initializer, Aggregator, Merger, Materialized)
*/
public interface Initializer {
/**
* Return the initial value for an aggregation.
*
* @return the initial value for an aggregation
*/
VA apply();
}