content: /*
   * 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,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  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 <VAgg> 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)
   */
  @FunctionalInterface
  public interface Initializer<VAgg> {
  
      /**
       * Return the initial value for an aggregation.
       *
       * @return the initial value for an aggregation
       */
      VAgg apply();
  }
  