/*
 * 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.geode.cache.query;

/**
 * Behavior of a user-defined aggregator. Aggregates values and returns a result. In addition to the
 * methods in the interface, implementing classes must have a 0-arg public constructor.
 */
public interface Aggregator {

  /**
   * Initialize the Aggregator
   */
  void init();

  /**
   * Accumulate the next scalar value
   *
   * @param value the scalar value to accumulate
   */
  void accumulate(Object value);

  /**
   * Finish the aggregation and return the operation result.
   *
   * @return Return the result scalar value
   */
  Object terminate();
}
